No abstract

DNA replication patterns in the nurse and follicle cells of wild type and a female sterile mutant, fs(1)1304, of Drosophila melanogaster have been studied by DNA-Feulgen cytophotometry, using a cell dispersal technique that allowed the measurement of DNA amounts in individual nuclei from egg chambers of known developmental stages. DNA-Feulgen values associated with various ovarian nuclei from egg chambers at different stages of development were used to assess a base line DNA content for ovarian tissues and to estimate the extent of DNA replication in the nurse cells and follicle cells of growing and mature egg chambers. Our data show that both the nurse and follicle cells undergo multiple cycles of endonuclear DNA replication and that there may be selective amplification as well as underreplication by portions of the genome in these highly polyploid, ovarian cells. Alternative models are proposed to account for the DNA replication patterns observed. Comparisons of DNA-Feulgen levels in wild type ovarian nuclei with those found for the fs(1)1304 mutant and its heterozygote in the balanced stock fs/FM3, show that equivalent DNA levels are present in follicle cell nuclei from all three types of females. Nurse cell nuclei in the homozygous fs stock, however, fail to achieve the same high DNA levels observed in both fs/FM3 and wild type nurse cell nuclei. Although the nuclei of follicle cells in ovaries from fs/fs females appear morphologically like those surrounding egg chambers in wild type ovaries, nurse cell nuclei from mutant females show a more compacted organization of their chromatin than found for nurse cell nuclei from wild type ovaries at similar developmental stages. Our findings suggest that a major effect of the fs(1)1304 mutation may be on the coiling behavior of chromatin and the conformation of DNA-protein moieties in both nurse cell and follicle cell nuclei. These changes in chromatin structure apparently are manifest by perturbations in DNA replication patterns and normal gene function in these biosynthetically active cells.

The amounts of DNA in haploid and diploid cells of Drosophila melanogaster have been determined by DNA-Feulgen cytophotometry, using Xenopus laevis erythrocyte nuclei as a reference standard. The haploid male genome is estimated to be 0.18 pg DNA and the haploid female genome, 0.20 pg DNA.

No abstract

The female-sterile ovarian tumor gene, otu, is located in cytological region 7F1 on the Drosophila melanogaster chromosome map. We have mapped the gene at the molecular level by using four dysgenic alleles and two revertant derivatives of these alleles as well as an ethyl methanesulfonate-induced allele. The insertional (dysgenic) changes were all associated with one restriction fragment, and its size was restored after phenotypic reversion. One ethyl methanesulfonate-induced allele had a deletion in the restriction fragment adjacent (distal) to the fragment altered in the insertional alleles. These two restriction fragments were immediately adjacent to the s38 chorion gene. Associated with the two altered restriction fragments were two RNA species, an abundant 3.2-kilobase (kb) poly(A)+ RNA and a minor 4.0-kb RNA. Several other less-abundant RNA species were detectable with more-sensitive single-stranded RNA probes. The otu gene was transcribed proximal to distal relative to the centromere; this was opposite to the direction of transcription of the adjacent s38 gene. During development, the 3.2-kb RNA was absent in larvae, first appeared in the pupal stages, and persisted in adult females, in which it was most prevalent in the ovaries. The DNA that hybridized to the 3.2-kb ovarian RNA hybridized to four different RNAs found in the testes but not in the rest of the adult male. These testis-enriched RNAs were transcribed from the same strand of DNA as the ovarian transcripts.Our understanding of germ cell determination and differentiation in Drosophila melanogaster oogenesis is derived largely from morphological and genetic studies. During oogenesis, a single apical ovarian cell, the germarial cystoblast, undergoes four incomplete cell divisions to produce a syncytium of 16 interconnected cystocytes. One of these cystocytes differentiates into an oocyte (19), while the remaining 15 become the nurse cells that nourish the growing oocyte via intercellular cytoplasmic bridges (8,(26)(27)(28) and provide it with RNAs and proteins that will be required during early embryogenesis (30).Of central interest in germ cell development is the mechanism by which 1 cystocyte develops into an oocyte and the other 15 cystocytes develop into nurse cells. Within a 16-cell syncytium, the number of intercellular bridges varies from one to four per cell, with only 2 of the 16 cystocytes having four bridges. Immediately after the formation of the 16-cell cluster, both four-canal cells enter meiotic prophase (27, 28). However, one of these cells subsequently enters the nurse cell developmental pathway, while the other develops as an oocyte. It therefore appears that four cytoplasmic bridges are a necessary but not sufficient prerequisite for determination of oocyte development.We are interested in the early events of oogenesis and specifically in genes that regulate the morphogenesis of the germ cells themselves. The otu gene is one of several genes whose products are required for the determination and differentiation of oocytes and nur...