Signal transducer and activator of transcription (STAT) proteins are transcription factors that play a critical role in the response of a variety of eukaryotic cells to cytokine and growth factor signaling. In Drosophila, the STAT homolog encoded by the stat92E gene is required for the normal development of multiple tissues, including embryonic segmentation, imaginal discs, blood cells, male germ cells, and sex determination. We used multiple approaches to study the role of stat92E in oogenesis. Stat92E RNA expression is strongest in the differentiating follicle cells in the germarium, as determined by in situ hybridization. We generated an ethylmethane sulfonate-induced, temperature-sensitive allele, stat92E(F), in which the mutant protein contains a P506S substitution, located in the DNA binding domain. At the restrictive temperature, mutant females are sterile. Mutant ovaries have multiple defects, including fused egg chambers and an absence of interfollicular stalks cells and functional polar follicle cells. An analysis of mosaic clones, using an apparent null stat92E allele, indicates that Stat92E is required in the polar/stalk follicle cell lineage. We conclude that stat92E is necessary for the early differentiation of follicle cells and for proper germ line cell encapsulation during Drosophila oogenesis.
The suppressor of position effect variegation (PEV) locus Su-var(3)6 maps to 87B5-10. The breakpoints of deficiencies that define this interval have been placed on a 250-kb molecular map of the region. The locus is allelic to the ck19 complementation group previously shown to encode a type 1 serine-threonine protein phosphatase (PP1) catalytic subunit. When introduced into flies by P element-mediated transformation, a 5.8-kb genomic fragment carrying this gene overcomes the suppressor phenotype of Su-var(3)6(01) and recessive lethality of all mutations of the locus. Four of the mutant alleles at the locus show a broad correlation between high levels of suppression of PEV, a high frequency of aberrant mitosis and low PP1 activity in larval extracts. However, some alleles with low PP1 activity show weak suppression of PEV with a high frequency of abnormal mitosis, whereas others show strong suppression of PEV with normal mitosis. The basis for these discussed.
The localization of oocyte-specific determinants in the form of mRNAs to the pro-oocyte is essential for the establishment of oocyte identity. Localization of the Bicaudal-D (Bic-D) protein to the presumptive oocyte is required for the accumulation of Bic-D and other mRNAs to the pro-oocyte. The Bic-D protein contains four well-defined heptad repeat domains characteristic of intermediate filament proteins, and several of the mutations in Bic-D map to these conserved domains. We have undertaken a structure-function analysis of Bic-D by testing the function of mutant Bic-D transgenes (Bic-DH) deleted for each of the heptad repeat domains in a Bic-D null background. Our transgenic studies indicate that only the C-terminal heptad repeat deletion results in a protein that has lost zygotic and ovarian functions. The three other deletions result in proteins with full zygotic function, but with affected ovarian function. The functional importance of each domain is well correlated with its conservation in evolution. The analysis of females heterozygous for Bic-DH and the existing alleles Bic-DPA66 or Bic-DR26 reveals that Bic-DR26 as well as some of Bic-DH transgenes have antimorphic effects. The yeast two-hybrid interaction assay shows that Bic-D forms homodimers. Furthermore, we found that Bic-D exists as a multimeric protein complex consisting of Egl and at least two Bic-D monomers.
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