Gene regulation in Drosophila mulleri, D. arizonensis , and their hybrids: The nucleolar organizer

Abstract

Typically, Dwsophila have nucleolar organizer regions (NORs) confined to the sex chromosomes. Salivary gland cells of hybrids between Drosophila mulleri females and D. arizonensis males exhibit features in nucleolar organizer regulation that differentiate the species on one hand, and which show an interplay between the X and the microchromosome on the other hand.

C-banding in the polytene chromosomes of species of the plumosus group (Diptera, Chironomidae) and their experimental hybrids

“…Such a change is well developed in inter-species hybrids: C. plumosus x C. vancouveri and C. plumosus x C. balatonicus. We suppose that the mechanisms acting in hybrids of D. mafleri × D. arizonensis (Bicudo & Richardson, 1977) are in effect here as well. In the initial form ofD.…”

The chromosomes of two Drosophila races: D. nasuta nasuta and D. nasuta albomicans III. Localization of nucleolar organizer regions

“…Such a distribution of the NORs has not yet been reported in Drosophila. In other Drosophila species, where the NORs have been localized, they are restricted either to the X and Y chromosomes ( D. melanogaster, D. simulans, D. hyde# Spear, 1974;Hennig et al, 1975;Mohan, 1977), to the X chromosomes (D. virilis, D. mulleri, D. arizonensis, " Endow & Gall, 1975;Bicudo & Richardson, 1977) or to the microchromosomes only (D. tumiditarsus, " Sinibaldi & Cummings, 1981). Our findings in the two Drosophila nasuta races are the second cases where the X chromosomes are devoid of NORs.…”

EVOLUTION IN HAWAIIAN DROSOPHILIDAE. III. THE MICROCHROMOSOME AND HETEROCHROMATIN OF DROSOPHILA

“…In related studies they suggested that the regulation of the nucleolar organizer region could be related to interspecific differences in developmental rates and, possibly, to hybrid inviability (Bicudo and Richardson, 1978) . Since developmental rates, mating behavior and viability all may be affected by a single change in the location of a block of heterochromatin, repositioning heterochromatin in the genome may have far greater effect on the phenotypic diversity of organisms than would, say, a mutation in a structural gene.…”

“…Recently, Bicudo and Richardson (1977) have reported interchromosomal effects on gene regulation (nucleolar organizer activity) between the microchromosomes and the X, which extends the realm of the potential effects on genetic regulation to a higher order effect, beyond the single chromosome. In related studies they suggested that the regulation of the nucleolar organizer region could be related to interspecific differences in developmental rates and, possibly, to hybrid inviability (Bicudo and Richardson, 1978) .…”

“…The X and microchromosome may be of common phylogenetic origin (Stone and Griffen, 1940;Sandler and Novitski, 1956), and over several species these three chromosomes exhibit the following relict features: they are frequently involved in ectopic pairing (Kaufmann and Gay, 1969) and reciprocal translocations (Sandler and Novitski, 1956); they show a variety of genetic regulatory interactions, including loci which may be combined to exhibit cis-dominant variegation effects (Judd, 1955) and position effects on puffing (Kaufmann and Gay, 1969); they exhibit interchromosomal suppressor effects of lethals (Parker, 1954); and they exhibit both dominant and epistatic interactions affecting nucleolar organizer region activity (Bicudo and Richardson, 1977). In D. busckii the microchromosome and the X chromosome are joined, as demonstrated by X-linked mutants in D. busckii which are apparently homologous to microchromosome linked mutants of D. melanogaster (Krivshenko, 1959;Hochman, 1976) .…”