Adenomatous Polyposis Coli Truncation Alters Cytoskeletal Structure and Microtubule Stability in Early Intestinal Tumorigenesis

Journal of Gastrointestinal Surgery : Official Journal of the Society for Surgery of the Alimentary Tract. Nov-Dec, 2002  |  Pubmed ID: 12504226

Partial loss of function of adenomatous polyposis coli (APC) protein by truncation of its carboxy (C)-terminus is an early factor in the development of many sporadic colorectal cancers. In the C57BL/6J Min/+ (Min/+) mouse, an animal with a germline mutation of Apc, we found that APC truncation was associated with reduced enterocyte migration and loss of association and membrane expression of adherens junction proteins. We hypothesized that these defects were related to changes in cytoskeletal function resulting from truncation of the APC C-terminus, which contains microtubule binding regions, as well as putative sites for indirect actin binding. We investigated this further by determining whether APC truncation produced in vivo changes in actin cytoskeletal structure and microtubule stability. The actin cytoskeleton of histologically normal enterocytes from Min/+ mice was compared to that of Apc+/+ (wild-type) mice by confocal indirect immunofluorescence microscopy. We found a significant loss of actin localization at the apical plasma membrane in Min/+ enterocytes. In addition, immunoblotting revealed increased levels of both unstable Tyr-tubulin and alpha-tubulin turnover in Min/+ enterocytes, indicating an alteration in microtubule dynamics. These studies suggest that loss of actin localization and changes in microtubule dynamics may be dominant negative effects of truncated APC. These changes are consistent with the defects in enterocyte migration and junctional complex formation observed in the Min/+ model of early APC-associated colorectal tumorigenesis.

Energy Metabolism During Larval Development of Green and White Abalone, Haliotis Fulgens and H. Sorenseni

The Biological Bulletin. Jun, 2003  |  Pubmed ID: 12807704

An understanding of the biochemical and physiological energetics of lecithotrophic development is useful for interpreting patterns of larval development, dispersal potential, and life-history evolution. This study investigated the metabolic rates and use of biochemical reserves in two species of abalone, Haliotis fulgens (the green abalone) and H. sorenseni (the white abalone). Larvae of H. fulgens utilized triacylglycerol as a primary source of endogenous energy reserves for development ( approximately 50% depletion from egg to metamorphic competence). Amounts of phospholipid remained constant, and protein dropped by about 30%. After embryogenesis, larvae of H. fulgens had oxygen consumption rates of 81.7 +/- 5.9 (SE) pmol larva(-1) h(-1) at 15 degrees C through subsequent development. The loss of biochemical reserves fully met the needs of metabolism, as measured by oxygen consumption. Larvae of H. sorenseni were examined during later larval development and were metabolically and biochemically similar to H. fulgens larvae at a comparable stage. Metabolic rates of both species were very similar to previous data for a congener, H. rufescens, suggesting that larval metabolism and energy utilization may be conserved among closely related species that also share similar developmental morphology and feeding modes.

Fisheries: Mislabelling of a Depleted Reef Fish

Nature. Jul, 2004  |  Pubmed ID: 15254528

Any fish species that appears to be readily available in the marketplace will create an impression among the public that there is a plentiful supply of that fish in the sea, but this may belie the true state of the fisheries' stock. Here we use molecular genetic analysis to show that some three-quarters of the fish sold in the United States as 'red snapper'--the US Food and Drug Administration's legally designated common name for Lutjanus campechanus--belong to another species. Mislabelling to this extent not only defrauds consumers but could also adversely affect estimates of stock size if it influences the reporting of catch data that are used in fisheries management.

Apc Deficiency is Associated with Increased Egfr Activity in the Intestinal Enterocytes and Adenomas of C57BL/6J-Min/+ Mice

The Journal of Biological Chemistry. Oct, 2004  |  Pubmed ID: 15294912

Overexpression of the epidermal growth factor receptor (EGFR) and its increased tyrosine kinase activity are implicated in colorectal cancer (CRC) development and malignant progression. The C57BL/6J-Min/+ (Min/+) mouse is a model for CRC and develops numerous intestinal adenomas. We analyzed the normal mucosa of Min/+ and Apc+/+ (WT) littermate mice together with Apc-null adenomas to gain insight into the roles of Egfr in these intestinal tissues. Protein analyses showed that Egfr activity was highest in the tumors, and also up-regulated in Min/+ relative to WT enterocytes. Expression of ubiquitylated Egfr (Egfr-Ub) was increased in Min/+ enterocytes and tumors. Tumors exhibited increased association of Egfr with clathrin heavy chain (CHC), Gab1, and p85alpha, the regulatory subunit of phosphoinositide 3-kinase (PI3K), and tumors also overexpressed c-Src, PDK1, and Akt. Immunohistochemistry for Akt-p-Ser473 revealed a low level of this active kinase in Min/+ and WT enterocytes and its strong presence in tumors. Prostaglandin E2 (PGE2) is a product of cyclooxygenase-2 (Cox-2) activity that is up-regulated in Min/+ tumors and transactivates Egfr. PGE2 expression was significantly higher in untreated Min/+ tumors and reduced by treatment with the Cox-2 inhibitor, celecoxib. Dietary administration of this NSAID also inhibited Egfr activity in tumors. Increased activation of the EGFR-PI3K-Akt signaling pathway in tumors relative to Apc+/+ and ApcMin/+ enterocytes provides potential opportunities for therapeutic interventions to differentially suppress tumor formation, promotion, progression, and/or recurrence.

Egg Size Evolution in Tropical American Arcid Bivalves: the Comparative Method and the Fossil Record

Evolution; International Journal of Organic Evolution. Dec, 2004  |  Pubmed ID: 15696750

Marine organisms exhibit a wide range of egg sizes, even among closely related taxa, and egg size is widely considered to be one of the most important components of the life histories of marine species. The nature of the trade-off between egg size and number and the consequences of variation in egg size for offspring growth and survivorship have been extensively modeled. Yet, there is little empirical evidence that supports the relative importance of particular environmental parameters in engendering the tremendous variation in egg size seen in marine organisms. This study compares egg sizes between six geminate species pairs of bivalves in the family Arcidae to determine whether egg size differs in predictable directions between geminate species in the two oceans separated by the Central American isthmus, and whether the direction and timing of egg size evolution among geminates in this family is correlated with both modern and paleoceanographic patterns of oceanic productivity. In all modern members of six geminate pairs, egg size was larger in the species in the western Atlantic than in its sister species the eastern Pacific. This pattern supports the hypothesis that optimal egg size differs in the two oceans due to the low productivity and poor larval feeding environment in the western Atlantic relative to the eastern Pacific. The fossil record of one geminate pair shows that egg size has remained consistently large in the western Atlantic from the Miocene to the Recent, while egg size in the eastern Pacific has decreased to the current small size in less than 2 million years; this suggests that modern-day differences between egg sizes in the western Atlantic and eastern Pacific are due to either an increase in productivity in the eastern Pacific and subsequent selection for smaller eggs in that ocean, or differential patterns of extinction that occurred well after the rise of the isthmus. These results agree with ancestral character state reconstruction using linear parsimony, but differ from squared-change parsimony reconstructions.

Carnosol Inhibits Beta-catenin Tyrosine Phosphorylation and Prevents Adenoma Formation in the C57BL/6J/Min/+ (Min/+) Mouse

Cancer Research. Feb, 2005  |  Pubmed ID: 15705912

Carnosol, a constituent of the herb, rosemary, has shown beneficial medicinal and antitumor effects. Using the C57BL/6J/Min/+ (Min/+) mouse, a model of colonic tumorigenesis, we found that dietary administration of 0.1% carnosol decreased intestinal tumor multiplicity by 46%. Previous studies showed that tumor formation in the Min/+ mouse was associated with alterations in the adherens junctions, including an increased expression of tyrosine-phosphorylated beta-catenin, dissociation of beta-catenin from E-cadherin, and strongly reduced amounts of E-cadherin located at lateral plasma membranes of histologically normal enterocytes. Here, we confirm these findings and show that treatment of Min/+ intestinal tissue with carnosol restored both E-cadherin and beta-catenin to these enterocyte membranes, yielding a phenotype similar to that of the Apc(+/+) wild-type (WT) littermate. Moreover, treatment of WT intestine with the phosphatase inhibitor, pervanadate, removed E-cadherin and beta-catenin from the lateral membranes of enterocytes, mimicking the appearance of the Min/+ tissue. Pretreatment of WT tissue with carnosol inhibited the pervanadate-inducible expression of tyrosine-phosphorylated beta-catenin. Thus, the Apc(Min) allele produces adhesion defects that involve up-regulated expression of tyrosine-phosphorylated proteins, including beta-catenin. Moreover, these data suggest that carnosol prevents Apc-associated intestinal tumorigenesis, potentially via its ability to enhance E-cadherin-mediated adhesion and suppress beta-catenin tyrosine phosphorylation.

Soleus and EDL Muscle Contractility Across the Lifespan of Female C57BL/6 Mice

Experimental Gerontology. Dec, 2005  |  Pubmed ID: 16243468

All previous aging research on the contractility of rodent skeletal muscle has been conducted on male rodents. Because males and females age differently, we undertook this study to determine if and when age-related decrements in skeletal muscle contractility occur in female mice. Soleus and extensor digitorum longus (EDL) muscles from female C57BL/6 mice aged approximately 4, 8, 16, 24 and 28 mo were assessed in vitro for contractility and subsequently contractile protein content. EDL muscle was resistant to age-related changes in force generation but displayed characteristics of becoming more slow-twitch like. Maximal isometric tetanic force (Po) generated by soleus muscle declined with age. Soleus muscle size and contractile protein contents were not affected by age and thus could not explain the age-related force decrements. Soleus muscle specific Po declined with age being approximately 26% lower in muscles of 16-28 mo-old mice indicating that a deterioration in soleus muscle quality of female mice occurred beginning around the age of ovarian failure. Thus this study provides essential, comprehensive baseline data for future studies on age-related muscle dysfunction in the female mouse.

Modulation of Tumor Formation and Intestinal Cell Migration by Estrogens in the Apc(Min/+) Mouse Model of Colorectal Cancer

Carcinogenesis. Mar, 2005  |  Pubmed ID: 15579483

Epidemiological studies suggest that post-menopausal hormone replacement therapy (HRT) reduces colorectal cancer (CRC) incidence. Phytoestrogens, including the soy isoflavone genistein and coumestrol, are used by many women as alternatives to HRT. Previous studies showed that ovariectomy induced a 77% increase in intestinal adenoma number in the C57BL/6J-Min/+ (Min/+) mouse, an animal model of adenomatous polyposis coli (APC)-associated CRC. Replacement of estradiol (E(2)) in ovariectomized Min/+ mice reduced tumor number to baseline and up-regulated the expression of estrogen receptor beta (ERbeta). We hypothesized that the phytoestrogens genistein and coumestrol would inhibit intestinal tumorigenesis in ovariectomized Min/+ mice. Min/+ and Apc(+/+) (WT) mice were ovariectomized and assigned to either a control diet or treatment with E(2), genistein or coumestrol. Treatment of ovariectomized Min/+ (Min/+ OX) mice with genistein resulted in a non-significant reduction in tumor number. Min/+ OX mice treated with coumestrol had significantly fewer tumors than untreated Min/+ OX controls and the same number of tumors as non-ovariectomized Min/+ mice. Bromodeoxyuridine migration assays also demonstrated that treatment with E(2) or coumestrol improved enterocyte migration rate. Immunoprecipitation and immunohistochemistry analyses showed that impaired association of the adherens junction proteins E-cadherin and beta-catenin in Min/+ mice was improved by treatment with either E(2) or coumestrol. Immunoblot analyses also showed that expression of ERbeta was elevated in enterocytes of Min/+ OX mice treated with E(2) or coumestrol as compared with those of untreated Min/+ OX mice. In conclusion, both coumestrol and E(2) prevent intestinal tumorigenesis and ameliorate enterocyte migration and intercellular adhesion in the Apc(Min/+) mouse model of CRC.

Removal of Ovarian Hormones from Mature Mice Detrimentally Affects Muscle Contractile Function and Myosin Structural Distribution

Journal of Applied Physiology (Bethesda, Md. : 1985). Feb, 2006  |  Pubmed ID: 16254070

The purposes of this study were to determine the effects of ovarian hormone removal on force-generating capacities and contractile proteins in soleus and extensor digitorum longus (EDL) muscles of mature female mice. Six-month-old female C57BL/6 mice were randomly assigned to either an ovariectomized (OVX; n = 13) or a sham-operated (sham; n = 13) group. In vitro contractile function of soleus and EDL muscles were determined 60 days postsurgery. Total protein and contractile protein contents were quantified, and electron paramagnetic resonance (EPR) spectroscopy was used to determine myosin structural distribution during contraction. OVX mice weighed 15% more than sham mice 60 days postsurgery, and soleus and EDL muscle masses were 19 and 15% greater in OVX mice, respectively (P < or = 0.032). Soleus and EDL muscles from OVX mice generated less maximal isometric force than did those from sham mice [soleus: 0.27 (SD 0.04) vs. 0.22 N.cm.mg(-1) (SD 0.04); EDL: 0.33 (SD 0.04) vs. 0.27 N.cm.mg(-1) (SD 0.04); P < or = 0.006]. Total and contractile protein contents of soleus and EDL muscles were not different between OVX and sham mice (P > or = 0.242), indicating that the quantity of contractile machinery was not affected by removing ovarian hormones. EPR spectroscopy showed that the fraction of strong-binding myosin during contraction was 15% lower in EDL muscles from OVX mice compared with shams [0.277 (SD 0.039) vs. 0.325 (SD 0.020); P = 0.004]. These results indicate that the loss of ovarian hormones has detrimental effects on skeletal muscle force-generating capacities that can be explained by altered actin-myosin interactions.

Deficient E-cadherin Adhesion in C57BL/6J-Min/+ Mice is Associated with Increased Tyrosine Kinase Activity and RhoA-dependent Actomyosin Contractility

Experimental Cell Research. Feb, 2006  |  Pubmed ID: 16368433

The Min/+ mouse is a model for APC-dependent colorectal cancer (CRC). We showed that tumorigenesis in this animal was associated with decreased E-cadherin adhesion and increased epidermal growth factor receptor (Egfr) activity in the non-tumor intestinal mucosa. Here, we tested whether these abnormalities correlated with changes in the actin cytoskeleton due to increased Rho-ROCK signaling. We treated Apc+/+ (WT) littermate small intestine with EGTA, an inhibitor of E-cadherin, and with LPA, an RhoA activator; both induced effects on adhesion and kinase activity that mimicked the Min/+ phenotype. GTP-bound Rho was increased in Min/+ enterocytes relative to WT. Since RhoA activity is associated with actomyosin contractility, markers of this signaling cascade were assessed including phosphorylated myosin light chain (MLC), cofilin, Pyk2, Src, and MAPK kinases. The increased actomyosin contractility characterizing Min/+ intestinal tissue was suppressed by the ROCK inhibitor, Y27632, but was inducible in the WT by EGTA or LPA. Finally, ultrastructural imaging revealed changes consistent with actomyosin contractility in Min/+ enterocytes. Thus, the positive regulation of E-cadherin adhesion provided by Apc+ in vivo allows proper negative regulation of Egfr, Src, Pyk2, and MAPK, as well as RhoA activities.

Changes in Antitumor Response in C57BL/6J-Min/+ Mice During Long-term Administration of a Selective Cyclooxygenase-2 Inhibitor

Cancer Research. Jun, 2006  |  Pubmed ID: 16778222

Selective cyclooxygenase-2 (COX-2) inhibitors are widely prescribed for severe arthritis and are currently under study in human chemoprevention trials. Recently, long-term use of these agents has come under scrutiny due to reports of treatment-associated cardiovascular toxicity. On short-term administration, the selective COX-2 inhibitor celecoxib inhibits adenoma growth in animal tumor models, including the C57BL/6J-Min/+ (Min/+) mouse. With uninterrupted long-term celecoxib administration, intestinal tumors in Min/+ mice initially regressed and then recurred to levels comparable with untreated controls. Celecoxib treatment initially suppressed COX-2 and prostaglandin E2 (PGE2) expression, but long-term use produced significantly higher levels of these molecules and reactivated PGE2-associated growth factor signaling pathways in tumor and normal tissues. These results indicate that COX-2 is an important chemoprevention target and that inhibition of this enzyme alters a paracrine enterocyte regulatory pathway. Chronic uninterrupted celecoxib treatment, however, induces untoward effects that enhance early progression events in intestinal tumorigenesis and may contribute to treatment toxicity.

Integrating Function Across Marine Life Cycles

Integrative and Comparative Biology. Oct, 2006  |  Pubmed ID: 21672768

Complex life cycles involve a set of discrete stages that can differ dramatically in form and function. Transitions between different stages vary in nature and magnitude; likewise, the degree of autonomy among stages enabled by these transitions can vary as well. Because the selective value of traits is likely to shift over ontogeny, the degree of autonomy among stages is important for understanding how processes at one life-history stage alter the conditions for performance and selection at others. We pose 3 questions that help to define a research focus on processes that integrate function across life cycles. First, to what extent do particular transitions between life-history stages allow those stages to function as autonomous units? We identify the roles that stages play in the life history, types of transitions between stages, and 3 forces (structural, genetic/epigenetic, and experiential) that can contribute to integration among stages. Second, what are the potential implications of integration across life cycles for assumptions and predictions of life-history theory? We provide 3 examples where theory has traditionally focused on processes acting within stages in isolation from others. Third, what are the long-term consequences of carryover of experience from one life cycle stage to the next? We distinguish 3 scenarios: persistence (effects of prior experience persist through subsequent stages), amplification (effects persist and are magnified at subsequent stages), and compensation (effects are compensated for and diminish at subsequent stages). We use these scenarios to differentiate between effects of a carryover of state and carryover into subsequent processes. The symposium introduced by our discussion is meant to highlight how discrete stages can be functionally coupled, such that life cycle evolution becomes a more highly integrated response to selection than can be deduced from the study of individual stages.

Estradiol Replacement Reverses Ovariectomy-induced Muscle Contractile and Myosin Dysfunction in Mature Female Mice

Journal of Applied Physiology (Bethesda, Md. : 1985). Apr, 2007  |  Pubmed ID: 17218423

Skeletal muscle contractility and myosin function decline following ovariectomy in mature female mice. In the present study we tested the hypothesis that estradiol replacement can reverse those declines. Four-month-old female C57BL/6 mice (n = 69) were ovariectomized (OVX) or sham operated. Some mice were treated immediately with placebo or 17beta-estradiol (OVX + E(2)) while other mice were treated 30 days postsurgery. Thirty or sixty days postsurgery, soleus muscles were assessed in vitro for contractile function and susceptibility to eccentric contraction-induced injury. Myosin structural dynamics was analyzed in extensor digitorum longus (EDL) muscles by electron paramagnetic resonance spectroscopy. Maximal isometric tetanic force was affected by estradiol status (P < 0.001) being approximately 10% less in soleus muscles from OVX compared with sham-operated mice [168 mN (SD 16.7) vs. 180 mN (SD 14.4)] and was restored in OVX + E(2) mice [187 mN (SD 17.6)]. The fraction of strong-binding myosin during contraction was also affected (P = 0.045) and was approximately 15% lower in EDL muscles from OVX compared with OVX + E(2) mice [0.263 (SD 0.034) vs. 0.311 (SD 0.022)]. Plasma estradiol levels were correlated with maximal isometric tetanic force (r = 0.458; P < 0.001) and active stiffness (r = 0.329; P = 0.044), indicating that circulating estradiol influenced muscle and myosin function. Estradiol was not effective in protecting muscle against an acute eccentric contraction-induced injury (P >or= 0.401) but did restore ovariectomy-induced increases in muscle wet mass caused by fluid accumulation. Collectively, estradiol had a beneficial effect on female mouse skeletal muscle.

Oxygen in Egg Masses: Interactive Effects of Temperature, Age, and Egg-mass Morphology on Oxygen Supply to Embryos

The Journal of Experimental Biology. Feb, 2007  |  Pubmed ID: 17267657

Embryos of many marine invertebrates are encased in gelatinous masses for part or all of development. Because gel and intervening embryos retard oxygen flux, such a life-history mode profoundly affects partial pressures of metabolic gases surrounding embryos. However, little is known about relationships between egg-mass structure and the opportunities and constraints imposed on structure by metabolic gas transport. We examined the effects of four factors (temperature, embryo age, embryo density and egg-mass size) on the metabolism of egg masses using both natural egg masses of a nudibranch and artificial egg masses made from sand dollar embryos and low-melting point agarose. Both temperature and embryo age strongly affected metabolic rates of nudibranch embryos. For embryos of a given age (stage), rates of oxygen consumption roughly doubled between 12 and 21 degrees C; from early cleavage to the veliger stage, consumption rose two- to fourfold, depending on temperature. Oxygen profiles in egg masses showed that advanced embryonic age, and to a lesser extent high temperature, both led to steeper oxygen gradients into egg masses. Egg masses containing advanced embryos at 21 degrees C had very low central oxygen levels. Small-diameter artificial masses (2 mm diameter) had virtually no internal oxygen gradients regardless of embryo density or temperature, while medium (4 mm) and large diameter (10 mm) artificial masses had oxygen profiles that depended strongly and interactively on embryo density and temperature. Together, our data on natural and artificial egg masses suggest that (i) multiple factors have strong effects on metabolic rate; (ii) rates of oxygen transport are relatively invariant with temperature in simple, artificial systems but may vary more strongly with temperature in natural egg masses; and (iii) the four factors--temperature, embryo age, embryo density and egg-mass size--interact in important ways bearing on egg mass design. A simple mathematical model is developed to provide a quantitative means of estimating primary and interactive effects of the different factors. We also show that in T. diomedea the gel itself is the main barrier to oxygen transport into egg masses, and that the metabolic activity of embryos increases substantially when embryos are artificially released from the capsules that contain them within the gel mass.

Estradiol and Tamoxifen Reverse Ovariectomy-induced Physical Inactivity in Mice

Medicine and Science in Sports and Exercise. Feb, 2007  |  Pubmed ID: 17277588

Decreased physical activity and increased body mass are associated with estrogen deficiency.

How Does Metabolic Rate Scale with Egg Size? An Experimental Test with Sea Urchin Embryos

The Biological Bulletin. Apr, 2007  |  Pubmed ID: 17438206

The consequences of changes in egg size for the development of marine invertebrates have been the subject of much theoretical and experimental work. Models that explore larval developmental modes in the context of maternal investment per offspring are often couched in an energetic framework, but the relationships between egg size and the energetics of larval development are poorly understood. We used blastomere separations to examine how experimental reductions in egg size affected (1) larval metabolic rate and (2) larval resistance to starvation. We found that separating blastomeres at the 2- and 4-cell stage resulted in average reductions of 50% and 75%, respectively, in larval metabolic rate. This suggests that, in an experimental context, mass-specific metabolic rate does not change with egg size. We also found that a 50% reduction in egg volume did not reduce the resistance of larvae to starvation when particulate food was withheld. This suggests that the material supplied to larvae in the egg is used primarily for construction of the larval body, rather than as a buffer against starvation or as a means of reducing reliance on exogenous fuel to sustain maintenance metabolism.

Voluntary Run Training but Not Estradiol Deficiency Alters the Tibial Bone-soleus Muscle Functional Relationship in Mice

American Journal of Physiology. Regulatory, Integrative and Comparative Physiology. Nov, 2007  |  Pubmed ID: 17881616

The study's objective was to investigate how estrogen deficiency and run training affect the tibial bone-soleus muscle functional relationship in mice. Female mice were assigned into one of two surgical conditions, ovariectomy (OVX) or sham ovariectomy (sham), and one of two activity conditions, voluntary wheel running (Run) or sedentary (Sed). To determine whether differences observed between OVX and sham conditions could be attributed to estradiol (E(2)), additional OVX mice were supplemented with E(2). Tibial bones were analyzed for their functional capacities, ultimate load, and stiffness. Soleus muscles were analyzed for their functional capacities, maximal isometric tetanic force (P(o)), and peak eccentric force. The ratios of bone functional capacities to those of muscle were calculated. The bone functional capacities were affected by both surgical condition and activity but more strongly by surgical condition. Ultimate load and stiffness for the sham group were 7-12% greater than those for OVX animals (P = 0.002), whereas only stiffness was greater for Run than for Sed animals (9%; P = 0.015). The muscle functional capacities were affected by both surgical condition and activity; however, in contrast to the bone, the muscle was more affected by activity. P(o) and peak eccentric force were 10-21% greater for Run than for Sed animals (P < or = 0.016), whereas only P(o) was greater in sham than in OVX animals (9%; P = 0.011). The bone-to-muscle ratios of functional capacities were affected by activity but not by surgical condition or E(2) supplementation. Thus a mismatch of bone-muscle function occurred in mice that voluntarily ran on wheels, irrespective of estrogen status.

Oxygen Profiles in Egg Masses Predicted from a Diffusion-reaction Model

The Journal of Experimental Biology. Mar, 2008  |  Pubmed ID: 18281342

We developed a novel diffusion-reaction model to describe spatial and temporal changes in oxygen concentrations in gelatinous egg masses containing live, respiring embryos. We used the model in two ways. First, we constructed artificial egg masses of known metabolic density using embryos of the Antarctic sea urchin Sterechnius neumayeri, measured radial oxygen profiles at two temperatures, and compared our measurements to simulated radial oxygen profiles generated by the model. We parameterized the model by measuring the radius of the artificial masses, metabolic densities (=embryo metabolic rate x embryo density) and oxygen diffusion coefficients at both ambient (-1.5 degrees C) or slightly warmer (+1.5-2 degrees C) temperatures. Simulated and measured radial oxygen profiles were similar, indicating that the model captured the major biological features determining oxygen distributions. Second, we used the model to analyze sources of error in step-change experiments for determining oxygen diffusion coefficients (D), and to determine the suitability of simpler, analytical equations for estimating D. Our analysis indicated that embryo metabolism can lead to large (several-fold) overestimates of D if the analytical equation is fitted to step-down-traces of central oxygen concentration (i.e. external oxygen concentration stepped from some high value to zero). However, good estimates of D were obtained from step-up-traces. We used these findings to estimate D in egg masses of three species of nudibranch molluscs: two Antarctic species (Tritonia challengeriana and Tritoniella belli; -1.5 and +2 degrees C) and one temperate Pacific species (Tritonia diomedea; 12 and 22 degrees C). D for all three species was approximately 8 x 10(-6) cm(2) s(-1), and there was no detectable effect of temperature on estimated D. For the Antarctic species, D in egg masses was 70-90% of its value in seawater of similar temperature.

Temperature-oxygen Interactions in Antarctic Nudibranch Egg Masses

The Journal of Experimental Biology. Mar, 2008  |  Pubmed ID: 18281343

The Southern Ocean is one of the coldest, most stable marine environments on Earth and represents a unique environment for investigating metabolic consequences of low temperature. Here we test predictions of a new diffusion-reaction model of O(2) distributions in egg masses, using egg masses of the Antarctic nudibranch mollusk, Tritonia challengeriana. When warmed from -1.5 degrees to +1.5 degrees C, embryos of T. challengeriana showed large increases in O(2) consumption (Q(10) values of 9.6-30.0). Oxygen electrode measurements in intact masses showed, however, that O(2) levels were high throughout and virtually unaffected by temperature. The model suggested that both effects stemmed from very low metabolic densities in egg masses. Detailed morphological measurements of egg masses of T. challengeriana and a temperate congener, T. diomedea, revealed large differences in structure that may be related to O(2) availability. Egg masses of T. challengeriana were approximately twice as thick. However, the most dramatic effects were observed in embryos: embryos of T. challengeriana were >32 times larger (by volume) than embryos of T. diomedea. Antarctic embryos also were contained singly in large egg capsules ( approximately 500 mum diameter). Consequently, Antarctic embryos occurred at much lower densities, with very low metabolic densities.

A Pilot Surrogate Endpoint Biomarker Study of Celecoxib in Oral Premalignant Lesions

Cancer Prevention Research (Philadelphia, Pa.). Oct, 2008  |  Pubmed ID: 19138978

This study evaluated changes in prostaglandin E(2) (PGE(2)) levels and related biomarkers in oral premalignant lesions (OPL) in response to celecoxib treatment. Twenty-two subjects were enrolled and treated with celecoxib. Pretreatment and 12-week biopsies were done. Subjects whose biopsy showed >or=30% decrease in PGE(2) remained on celecoxib for a total of 12 months when repeat biopsy was done. Biopsies were examined to assess degree of dysplasia, DNA ploidy, and immunohistochemical expression of BCL2, pAKT-Ser473, Ki-67, and CD31 (microvessel density). In 18 paired biopsies available at baseline and 12 weeks, mean normalized PGE(2) levels decreased by 38% (P = 0.002). After 12 months, PGE(2) decreased by 31% (P = 0.340). Twelve biopsies (67%; P = 0.0129) showed improvement in degree of dysplasia after 12 weeks, and 8 of 11 biopsies (73%; P = 0.0703) continued to show an improvement in the degree of dysplasia after 12 months. Trends suggested down-modulation of cyclooxygenase-2 and Ki-67 in some tissues, increased pAKT-Ser473 expression, and an inverse relationship between PGE(2) and BCL2 expression. This study documents the feasibility of measuring potential surrogate endpoint biomarkers of chemopreventive agent response in OPLs. Treatment with celecoxib in subjects with OPLs favorably modulates the primary mediator of cyclooxygenase-2 activity, PGE(2), after 12 weeks.

Treg Cells Meet Their Limit

Nature Immunology. Jun, 2009  |  Pubmed ID: 19448655

Egg Size As a Life History Character of Marine Invertebrates: Is It All It's Cracked Up to Be?

The Biological Bulletin. Jun, 2009  |  Pubmed ID: 19556591

Egg size is one of the most important aspects of the life history of free-spawning marine organisms, and it is correlated with larval developmental mode and many other life-history characters. Egg size is simple to measure and data are available for a wide range of taxa, but we have a limited understanding of how large and small eggs differ in composition; size is not always the best measure of the characters under selection. Large eggs are generally considered to reflect increased maternal investment, but egg size alone can be a poor predictor of energetic content within and among taxa. We review techniques that have been used to measure the energetic content and biochemical makeup of invertebrate eggs and point out the strengths and difficulties associated with each. We also suggest a number of comparative and descriptive approaches to biochemical constituent analysis that would strengthen our understanding of how natural selection shapes oogenic strategies. Finally, we highlight recent empirical research on the intrinsic factors that drive intraspecific variation in egg size. We also highlight the relative paucity of these data in the literature and provide some suggestions for future research directions.

Oxygen Hypothesis of Polar Gigantism Not Supported by Performance of Antarctic Pycnogonids in Hypoxia

Proceedings. Biological Sciences / The Royal Society. Mar, 2009  |  Pubmed ID: 19129117

Compared to temperate and tropical relatives, some high-latitude marine species are large-bodied, a phenomenon known as polar gigantism. A leading hypothesis on the physiological basis of gigantism posits that, in polar water, high oxygen availability coupled to low metabolic rates relieves constraints on oxygen transport and allows the evolution of large body size. Here, we test the oxygen hypothesis using Antarctic pycnogonids, which have been evolving in very cold conditions (-1.8-0 degrees C) for several million years and contain spectacular examples of gigantism. Pycnogonids from 12 species, spanning three orders of magnitude in body mass, were collected from McMurdo Sound, Antarctica. Individual sea spiders were forced into activity and their performance was measured at different experimental levels of dissolved oxygen (DO). The oxygen hypothesis predicts that, all else being equal, large pycnogonids should perform disproportionately poorly in hypoxia, an outcome that would appear as a statistically significant interaction between body size and oxygen level. In fact, although we found large effects of DO on performance, and substantial interspecific variability in oxygen sensitivity, there was no evidence for sizexDO interactions. These data do not support the oxygen hypothesis of Antarctic pycnogonid gigantism and suggest that explanations must be sought in other ecological or evolutionary processes.

Limits to Diffusive O2 Transport: Flow, Form, and Function in Nudibranch Egg Masses from Temperate and Polar Regions

PloS One. 2010  |  Pubmed ID: 20711406

Many aquatic animals enclose embryos in gelatinous masses, and these embryos rely on diffusion to supply oxygen. Mass structure plays an important role in limiting or facilitating O2 supply, but external factors such as temperature and photosynthesis can play important roles as well. Other external factors are less well understood.

Introduction to the Symposium: Advances in Antarctic Marine Biology

Integrative and Comparative Biology. Dec, 2010  |  Pubmed ID: 21558251

T Cell Receptor Signal Strength in Treg and INKT Cell Development Demonstrated by a Novel Fluorescent Reporter Mouse

The Journal of Experimental Medicine. Jun, 2011  |  Pubmed ID: 21606508

The ability of antigen receptors to engage self-ligands with varying affinity is crucial for lymphocyte development. To further explore this concept, we generated transgenic mice expressing GFP from the immediate early gene Nr4a1 (Nur77) locus. GFP was up-regulated in lymphocytes by antigen receptor stimulation but not by inflammatory stimuli. In T cells, GFP was induced during positive selection, required major histocompatibility complex for maintenance, and directly correlated with the strength of T cell receptor (TCR) stimulus. Thus, our results define a novel tool for studying antigen receptor activation in vivo. Using this model, we show that regulatory T cells (T(reg) cells) and invariant NKT cells (iNKT cells) perceived stronger TCR signals than conventional T cells during development. However, although T(reg) cells continued to perceive strong TCR signals in the periphery, iNKT cells did not. Finally, we show that T(reg) cell progenitors compete for recognition of rare stimulatory TCR self-ligands.

TCR Affinity in Thymic Development

Immunology. Dec, 2011  |  Pubmed ID: 22182461

Understanding the thymic processes that support the generation of functionally competent and self-tolerant lymphocytes requires dissection of the T cell receptor (TCR) response to ligands of different affinities. In spatially segregated regions of the thymus, with unique expression of proteases and cytokines, TCR affinity guides a number of cell fate decisions. Yet affinity alone does not explain the selection paradox. Increasing evidence suggests that the 'altered peptide' model of the 1980's together with the affinity model might best explain how the thymus supports conventional and regulatory T cell development. Development of new tools to study the strength of TCR signals perceived by T cells, novel Treg transgenic mice, and tetramer enrichment strategies have provided an insight into the nature of TCR signals perceived during thymocyte development. These topics are discussed and support for the prevailing hypotheses are presented.

Estradiol's Beneficial Effect on Murine Muscle Function is Independent of Muscle Activity

Journal of Applied Physiology (Bethesda, Md. : 1985). Jan, 2011  |  Pubmed ID: 20966194

Estradiol (E₂) deficiency decreases muscle strength and wheel running in female mice. It is not known if the muscle weakness results directly from the loss of E₂ or indirectly from mice becoming relatively inactive with presumably diminished muscle activity. The first aim of this study was to determine if cage activities of ovariectomized mice with and without E₂ treatment differ. Ovariectomized mice were 19-46% less active than E₂-replaced mice in terms of ambulation, jumping, and time spent being active (P ≤ 0.033). After E₂-deficient mice were found to have low cage activities, the second aim was to determine if E₂ is beneficial to muscle contractility, independent of physical activities by the mouse or its hindlimb muscles. Adult, female mice were ovariectomized or sham-operated and randomized to receive E₂ or placebo and then subjected to conditions that should maintain physical and muscle activity at a constant low level. After 2 wk of hindlimb suspension or unilateral tibial nerve transection, muscle contractile function was assessed. Soleus muscles of hindlimb-suspended ovariectomized mice generated 31% lower normalized (relative to muscle contractile protein content) maximal isometric force than suspended mice with intact ovaries (P ≤ 0.049). Irrespective of whether the soleus muscle was innervated, muscles from ovariectomized mice generated ∼20% lower absolute and normalized maximal isometric forces, as well as power, than E₂-replaced mice (P ≤ 0.004). In conclusion, E₂ affects muscle force generation, even when muscle activity is equalized.