The Homologous Drosophila Transcriptional Adaptors ADA2a and ADA2b Are both Required for Normal Development but Have Different Functions

ABSTRACT In Drosophila and several other metazoan organisms, there are two genes that encode related but distinct homologs of ADA2-type transcriptional adaptors. Here we describe mutations of the two Ada2 genes of Drosophila melanogaster. By using mutant Drosophila lines, which allow the functional study of individual ADA2s, we demonstrate that both Drosophila Ada2 genes are essential. Ada2a and Ada2b null homozygotes are late-larva and late-pupa lethal, respectively. Double mutants have a phenotype identical to that of the Ada2a mutant. The overproduction of ADA2a protein from transgenes cannot rescue the defects resulting from the loss of Ada2b, nor does complementation work vice versa, indicating that the two Ada2 genes of Drosophila have different functions. An analysis of germ line mosaics generated by pole-cell transplantation revealed that the Ada2a function (similar to that reported for Ada2b) is required in the female germ line. A loss of the function of either of the Ada2 genes interferes with cell proliferation. Interestingly, the Ada2b null mutation reduces histone H3 K14 and H3 K9 acetylation and changes TAF10 localization, while the Ada2a null mutation does not. Moreover, the two ADA2s are differently required for the expression of the rosy gene, involved in eye pigment production, and for Dmp53-mediated apoptosis. The data presented here demonstrate that the two genes encoding homologous transcriptional adaptor ADA2 proteins in Drosophila are both essential but are functionally distinct.

An attempt to hybridize Drosophila species using pole cell transplantation.

We have made hybrid embryos in Drosophila by pole cell transplants, by transferring pole cells from two species, D. rajasekari and D. eugracilis, into sterile D. melanogaster hosts. These females were then mated to melanogaster males and the older these females were, the further their hybrid offspring developed. In the case of the rajasekari/melanogaster hybrids, the embryos form cuticle but had defective heads, while the eugracilis/melanogaster hatched as larvae that grew but did not moult to the second instar. Hybrid pole cells could be transferred to melanogaster hosts but they failed to make eggs.

Sex determination in the germ line of Drosophila melanogaster: activation of the gene Sex-lethal

The germ line exhibits sexual dimorphism as do the somatic tissues. Cells with the 2X;2A chromosome constitution will follow the oogenic pathway and X;2A cells will develop into sperm. In both somatic and germ-line tissues, the sexual pathway chosen by the cells depends on the gene Sex-lethal (Sxl), whose function is continuously needed for female development. In the soma, the sex of the cells is autonomously determined by the X:A signal while, in the germ line, the sex is determined by cell autonomous (the X:A signal) and somatic inductive signals. Three X-linked genes have been identified, scute (sc), sisterless-a (sis-a) and runt (run), that determine the initial functional state of Sxl in the soma. Using pole cell transplantation, we have tested whether these genes are also needed to activate Sxl in the germ line. We found that germ cells simultaneously heterozygous for sc, sis-a, run and a deficiency for Sxl transplanted into wild-type female hosts develop into functional oocytes. We conclude that the genes sc, sis-a and run needed to activate Sxl in the soma seem not to be required to activate this gene in the germ line; therefore, the X:A signal would be made up by different genes in somatic and germ-line tissues. The Sxlf7M1/Sxlfc females do not have developed ovaries. We have shown that germ cells of this genotype transplanted into wild-type female hosts produce functional oocytes. We conclude that the somatic component of the gonads in Sxlf7M1/Sxlfc females is affected, and consequently germ cells do not develop.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex determination in germ line chimeras of Drosophila melanogaster

Of 55 flies developing from blastoderms which had received male or female pole cell transplants, 15 (7 females and 8 males) were shown by progeny testing to be germ line chimeras. Since donor and host pole cells were genetically marked with contrasting X- or Y-linked alleles, the progeny testing scheme enabled the genotypic sex of the donor component undergoing gametogenesis to be identified as either the same as (‘homosexual’ chimeras) or opposite (‘heterosexual’ chimeras) that of the host. All seven of the female chimeras were identified as ‘homosexual’ chimeras carrying only chromosomally female donor and XX host germ cells. Similarly, all eight males were shown to be ‘homosexual’ chimeras with chromosomally male XY donor and XY host germ cells. The chromosomal sex of the donor component undergoing gametogenesis was in every case the same as the phenotypic sex of the host. Since there is an equal probability of constructing either a ‘homosexual’ or a ‘heterosexual’ chimera during pole cell transplantation, the ability of pole cells to differentiate functional gametes in hosts of the opposite sex was tested 50 % of the time even if sex reversal of these donor pole cells could not be demonstrated. Thus the absence of ‘heterosexual’ chimerism strongly supports the interpretation that the phenotypic sex of a germ cell in Drosophila is determined entirely by its own chromosome constitution, not by that of the gonadal mesoderm.