Biomedical subjects

H Hollocher

Publications and source records attributed to H Hollocher.

22 records · Page 2Linked to original sources

PubMed1992

The molecular through ecological genetics of abnormal abdomen. IV. Components of genetic variation in a natural population of Drosophila mercatorum.

Natural populations of Drosophila mercatorum are polymorphic for a phenotypic syndrome known as abnormal abdomen (aa). This syndrome is characterized by a slow-down in egg-to-adult developmental time, retention of juvenile abdominal cuticle in the adult, increased early female fecundity, and decreased adult longevity. Previous studies revealed that the expression of this syndrome in females is controlled by two closely linked X chromosomal elements: the occurrence of an R1 insert in a third or more of the X-linked 28S ribosomal genes (rDNA), and the failure of replicative selection favoring uninserted 28S genes in larval polytene tissues. The expression of this syndrome in males in a laboratory stock was associated with the deletion of the rDNA normally found on the Y chromosome. In this paper we quantify the levels of genetic variation for these three components in a natural population of Drosophila mercatorum found near Kamuela, Hawaii. Extensive variation is found in the natural population for both of the X-linked components. Moreover, there is a significant association between variation in the proportion of R1 inserted 28S genes with allelic variation at the underreplication (ur) locus such that both of the necessary components for aa expression in females tend to cosegregate in the natural population. Accordingly, these two closely linked X chromosomal elements are behaving as a supergene in the natural population. Because of this association, we do not believe the R1 insert to be actively transposing to an appreciable extent. The Y chromosomes extracted from nature are also polymorphic, with 16% of the Ys lacking the Y-specific rDNA marker. The absence of this marker is significantly associated with the expression of aa in males. Hence, all three of the major genetic determinants of the abnormal abdomen syndrome are polymorphic in this natural population.

Abdomen↗

PubMed1989

Natural selection and ribosomal DNA in Drosophila.

Natural populations of Drosophila mercatorum are variable for the number of X-linked 28S ribosomal genes bearing a 5-kilobase insert. A separate polymorphic X-linked gene controls whether 28S repeats bearing the insert are preferentially underreplicated during the formation of polytene tissue. Female flies having at least a third of their 28S genes bearing the insert and lacking the ability to preferentially underreplicate inserted repeats display the abnormal abdomen syndrome. The syndrome is characterized by retention of juvenile abdominal cuticle into the adult, a slowdown in larval developmental time, and an increase in early female fecundity. The life history traits are expressed in nature and provide a basis for strong natural selection. The abnormal abdomen syndrome should be favored whenever the adult age structure is skewed towards young individuals, and field studies confirm this prediction. The closely related species, Drosophila hydei, also bears these inserts and appears to be subject to similar selection. However, D. mercatorum responds to this selection primarily through the allelic variation that controls preferential underreplication, whereas D. hydei responds primarily through adjustment of the proportion of inserted 28S genes. This is interpreted to mean that the evolution of a multigene family arises from the interaction of population-level and DNA-level processes.

Animals↗

PubMed1987

Reexamination of alcohol dehydrogenase structural mutants in Drosophila using protein blotting.

Using protein blotting and an immuno-overlay procedure, we have reexamined the cross-reacting material produced by ADH null-activity mutants generated with ethyl methanesulfonate (EMS). Of the 13 mutants, 11 have an immunodetectable polypeptide of wild-type size. The native and urea denatured isoelectric points (pI) establish that 7 of 13 of the mutations have no effect on protein charge. The electrophoretic mobilities of each variant on increasing percent acrylamide gels (Ferguson analysis), reveal that 9 of the 11 immunodetectable mutants have retained the ability to form dimers under native conditions. None of the inactive mutant proteins has the ability to form the "adduct-bound" isozyme. We have found no correlation between protein pI and in vivo stability. The observed frequencies of specific charge class alterations do not dispute the propensity of G:A transitions previously found for EMS mutagenesis.

Alcohol Dehydrogenase↗

PubMed1987

Partial correction of structural defects in alcohol dehydrogenase through interallelic complementation in Drosophila melanogaster.

Alcohol dehydrogenases (ADH) from the F1 progeny of all pairwise crosses between 12 null-activity mutants and crosses between these mutants and four active variants, ADHn5 ADHF, ADHD and ADHS, were analyzed for the presence of active or inactive heterodimers. Gels were stained for ADH enzyme activity, and protein blots of duplicate gels were probed with ADH-specific antibody to detect cross-reacting material. Crosses between the three major electrophoretic variants. ADHF, ADHS and ADHD, all produced active heterodimers. Four mutant proteins (ADHn2, ADHn4, ADHn10 and ADHn13) did not form heterodimers with any other ADH subunit tested. Of the 28 crosses involving the remaining null activity mutants, 22 produce heterodimers. Twelve of these exhibit partial restoration of enzyme activity. In five cases of active heterodimers from null-activity crosses, Adhn11 supplied one of the subunits. In two crosses involving the active variant ADHD, the null activity mutant subunits (ADHn8 and ADHn3) destabilized the heterodimer sufficiently to cause inactivation of the ADHD subunit. In the cross between AdhF and Adhn3, the activity of the ADHF subunit was also greatly reduced in association with the ADHn3 subunit. Two crosses (Adhn1 X Adhn11 and Adhn5 X Adhn12) result in partial restoration of one of the homodimeric proteins (ADHn1 and ADHn12, respectively), as well as forming active heterodimers.

Alcohol Dehydrogenase↗