Cytogenetical localization of Zygotic hybrid rescue (Zhr), a Drosophila melanogaster gene that rescues interspecific hybrids from embryonic lethality

Abstract

Hybrid females from crosses between Drsophila melanogaster males and females of its sibling species, D. simulans, D. mauritiana, or D. sechellia die as embryos. This lethality is believed to be caused by incompatibility between the X chromosome of D. melanogaster and the maternal cytoplasm. Zygotic hybrid rescue (Zhr) prevents this embryonic lethality and has been cytogenetically mapped to a proximal region of the X chromosome of D. melanogaster, probably in the centromeric heterochromatin. We have carried out high resolution cytological mapping of Zhr using deficiencies and duplications of the X heterochromatin. Deletions of the Zhr+ gene from the hybrid genome exhibit the Zhr phenotype. On the contrary, addition of the wild-type gene to the hybrid genome causes embryonic lethality, regardless of sex. The Zhr locus has been narrowed down to the region covered by Dp(1;f)1162 but not covered Dp(1;f)1205, a chromosome carrying a duplication of heterochromatin located slightly distal to the In(1)sc8 heterochromatic break-point.

Characterization of a reproductive isolation gene, zygotic hybrid rescue, of Drosophila melanogaster by using minichromosomes

“…Although we concluded that the location of the zhr gene is between the breakpoints of Dp(1;f)1162 and Dp(1;f)1205, the former, Dp(1;f)1162, itself had a partial effect on the lethality. A fraction of viables was consistently recovered in the hybrids carrying this minichromosome (Sawamura & Yamamoto, 1993;Sawamura et a!., 1995). This may mean that zhr gene activity is quantitative.…”

“…A minichromosome, Dp (1;f)1162, which was derived from the In (1)sc8 chromosome by an interstitial deletion, carries partial zhr gene activity (Sawamura & Yamamoto, 1993;Sawamura et a!., 1995). For further genetic characterization of the gene, flies carrying Dp(1;f)1162 were exposed to y-rays to produce new minichromosomes each of which had a deletion in the euchromatin-heterochromatin junction near which the zhr gene is located.…”

“…The zhr gene has been mapped in a heterochromatic region proximal to the In (1)sc'8 breakpoint but distal to the In(1)sc8 breakpoint (Sawamura & Yamamoto, 1993). Because Dp(1;f)1162 is a minichromosome derived frorr In(1)sc8 by a large interstitial deletion, it does not contain a heterochromatic portion distal to the zhr gene in the normal X chromosome order (Fig.…”

“…In our own studies, we have mapped a gene involved in the hybrid embryonic lethality, zhr, to a specific region of the X heterochromatin. We used minichromosomes which carry various amounts of X heterochromatin (Sawamura & Yamamoto, 1993). Although we concluded that the location of the zhr gene is between the breakpoints of Dp(1;f)1162 and Dp(1;f)1205, the former, Dp(1;f)1162, itself had a partial effect on the lethality.…”

Nup96-Dependent Hybrid Lethality Occurs in a Subset of Species From the simulans Clade of Drosophila

“…All four of these rescue strains increase the viability of F 1 hybrids. The D. melanogaster mutations Hybrid male rescue (Hmr) and Zygotic hybrid rescue (Zhr) appear to be loss-of-function mutations (Sawamura and Yamamoto 1993;Barbash et al 2000), while duplications of Hmr 1 and Zhr 1 reduce hybrid viability (Sawamura and Yamamoto 1993;Barbash et al 2000;Orr and Irving 2000). These observations suggest that the wild-type Hmr 1 and Zhr 1 genes cause hybrid lethality, but only Hmr has been molecularly cloned and shown to correspond to a single gene .…”