Polytene chromosomes show normal gene activity but some mRNAs are abnormally accumulated in the pseudonurse cell nuclei of Drosophila melanogaster otu mutants

Abstract

Certain mutant alleles of the ovarian tumor (otu) locus give rise to polytene chromosomes in the pseudonurse cells (PNCs). We have previously shown that the banding pattern of these germ line-derived chromosomes is similar to that in the larval salivary gland chromosomes. In this study, we have examined the gene activity of these chromosomes. General gene expression from these chromosomes was studied by uridine autoradiography. The expression of specific genes was monitored by in situ hybridisation to mRNA and also by combining enhancer trap lines with otu mutants. We found that most of the genes studied were expressed in the PNCs as they were in the wild-type nurse cells. Four out of the 12 mRNAs studied accumulated in the nuclei instead of migrating to the cytoplasm. The intensity of accumulation directly correlated with the extent of polytenisation in the PNC nuclei. We suggest that the otu mRNA remains partly attached to the polytene chromosome template after transcription and discuss the effects of this phenomenon on polytenisation of the PNC chromosomes.

Multiple Functions for Drosophila Mcm10 Suggested Through Analysis of Two Mcm10 Mutant Alleles

“…Similar defects in nurse cell nuclei decondensation have not been reported in DNA replication mutants but have been reported in numerous female-sterile mutations such as ovarian tumor (otu), string of pearls (sop), squid (sqd), tulipano (tlp), morula (mr), and rhino (rhi) (Cramton and Laski 1994;Heino et al 1995;Reed and Orr-Weaver 1997;Gigliotti et al 1998;Volpe et al 2001;Goodrich et al 2004). Rhino is of particular interest; it is a female-specific HP1-like chromodomain protein that has been postulated to modulate chromosome structure at the end of endo- cycle 5 (Volpe et al 2001).…”

Nurse cell polytene chromosomes ofDrosophila melanogaster otu mutants: Morphological changes accompanying interallelic complementation and position effect variegation

“…Heino et al [1995] have performed in situ hybridizations to identify mRNAs in the ovaries of otu 7 homozygotes. Messenger RNAs encoded by the genes ovo, otu, bcd, and pum were observed to be bound to localized regions of polytene chromosomes.…”

“…Since Drosophila nurse cells with polytene chromosomes can often function normally, we suggested that term ''pseudonurse'' be used only for those cells that resemble NCs but are not a part of a nurse cell/oocyte syncytium. Heino et al [1995] have performed in situ hybridizations to identify mRNAs in the ovaries of otu 7 homozygotes. Messenger RNAs encoded by the genes ovo, otu, bcd, and pum were observed to be bound to localized regions of polytene chromosomes.…”

“…Messenger RNAs encoded by the genes ovo, otu, bcd, and pum were observed to be bound to localized regions of polytene chromosomes. Although Heino et al [1995] call the cells with these giant chromosomes ''pseudonurse cells,'' the accompanying illustrations indicate that the cells with polytene chromosomes were in chambers containing oocytes. Whether or not a signal from the oocyte is necessary to start the NCs transcribing the mRNAs the oocyte will eventually receive remains to be determined.…”