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Sequencing cDNA and genomic DNA from the ovarian tumor gene revealed a gene with seven introns spanning 4.5 kilobases. The proline-rich, hydrophilic otu protein is novel. An antibody prepared to a jI-gal-otu fusion protein recognized a 110-kilodalton ovarian protein which was altered in the ovaries of otu gene mutants.The ovarian tumor (otu) gene product is required throughout oogenesis for the development of the female germ line (23). The 20 recessive female-sterile alleles of otu are classified into three categories according to the severity of their phenotypes. Ovaries from quiescent homozygotes exhibit little or no mitotic proliferation of the germ cells. Ovaries from oncogenic homozygotes undergo uncontrolled germ cell proliferation with failure of these cells to differentiate. The homozygous differentiated ovaries contain partially to fully differentiated nurse cells, oocytes, or both (21,22,32,41).While the oncogenic and differentiated alleles fail to complement the severe quiescent alleles to fertility, some heteroallelic combinations are fertile. The best example is the oncogenic/differentiated combination, otu11lotu14, which is fully fertile (40), suggesting that there could be more than one otu gene product (41) or that the product associates with itself (40) or with other molecules.Recently, we showed that the otu gene hybridizes to a moderately abundant ovarian transcript of 3.2 kilobases (kb) (32). Minor ovarian RNAs of 3.8 and 4.0 kb were also detected in ovaries at a much lower abundance, and a different set of transcripts hybridizing to the otu gene were found in testis RNA and are also at a low abundance (about 2% of the 3.2-kb ovarian transcript; 32).As a first step towards understanding the biochemical function of the otu gene product during oogenesis, we have sequenced the otu gene and a cDNA containing the entire coding sequence of the protein.To isolate an otu cDNA clone for sequencing, an ovarian cDNA library was prepared by using poly(A)+ RNA isolated from hand-dissected ovaries of Canton S flies (1, 32) which represented all stages of oogenesis. The cDNA library was prepared (15) by oligo(dT) priming, EcoRI linkers (sequence CCGAATTCGG) were added, and 2 x 106 recombinants were packaged in the expression vector lambda gtll (19). The unamplified library (250,000 plaques) was screened (4) with radiolabeled probes (35). In the first screen, a probe generated to the 3.2-kb EcoRI fragment was used, since it hybridizes strongly to otu RNA (32; Fig. 1). The second and third screens were carried out by using the upstream 1.0-kb EcoRI fragment (32; Fig. 1 with more 5' sequences. Since the 1.0-kb EcoRI fragment hybridizes less efficiently to the 3.2-kb otu RNA on Northern (RNA) blots (32), we reasoned that the transcription unit may only extend a short way into this fragment. We identified 50 positives (0.02%), rescreened 25 of them with the 1.0-kb EcoRI fragment, and recovered two clones.The cDNAs and genomic DNAs (identified previously [32] and from a Canton S library [28]) were subcloned into ...

Drosophila has evolved a highly efficient means of synthesizing the large quantities of mRNA and protein required in early embryogenesis prior to the onset of zygotic transcription. The adaptation involves the generation of an egg chamber consisting of an oocyte and 15 germ-line-derived nurse cells that are connected to one another by cytoplasmic bridges. The nurse cells perform a trophic function, that is, their polyploidization dramatically increases the synthetic capacity within the egg chamber. The basic structure of an egg chamber is laid down in the germarium: The daughter of a stem cell (a cystoblast) proceeds through 4 successive and incomplete mitotic divisions to generate a 16 cell cyst, which is then surrounded by a layer of somatically derived follicle cells. The 16 cells or cystocytes are connected in a specific arrangement by structures termed ring canals (King et al. 1956;Brown and King 1964;Kinderman and King 1973); one cystocyte will develop as an oocyte, and the remaining 15 differentiate as nurse cells. Before the egg chamber leaves the germarium and enters the vitellarium, mitotic germ cell division within the egg chamber ceases and differentiation of cystocytes is initiated. 'Present address:

Genomic sequences controlling follicle cell‐specific amplification of the X‐linked Drosophila chorion gene cluster were mapped by P element‐mediated transformation. Several DNA fragments containing the s38 gene and flanking sequences induced tissue‐specific amplification, although replication levels were subject to position effects. Deletion analysis identified a 467‐bp region upstream from the s38 transcription start site that contained sequences essential in cis for amplification. The essential region shared 32 bp of imperfect sequence homology with a previously identified region necessary for third chromosome chorion gene cluster amplification. This homologous segment contained a repetitive motif consisting of perfect and imperfect AATAC repeats; it was localized near the boundary of the essential domain since most, but not all, the repeats could be deleted without eliminating transposon‐induced amplification. The repetitive region was not required for developmentally regulated s38 transcription, therefore our results identified at least one element required for amplification but not for chorion gene transcription. The homologous repetitive sequences within the amplification‐essential regions may constitute part of the replication origins used to differentially replicate the two chorion domains during oogenesis.