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Articles by John H. Yoder in JoVE
JoVE General
Дрозофилы куколки Живот Immunohistochemistry
Department of Biological Sciences, University of Alabama
Антитела окрашивание
Other articles by John H. Yoder on PubMed
Modulation of KSR Activity in Caenorhabditis Elegans by Zn Ions, PAR-1 Kinase and PP2A Phosphatase
Vulval differentiation in Caenorhabditis elegans is controlled by a conserved signal transduction pathway mediated by Ras and a kinase cascade that includes Raf, Mek and MAPK. Activation of this cascade is positively regulated by a number of proteins such as KSR (kinase suppressor of Ras), SUR-8/SOC-2, SUR-6/PP2A-B and CDF-1. We describe the functional characterization of sur-7 and several genes that regulate signaling downstream of ras. We identified sur-7 by isolating a mutation that suppresses an activated ras allele, and showed that SUR-7 is a divergent member of the cation diffusion facilitator family of heavy metal ion transporters that is probably localized to the endoplosmic recticulum membrane and regulates cellular Zn(2+) concentrations. Genetic double mutant analyses suggest that the SUR-7-mediated effect is not a general toxic response. Instead, Zn(2+) ions target a specific step of the pathway, probably regulation of the scaffolding protein KSR. Biochemical analysis in mammalian cells indicates that high Zn(2+) concentration causes a dramatic increase of KSR phosphorylation. Genetic analysis also indicates that PP2A phosphatase and PAR-1 kinase act downstream of Raf to positively and negatively regulate KSR activity, respectively.
The Evolution of Abdominal Reduction and the Recent Origin of Distinct Abdominal-B Transcript Classes in Diptera
In insects, the Hox gene Abdominal-B (Abd-B) governs the development of the posterior-most segments, the number and fate of which differ within and between orders. A striking feature of insect evolution is a trend toward the reduction of posterior abdominal segments which is most pronounced in higher Diptera. In Drosophila melanogaster, two distinct Abd-B transcript classes and protein isoforms are expressed in non-overlapping domains and have discrete functions in patterning the posterior abdomen. It has been proposed that evolutionary changes in Abd-B structure and expression are responsible for the reduction of the dipteran abdomen. We have investigated the relationship between the evolution of the Abd-B gene and abdominal reduction by analyzing the structure and expression of homologs from four additional dipterans representing distinct clades within the order. The lower dipteran mosquito Anopheles gambiae expresses a single Abd-B transcript class, as do two species phylogenetically intermediate to mosquitoes and drosophilids. These results delimit the evolution of distinct functional Abd-B isoforms to within the dipteran radiation after the origin of the reduced abdominal morphology. Furthermore, we found that the spatial distribution of Abd-B transcripts in non-drosophilid Diptera is identical to the combined domains of the two D. melanogaster Abd-B transcripts. Therefore, neither the structural evolution nor changes in the spatial regulation of Abd-B account for the derived abdomen of higher Diptera. The recent subfunctionalization of this Hox gene has occurred without any apparent morphological correlate. We conclude that regulatory modifications to developmental programs downstream of or parallel to Abd-B are responsible for the evolutionary reduction of the higher dipteran postabdomen.
Sexually Dimorphic Regulation of the Wingless Morphogen Controls Sex-specific Segment Number in Drosophila
Sexual dimorphism is widespread throughout the metazoa and plays important roles in mate recognition and preference, sex-based niche partitioning, and sex-specific coadaptation. One notable example of sex-specific differences in insect body morphology is presented by the higher diptera, such as Drosophila, in which males develop fewer abdominal segments than females. Because diversity in segment number is a distinguishing feature of major arthropod clades, it is of fundamental interest to understand how different numbers of segments can be generated within the same species. Here we show that sex-specific and segment-specific regulation of the Wingless (Wg) morphogen underlies the development of sexually dimorphic adult segment number in Drosophila. Wg expression is repressed in the developing terminal male abdominal segment by the combination of the Hox protein Abdominal-B (Abd-B) and the sex-determination regulator Doublesex (Dsx). The subsequent loss of the terminal male abdominal segment during pupation occurs through a combination of developmental processes including segment compartmental transformation, apoptosis, and suppression of cell proliferation. Furthermore, we show that ectopic expression of Wg is sufficient to rescue this loss. We propose that dimorphic Wg regulation, in concert with monomorphic segment-specific programmed cell death, are the principal mechanisms of sculpting the sexually dimorphic abdomen of Drosophila.
