dissection-and-culture-of-mouse-embryonic-kidney

Dissection and Culture of Mouse Embryonic Kidney

The goal of this protocol is to describe a method for the dissection, isolation, and culture of mouse metanephric rudiments. 
During mammalian kidney ...

Uppsala University

The development of connections between thalamic afferents and their cortical target cells occurs in a highly precise manner. Thalamic axons enter the cortex through deep cortical layers, then stop their growth in layer 4 and elaborate terminal arbors specifically within this layer. The mechanisms that underlie target layer recognition for thalamocortical projections are not known. We compared the growth pattern of thalamic explants cultured on membrane substrates purified from cortical layer 4, the main recipient layer for thalamic axons, and cortical layer 5, a non-target layer. Thalamic axons exhibited a reduced growth rate and an increased branching density on their appropriate target membranes compared with non-target substrate. When confronted with alternating stripes of both membrane substrates, thalamic axons grew preferentially on their target membrane stripes. Enzymatic treatment of cortical membranes revealed that growth, branching and guidance of thalamic axons are independently regulated by attractive and repulsive cues differentially expressed in distinct cortical layers. These results indicate that multiple membrane-associated molecules collectively contribute to the laminar targeting of thalamic afferents. Furthermore, we found that interfering with the function of Eph tyrosine kinase receptors and their ligands, ephrins, abolished the preferential branching of thalamic axons on their target membranes, and that recombinant ephrin-A5 ligand elicited a branch-promoting activity on thalamic axons. We conclude that interactions between Eph receptors and ephrins mediate branch formation of thalamic axons and thereby may play a role in the establishment of layer-specific thalamocortical connections.

Ephrins regulate the formation of terminal axonal arbors during the development of thalamocortical projections.

The functional architecture of the cerebral cortex is based on intrinsic connections that precisely link neurons from distinct cortical laminae as well as layer-specific afferent and efferent projections. Experimental strategies using in vitro assays originally developed by Friedrich Bonhoeffer have suggested that positional cues confined to individual layers regulate the assembly of local cortical circuits and the formation of thalamocortical projections. One of these wiring molecules is ephrinA5, a ligand for Eph receptor tyrosine kinases. EphrinA5 and Eph receptors exhibit highly dynamic expression patterns in distinct regions of the cortex and thalamus during early and late stages of thalamocortical and cortical circuit formation. In vitro assays suggest that ephrinA5 is a multifunctional wiring molecule for different populations of cortical and thalamic axons. Additionally, the expression patterns of ephrinA5 during cortical development are consistent with this molecule regulating, in alternative ways, specific components of thalamic and cortical connectivity. To test this directly, the organization of thalamocortical projections was examined in mice lacking ephrinA5 gene expression. The anatomical studies in ephrinA5 knockout animals revealed a miswiring of limbic thalamic projections and changes in neocortical circuits that were predicted from the expression pattern and the in vitro analysis of ephrinA5 function.

Multiple roles of ephrins during the formation of thalamocortical projections: maps and more.

The complex task of wiring up the brain during embryonic development is achieved by a multitude of guidance signals acting in complex combinations to drive growing axons to their proper targets. The somatosensory system provides an extensively studied model system featuring many universal mechanisms of neural development. In rodents, it constitutes an important model to study how precise topographic connections are achieved. Recent evidence suggests that the Eph/ephrin family of guidance molecules is of pivotal importance for the development of the somatosensory system. Members of Eph/ephrin family are thought to be involved in the global presorting of thalamic axons projecting to the cortex, in labeling specific cortical areas for innervation, in providing topographic cues within the target area, and in distinguishing cortical layers for intracortical wiring. The Eph/ephrin system also seems to contribute to the formation of specific corticothalamic feedback projections. So far, the functions of only a few members of the Eph/ephrin family have been examined, but expression analysis indicates complex combinatorial effects of these signaling molecules. Understanding the Eph/ephrin wiring code is expected to yield new insights into the development and plasticity of brain circuits involved in higher functions.

Connecting thalamus and cortex: the role of ephrins.

The role of wiring molecules in circuit assembly is tested directly in genetically engineered animals, in which the corresponding gene has been selectively mutated. Minor alterations in neuronal circuits in these mutant animals are explained by redundancy and/or adaptive changes of other genes relevant for brain development. There is very little known, however, about the extent and nature of the compensatory molecular mechanisms. Using gene microarrays, we compared gene expression patterns in the somatosensory cortex of wild type and ephrinA5 deficient mice, which exhibit subtle, but highly reproducible alterations of thalamocortical projections and intrinsic cortical circuits. We found that between 2.2%-5.7% of all transcripts (140-373 targets) detected in the somatosensory cortex are differentially expressed in comparing wild type and ephrinA5 mutants. A gene group analysis of the annotated transcripts revealed that a high proportion of the dysregulated genes encode proteins relevant for circuit development. Finer grain analysis by in situ hybridization and quantitative RT-PCR revealed that 20% of the Eph/ephrin family genes expressed in the somatosensory cortex are up-regulated in the mutant. One of these genes, EphB6, was up-regulated in all cortical layers, where it is normally expressed. However, the ephrinA2 and EphA5 were up-regulated only in selected layers in the cortex of the mutant; expression levels in other layers did not change. These findings indicate that there is specificity of adaptive and compensative changes in gene expression after the mutation of a single gene relevant for cortical development. Our results also point to the complexity of interpreting phenotypes of gene knock-out animals.

Adaptive changes in gene expression patterns in the somatosensory cortex after deletion of ephrinA5.

Hearing requires an optimal afferent innervation of sensory hair cells by spiral ganglion neurons in the cochlea. Here we report that complementary expression of ephrin-A5 in hair cells and EphA4 receptor among spiral ganglion neuron populations controls the targeting of type I and type II afferent fibres to inner and outer hair cells, respectively. In the absence of ephrin-A5 or EphA4 forward signalling, a subset of type I projections aberrantly overshoot the inner hair cell layer and invade the outer hair cell area. Lack of type I afferent synapses impairs neurotransmission from inner hair cells to the auditory nerve. By contrast, radial shift of type I projections coincides with a gain of presynaptic ribbons that could enhance the afferent signalling from outer hair cells. Ephexin-1, cofilin and myosin light chain kinase act downstream of EphA4 to induce type I spiral ganglion neuron growth cone collapse. Our findings constitute the first identification of an Eph/ephrin-mediated mutual repulsion mechanism responsible for specific sorting of auditory projections in the cochlea.

Ephrin-A5/EphA4 signalling controls specific afferent targeting to cochlear hair cells.

Experimental hydronephrosis induced by partial ureteral obstruction at 3 wk of age causes hypertension and renal impairment in adult rats and mice. Signaling by Ephrin receptors (Eph) and their ligands (ephrins) importantly regulates embryonic development. Genetically modified mice, where the cytoplasmic domain of the EphA4 receptor has been substituted by enhanced green fluorescent protein (EphA4gf/gf), develop spontaneous hydronephrosis and provide a model for further studies of the disorder. The present study aimed to determine if animals with congenital hydronephrosis develop hypertension and renal injuries, similar to that of experimental hydronephrosis. Ultrasound and Doppler techniques were used to visualize renal impairment in the adult mice. Telemetric blood pressure measurements were performed in EphA4gf/gf mice and littermate controls (EphA4+/+) during normal (0.7% NaCl)- and high (4% NaCl)-sodium conditions. Renal excretion, renal plasma flow, and glomerular filtration were studied, and histology and morphology of the kidneys and ureters were performed. EphA4gf/gf mice developed variable degrees of hydronephrosis that correlated with their blood pressure level. In contrast to EphA4+/+, the EphA4gf/gf mice displayed salt-sensitive hypertension, reduced urine concentrating ability, reduced renal plasma flow, and lower glomerular filtration rate. Kidneys from EphA4gf/gf mice showed increased renal injuries, as evidenced by fibrosis, inflammation, and glomerular and tubular changes. In conclusion, congenital hydronephrosis causes hypertension and renal damage, similar to that observed in experimentally induced hydronephrosis. This study further reinforces the supposed causal link between hydronephrosis and later development of hypertension in humans.

Impaired EphA4 signaling leads to congenital hydronephrosis, renal injury, and hypertension.

The neuromodulatory transmitters, biogenic amines, have profound effects on multiple neurons and are essential for normal behavior and mental health. Here we report that the orphan transporter SLC10A4, which in the brain is exclusively expressed in presynaptic vesicles of monoaminergic and cholinergic neurons, has a regulatory role in dopamine homeostasis.

SLC10A4 is a vesicular amine-associated transporter modulating dopamine homeostasis.

Quaking (QKI) is an RNA-binding protein involved in post-transcriptional mRNA processing. This gene is found to be associated with several human neurological disorders. Early expression of QKI proteins in the developing mouse neuroepithelium, together with neural tube defects in Qk mouse mutants, suggest the functional requirement of Qk for the establishment of the nervous system. As a knockout of Qk is embryonic lethal in mice, other model systems like the zebrafish could serve as a tool to study the developmental functions of qki. In the present study we sought to characterize the evolutionary relationship and spatiotemporal expression of qkia, qki2, and qkib; zebrafish homologs of human QKI. We found that qkia is an ancestral paralog of the single tetrapod Qk gene that was likely lost during the fin-to-limb transition. Conversely, qkib and qki2 are orthologs, emerging at the root of the vertebrate and teleost lineage, respectively. Both qki2 and qkib, but not qkia, were expressed in the progenitor domains of the central nervous system, similar to expression of the single gene in mice. Despite having partially overlapping expression domains, each gene has a unique expression pattern, suggesting that these genes have undergone subfunctionalization following duplication. Therefore, we suggest the zebrafish could be used to study the separate functions of qki genes during embryonic development.

Characterization and Expression of the Zebrafish qki Paralogs.

Quaking (QKI) is a gene exclusively expressed within glial cells. QKI has previously been implicated in various neurological disorders and diseases, including Alzheimer's disease (AD), a condition for which increasing evidence suggests a central role of glia cells. The objective of the present study was to investigate the expression levels of QKI and three QKI isoforms (QKI5, QKI6, and QKI7) in AD. Genes that have previously been related to the ontogeny and progression of AD, specifically APP, PSEN1, PSEN2, and MAPT, were also investigated. A real-time PCR assay of 123 samples from human postmortem sporadic AD patients and control brains was performed. The expression values were analyzed with an analysis of covariance model and subsequent multiple regressions to explore the possibility of related expression values between QKI, QKI isoforms, and AD-related genes. Further, the sequences of AD-related genes were analyzed for the presence of QKI binding domains. QKI and all measured QKI isoforms were found to be significantly upregulated in AD samples, relative to control samples. However, APP, PSEN1, PSEN2, and MAPT were not found to be significantly different. QKI and QKI isoforms were found to be predictive for the variance of APP, PSEN1, PSEN2, and MAPT, and putative QKI binding sites suggests an interaction with QKI. Overall, these results implicate a possible role of QKI in AD, although the exact mechanism by which this occurs remains to be uncovered.

Gene Expression of Quaking in Sporadic Alzheimer's Disease Patients is Both Upregulated and Related to Expression Levels of Genes Involved in Amyloid Plaque and Neurofibrillary Tangle Formation.

A substantial portion of the human population is affected by urogenital birth defects resulting from a failure in ureter development. Although recent research suggests roles for several genes in facilitating the ureter/bladder connection, the underlying molecular mechanisms remain poorly understood. Signaling via Eph receptor tyrosine kinases is involved in several developmental processes. Here we report that impaired Eph/Ephrin signaling in genetically modified mice results in severe hydronephrosis caused by defective ureteric bud induction, ureter maturation, and translocation. Our data imply that ureter translocation requires apoptosis in the urogenital sinus and inhibition of proliferation in the common nephric duct. These processes were disturbed in EphA4/EphB2 compound knockout mice and were accompanied by decreased ERK-2 phosphorylation. Using a set of Eph, Ephrin, and signaling-deficient mutants, we found that during urogenital development, different modes of Eph/Ephrin signaling occur at several sites with EphrinB2 and EphrinA5 acting in concert. Thus, Eph/Ephrin signaling should be considered in the etiology of congenital kidney and urinary tract anomalies.

Multimodal Eph/Ephrin signaling controls several phases of urogenital development.

Mast cells act as sensors in innate immunity and as effector cells in adaptive immune reactions. Here we demonstrate that SLC10A4, also referred to as the vesicular aminergic-associated transporter, VAAT, modifies mast cell degranulation. Strikingly, Slc10a4 (-/-) bone marrow-derived mast cells (BMMCs) had a significant reduction in the release of granule-associated mediators in response to IgE/antigen-mediated activation, whereas the in vitro development of mast cells, the storage of the granule-associated enzyme mouse mast cell protease 6 (mMCP-6), and the release of prostaglandin D2 and IL-6 were normal. Slc10a4-deficient mice had a strongly reduced passive cutaneous anaphylaxis reaction and a less intense itching behaviour in response to the mast cell degranulator 48/80. Live imaging of the IgE/antigen-mediated activation showed decreased degranulation and that ATP was retained to a higher degree in mast cell granules lacking SLC10A4. Furthermore, ATP was reduced by two thirds in Slc10a4 (-/-) BMMCs supernatants in response to IgE/antigen. We speculate that SLC10A4 affects the amount of granule-associated ATP upon IgE/antigen-induced mast cell activation, which affect the release of granule-associated mast cell mediators. In summary, SLC10A4 acts as a regulator of degranulation in vitro and of mast cell-related reactions in vivo.

Article	Year
Ephrins regulate the formation of terminal axonal arbors during the development of thalamocortical projections. Development (Cambridge, England)\| PubMed ID: 12135931	2002
Multiple roles of ephrins during the formation of thalamocortical projections: maps and more. Journal of neurobiology\| PubMed ID: 15007829	2004
Connecting thalamus and cortex: the role of ephrins. The anatomical record. Part A, Discoveries in molecular, cellular, and evolutionary biology\| PubMed ID: 16411249	2006
Adaptive changes in gene expression patterns in the somatosensory cortex after deletion of ephrinA5. Molecular and cellular neurosciences\| PubMed ID: 18619851	2008
Ephrin-A5/EphA4 signalling controls specific afferent targeting to cochlear hair cells. Nature communications\| PubMed ID: 23385583	2013
Impaired EphA4 signaling leads to congenital hydronephrosis, renal injury, and hypertension. American journal of physiology. Renal physiology\| PubMed ID: 23637205	2013
SLC10A4 is a vesicular amine-associated transporter modulating dopamine homeostasis. Biological psychiatry\| PubMed ID: 25176177	2015
Characterization and Expression of the Zebrafish qki Paralogs. PloS one\| PubMed ID: 26727370	2016
Gene Expression of Quaking in Sporadic Alzheimer's Disease Patients is Both Upregulated and Related to Expression Levels of Genes Involved in Amyloid Plaque and Neurofibrillary Tangle Format... Journal of Alzheimer's disease : JAD\| PubMed ID: 27163826	2016
Multimodal Eph/Ephrin signaling controls several phases of urogenital development. Kidney international\| PubMed ID: 27344203	2016
SLC10A4 regulates IgE-mediated mast cell degranulation in vitro and mast cell-mediated reactions in vivo. Scientific reports\| PubMed ID: 28439090	2017

Christiane Peuckert

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