Suppression of a lethal trisomic phenotype in Drosophila melanogaster by increased dosage of an unlinked locus

A family of genes clustered at the Triplo-lethal locus of Drosophila melanogaster has an unusual evolutionary history and significant synteny with Anopheles gambiae

Within the unique Triplo-lethal region (Tpl) of the Drosophila melanogaster genome we have found a cluster of 20 genes encoding a novel family of proteins. This family is also present in the Anopheles gambiae genome and displays remarkable synteny and sequence conservation with the Drosophila cluster. The family is also present in the sequenced genome of D. pseudoobscura, and homologs have been found in Aedes aegypti mosquitoes and in four other insect orders, but it is not present in the sequenced genome of any noninsect species. Phylogenetic analysis suggests that the cluster evolved prior to the divergence of Drosophila and Anopheles (250 MYA) and has been highly conserved since. The ratio of synonymous to nonsynonymous substitutions and the high codon bias suggest that there has been selection on this family both for expression level and function. We hypothesize that this gene family is Tpl, name it the Osiris family, and consider possible functions. We also predict that this family of proteins, due to the unique dosage sensitivity and the lack of homologs in noninsect species, would be a good target for genetic engineering or novel insecticides.

The haplolethal region at the 16F gene cluster of Drosophila melanogaster: structure and function

Extensive aneuploid analyses had shown the existence of a few haplolethal (HL) regions and one triplolethal region in the genome of Drosophila melanogaster. Since then, only two haplolethals, 22F1-2 and 16F, have been directly linked to identified genes, dpp and wupA, respectively. However, with the possible exception of dpp, the actual bases for this dosage sensitivity remain unknown. We have generated and characterized dominant-lethal mutations and chromosomal rearrangements in 16F and studied them in relation to the genes in the region. This region extends along 100 kb and includes at least 14 genes. The normal HL function depends on the integrity of a critical 4-kb window of mostly noncoding sequences within the wupA transcription unit that encodes the muscle protein troponin I (TNI). All dominant lethals are breakpoints within that window, which prevent the functional expression of TNI and other adjacent genes in the proximal direction. However, independent mutations in these genes result in recessive lethal phenotypes only. We propose that the HL at 16F represents a long-range cis regulatory region that acts upon a number of functionally related genes whose combined haploidy would yield the dominant-lethal effect.

A genetic screen of the Drosophila X chromosome for mutations that modify Deformed function

We have screened the Drosophila X chromosome for genes whose dosage affects the function of the homeotic gene Deformed. One of these genes, extradenticle, encodes a homeodomain transcription factor that heterodimerizes with Deformed and other homeotic Hox proteins. Mutations in the nejire gene, which encodes a transcriptional adaptor protein belonging to the CBP/p300 family, also interact with Deformed. The other previously characterized gene identified as a Deformed interactor is Notch, which encodes a transmembrane receptor. These three genes underscore the importance of transcriptional regulation and cell-cell signaling in Hox function. Four novel genes were also identified in the screen. One of these, rancor, is required for appropriate embryonic expression of Deformed and another homeotic gene, labial. Both Notch and nejire affect the function of another Hox gene, Ultrabithorax, indicating they may be required for homeotic activity in general.