In the Bar mutation of Drosophila, ommatidial differentiation is known to be suppressed in the anterior portion of the eye. Our structural analysis shows that the Bar region contains a pair of homeo box genes, BarHl and BarHZ. These genes encode polypeptides similar in size and sequence and share a common homeo domain that is identical in sequence except for putative trflns-activator-binding sites. We also show, by mosaic analysis and immunostaining with anti-BarHl/BarH2 antibodies, that BarHl and BarHZ are not only specifically coexpressed but also functionally required in R1/R6 prephotoreceptors and primary pigment cells in developing ommatidia. In R1/R6, the expression of BarHl and BarHZ appears to be regulated by rough and glass gene products. BarHl and BarHZ proteins are essential to normal lens formation, formation of three types of pigment cells, and elimination of excess cells from mature ommatidia. Taken together, our results suggest that Bar homeo domain proteins may play key roles in the fate-determination processes of pigment cells and cone cells.
The Bar mutation B of Drosophila melanogaster and optic morphology mutation Om(JD) of Drosophila ananassae result in suppression of ommatidium differentiation at the anterior portion of the eye. Examination was made to determine the genes responsible for these mutations. Both loci were found to share in common a different type of homeobox gene, which we call "BarH1." Polypeptides encoded by D. melanogaster and D. ananassae BarHl genes consist of 543 and 604 amino acids, respectively, with homeodomains identical in sequence except for one amino acid substitution. A unique feature of these homeodomains is that the phenylalanine residue in helix 3, conserved in all metazoan homeodomains so far examined, is replaced by a tyrosine residue. By Northern blotting, considerably more BarH1 RNA was detected in the Bar mutant than in wild type. P element-mediated transformation showed Bar-like eye malformation to be induced by transient overexpression of the BarH1 gene in the late thirdinstar larvae. Somatic recombination analysis indicated normal gene functions ofthe Bar region, including the BarH1 gene, to be required for normal eye morphogenesis.
Mutations in the forked (f) gene of Drosophila cause deformation of bristles and hairs. Our molecular analysis showed the f gene to span more than 30 kb, and to encode two major RNAs, 6.0 and 2.5 kb long, both of which are prematurely terminated in gypsy and springer insertion mutants. These truncated RNAs were polyadenylated using putative polyadenylation signals within the 5'-LTR of the inserted retrotransposon. No evidence was found for effects of the retrotransposon insertions on the promoters for transcription of the 6.0 and 2.5 kb RNAs. In f1 and fx, a single gypsy element was found to be inserted at identical sites in the second intron of region encoding the 2.5 kb f RNA and both truncated and wild-type sized RNAs were detected. Recessive mutations at suppressor of forked (su(f)) increased the fraction of wild-type sized RNAs considerably, suggesting that the wild-type su(f) product either stimulates premature termination at the gypsy LTR or inhibits normal splicing. In f36a, a springer element inserted in the third exon of the region encoding the 2.5 kb f RNA completely suppressed the formation of apparently wild-type transcripts.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.