Molecular analysis of a candidate gene for the reproductive isolation between sibling species ofDrosophila

Abstract

The X-linked gene Hmr in Drosophila melanogaster, when mutated, rescues otherwise inviable interspecific hybrids from crosses between D. melanogaster and any of its three most closely related species D. simulans, D. mauritiana and D. sechellia. DNA from the site of a breakpoint at the putative locus of the gene has been cloned, and results of transcription and sequence analyses are presented. Three distinct mRNAs are transcribed from this locus, two of which are abundantly expressed throughout life. A third transcript, which is larger but rarer, appears to be disrupted by at least one of the two known mutations of Hmr. The gene encodes a mitochondrial ADP/ATP translocator protein, which plays an essential role in maintaining metabolic energy. Analysis of several cDNAs suggested that the rescue of hybrids may be dependent on mutations in the variable 3' end region of this gene, affecting the level and/or the stability of the largest messenger RNA.

Reduced Fertility of Drosophila melanogaster Hybrid male rescue (Hmr) Mutant Females Is Partially Complemented by Hmr Orthologs From Sibling Species

“…The distal breakpoint of the inversion at cytological position 9E7-8 is fairly close to the estimated cytological position of the Hmr 1 rescue allele at 9D1-9E4 (Hutter et al 1990). These findings raised the possibility that, allowing for some imprecision in the genetic mapping and cytological analyses, the breakpoint of In(1)AB was disrupting the same gene responsible for rescue in Hmr 1 (Hutter and Karch 1994). Subsequent analysis, however, refuted this possibility by showing that the gene broken by the In(1)AB distal breakpoint, sesB, has no role in hybrid lethality (Zhang et al 1999).…”

X-linked small GTPase and OXPHOS genes are candidates for the genetic basis of hybrid inviability in Drosophila

“…In previous work my colleagues and I showed that two of the above D. melanogaster mutants, Hmr and In(1)AB, which rescue otherwise lethal hybrids between this species and its closest relatives, mapped meiotically to cytological interval 9D/E on the X polytene chromosome (Hutter and Ashburner 1987;Hutter et al 1990; Barbash et al 2000). By performing in situ hybridization to polytene chromosomes, Hutter and Karch (1994) observed a DNA sequence that is repeated four times, both in mutants and wild-type flies, within the above 9D/E genomic DNA interval, though the repeat sequence was not found elsewhere in the genome. Here I show that this repeat lies 440 base pairs (bp) 3' of the CG1619 gene, and shares strong homology with genes encoding small Rab GTPase proteins.…”

“…Small GTPases were first found to be involved in the control of vesicular transport between the endoplasmic reticulum (ER) and the Golgi apparatus (Mattaj and Englmeier 1998). In addition to the possible implication of small GTPases in Drosophila hybrid inviability, Hutter and Karch (1994) and results from the present study show that both Hmr and In(1)AB mutants (i.e. two out of the three hybrid rescue mutants identified so far in D. melanogaster) harbor a major germline lesion very near or within an untranslated region (UTR) of two genes closely linked to the above small GTPase genes in 9D/E, and involved in the oxidative phosphorylation (OXPHOS) process.…”

Cytogenetic mapping of the Lethal hybrid rescue gene of Drosophila simulans.

“…So far four genes have been reported as hybrid rescue genes, which are Lethal hybrid rescue (Lhr) and maternal hybrid rescue (mhr) of D. simulans, and Hybrid male rescue (Hmr) and zygotic hybrid rescue (zhr) of D. melanogaster (Watanabe, 1979;Hutter and Ashburner 1987;Hutter et al, 1990;Sawamura et al, 1993aSawamura et al, , 1993bSawamura et al, , 1993c In order to understand the genetic mechanisms by molecular terms, it is the basic requirement to map the gene location on the chromosomes. In D. simulans, however, available visible marker genes and chromosome rearrangements are so few that genetic analyses as extensive as in D. melanogaster are impossible to be done.…”