We have isolated and characterized the will die slowly (wds) gene of Drosophila melanogaster, formerly known as l(1)zw8 or l(1)3Ad. The gene codes for a 2.0-kb RNA that is transcribed at all stages of development. The RNA has been localized by in situ hybridization to imaginal discs, larval brain, to nurse cells in the ovary, and to spermatogonia and spermatocytes in the testis. The putative translation product contains seven WD-repeats and is, therefore, a new member of the family of WD-proteins. Clear homologues of the Drosophila WDS protein exist in three other fully sequenced higher eukaryotes - human, Caenorhabditis elegans and Arabidopsis. A genomic fragment containing the wds transcription unit is able to rescue two different lethal wds alleles, thus proving that we have indeed isolated the wds gene.
Oogenesis in Drosophila is a useful model for studying cell differentiation. We have analyzed the role of the egh gene in these processes with the aid of a newly isolated viable but female sterile allele. This mutation results in diverse variable defects in oogenesis. The most frequent defect being follicles that have either more or less than the normal number of 16 germ cells. This is caused by erroneous splitting and/or fusion of correct clusters of 16 cystocytes. The entire follicle has a rather flexible structure in this allele, most obvious by a highly variable position of the oocyte within the follicle. Moreover, a second oocyte can also develop in egh clusters. This is exclusively observed in aberrant follicles that are generated by the aforementioned splitting/fusion process. Surprisingly, even a germ cell which is distinct from the two pro-oocytes can differentiate into an oocyte under these circumstances. Hence, determination of the oocyte is definitely not fixed when germ cell clusters are enveloped by prefollicular cells, and interactions between follicle cells and germ cells must play an important role in oocyte specification. Molecular analysis proves that the oocyte-specific transcript of the egh gene is drastically reduced in this viable allele.
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