Effect of temperature on interaction of Abruptex and recessive alleles of the Notch complex locus of Drosophila melanogaster

Abstract

Interaction of recessive visible alleles ( / u g , ,fa"", spl, nd, nd2) and different Abruptex ( A x ) alleles of the Notch locus of Drosophila melanogaster was analysed at 18°C. 2 5°C and 29°C in transheterozygotes. The homozygous viable Ahruptex alleles complement most of the recessives at all temperatures. The expression of hypomorphic Ahruptex alleles (AXE', Ax1b172, Ax71d) remains constant at all temperatures, whereas the expression of hypermorphic alleles (AxZs, AxyBz) is not only complement all of the recessives at 1 8 T , hut their own phenotypic expression is usually very strong. At 25°C they fail to complement spl andfag, and their own phenotypic expression is reduced. At 29°C the lethal Abruptex alleles do not complement any of the recessives except nd, and their own expression is reduced or almost absent. At low temperatures the lethal Ahruptex alleles compete efficiently with the wild-type allele, hut at elevated temperatures their competetive ability is decreased. The results strongly support the view that the Notch complex gene is a single cistron, hut that the Ahruptex site may possibly have three functionally different mutant forms: hypomorphic, hypermorphic, and antimorphic. The morphism may, however, he different in different functions of the gene which may suggest independence of the pleiotropic effects of the gene.

Cis-trans tests at the Notch locus of Drosophila melanogaster suggesting multiple cis-acting control sites inside the locus

“…If our hypothesis of multiple cis-acting control sites in the Notch locus is correct, the Notch locus is similar to the rosy locus for example. However, in the case of rosy, the control sites map outside of the cistron of xanthine dehydrogenase, whereas in the case of Notch the presumed control sites map within a region which appears genetically to be a single cistron (WELSHONS and VON HALLE 1962;WELSHONS 1965;SHELLENBARGER and MOHLER 1975;PORTIN 1977). This property of the Notch locus does not, however, contradict the hypothesis of the division of the locus into regulatory and structural parts.…”

The antimorphic mode of action of lethal Abruptex alleles of the Notch locus in Drosophila melanogaster

“…They do not complement the Notch lethal mutations. At 25°C the lethal Abruptex mutations also complement the visible recessive alleles (except f&) of the Notch locus (PORTIN 1977). The lethal Abruptex alleles also have a completely different phenotype in heterozygous condition than the Notch mutations.…”