Showing papers on "Dosage compensation published in 1981"

The link between dosage compensation and sex differentiation in Drosophila melanogaster.

Abstract: The rate of 3H-uridine incorporation into X-chromosome and autosomal RNA was measured as an indicator of relative transcription activity in larvae carrying various Sxl mutant alleles. Hyperactivity of X chromosomes was found in heteroallelic Sxlf#1/Sxlfhv#1 and homozygous Sxlf#2 female larvae. Sxlfhv#1 homozygotes, Sxlf#1/Sxl+ heterozygotes, heteroallelic Sxlf#2/Sxlf#2 as well as homozygous Sxlf#ba female larvae exhibited normal X chromosome transcription. Except for Sxlf#ba, there is a correlation between the viability of the mutants and the degree to which X-chromosome activity is elevated. Male larvae carrying the dominant male-specific lethal mutation SxlM#1 displayed X chromosomes only half as wide as those of control larvae. However, it could not be determined whether this property is the result of a lower transcription rate or of underreplication of the mutated X chromosomes. The results demonstrate that the Sxl gene plays an important role in controlling X-chromosome activity. The relationship among the various genes known to act in sex differentiation and dosage compensation is discussed.

Chromosome banding in Amphibia. VI. BrdU-replication patterns in anura and demonstration of XX/XY sex chromosomes in Rana esculenta.

Abstract: A modified BrdU-Hoechst-Giemsa technique permitted the demonstration of easily reproducible replication patterns in the somatic chromosomes of Amphibia. These banding patterns allow for the first time a precise identification of all chromosomes and the analysis of the patterns of replication in the various stages of S-phase in Amphibia. Several possibilities for the use of this technique were demonstrated on three frog species of the family Ranidae, all differing greatly in their DNA-content. With this method, the homomorphic chromosome pair No. 4 in Rana esculenta could be identified as sex-specific chromosomes of the XX/XY-type. All male animals exhibit an extremely late replicating region in the Y-chromosome, which is lacking in the X-chromosome in the female animals, both X-chromosomes replicate synchronously. These sex-specific chromosomes cannot be distinguished by other banding techniques. In the highly heteromorphic ZZ/ZW-sex chromosome system of Pyxicephalus adspersus a synchronous replication of the two Z-chromosomes of male animals and a very late replication of the short arm of the W-chromosomes of male animals was demonstrated. These results support the assumption that there is no dosage compensation for Z-linked or X-linked genes by the sex chromosome inactivation mechanism in the sex chromosomes of Amphibia.

The Genetic Basis of Dosage Compensation of Alcohol Dehydrogenase-1 in Maize

Abstract: The levels of alcohol dehydrogenase (ADH) do not exhibit a structural gene-dosage effect in a one to four dosage series of the long arm of chromosome one (1L) (Birchler 1979). This phenomenon, termed dosage compensation, has been studied in more detail. Experiments are described in which individuals aneuploid for shorter segments were examined for the level of ADH in order to characterize the genetic nature of the compensation. The relative ADH expression in segmental trisomics and tetrasomics of region 1L 0.72-0.90, which includes the Adh locus, approaches the level expected from a strict gene dosage effect. Region 1L 0.20-0.72 produces a negative effect upon ADH in a similar manner to that observed with other enzyme levels when 1L as a whole is varied (Birchler 1979). These and other comparisons have led to the concept that the compensation of ADH results from the cancellation of the structural gene effect by the negative aneuploid effect. The example of ADH is discussed as a model for certain other cases of dosage compensation in higher eukaryotes.

Genetic analysis of the larval secretion gene Sgs-4 and its regulatory chromosome sites in Drosophila melanogaster.

Abstract: Larval salivary gland secretion from seven wild-type stocks of Drosophila melanogaster was electrophoretically analyzed. Considerable variability occurs in the X-chromosomally coded secretion protein 4, both qualitatively, as expressed by differences in electrophoretic mobilities, and quantitatively as seen by its relative amount in the secretion. Drosophila stocks with “normal” amounts of protein 4 show approximately 80–90% dosage compensation in the males, whereas in two stocks with lower amounts of protein 4 there is no indication of dosage compensation. — Genetic analysis showed that the properties of secretion protein 4 and the level of expression of the Sgs-4 gene are controlled by the X-chromosome. Recombination experiments indicate that the stock-specific characteristics of protein 4 are properties of the structural gene Sgs-4 itself or of a chromosome region immediately adjacent to Sgs-4. One recombinant (R + 79), manifesting an intermediate level of dosage compensation, indicates that a chromosome segment closely distal to Sg-4 is responsible for the regulation of the gene and for dosage compensation in particular. Accordingly, Sgs-4 must be transcribed from distal to proximal. Its position on the genetic map is 3.6. Two stocks, Hikone-R and Kochi-R, which were originally described as 0-mutants produce very low amounts of a specific secretion protein, 4 h, as revealed by a transvection effect and also by fluorography of overloaded gels.

Chromosomal basis of dosage compensation in Drosophila. X. Assessment of hyperactivity of the male X in situ.

Abstract: The results of examination of the template activity of the fixed polytene chromosomes of Drosophila hydei, monitored by 3H-UTP, under in situ assay conditions, upon the use of endogenous Drosophila polymerase, exogenous Escherichia coli RNA polymerase (holoenzyme) and exogenous Drosophila RNA polymerase II (or B) have been presented. Analysis of the data reveals that the transcription patterns with the 3 enzymes are not strictly comparable with the pattern obtained under in vivo conditions. Yet, with each of the 3 conditions of assay, there is a reasonable concordance between the template activity on the single X chromosome of the male and the paired Xs of the female, as observed under in vivo. There is also, in every case, a high positive correlation between the 3H-UMP incorporation into the X chromosome and that into a specific autosome. A site-wise analysis of 3H-UMP labelling under the 3 assay conditions also reveals that for most of the regions, the sites which are highly active in vivo also show high labelling in situ, and the proportionally is maintained in both sexes. These result have been interpreted to have suggested that the hyperactivity of the male X vis-a-vis dosage compensation in Drosophila is primarily a property of the inherent organization of the X chromosome itself and is achieved through modulation in the organization, rather than exclusively through autosomal factor(s), although a secondary level of autosomal regulation has not yet been ruled out.

Transcription in X-chromosomal segmental aneuploids of Drosophila melanogaster and regulation of dosage compensation

Abstract: Transcription of X chromosomal DNA has been examined autoradio-graphically in various 1X2A and 2X2A normal larvae and 1X2A (+ X fr) and 2X2A (+ X fr) segmental aneuploid larvae of species Drosophila melanogaster. The segmental aneuploids contained duplications for the segment 9A–11A and 15D–ISA of the X chromosome. Results show that in the aneuploid male containing 9A–11A duplicaton both the homologous segments involved in the aneuploidy are autonomously hyperactive; their combined activity, measured by X/A grain ratio, is found to be nearly 70% more than the activity in normal male and about 100% more than that in diplo-X female. In the aneuploid female, containing the aneuploid segment 15D–18A and having three doses of the segment of the X chromosome, the activity was over 100% more than the diplo-X activity. The per gene dose activity for the two segments in the aneuploid male and female, respectively, is also significantly higher than their male and female counterparts. The possible role of lack of contiguity of the genetic segments and an intra-nuclear variation has been ruled out by appropriate analysis. We, therefore, interpret these findings to be due to an autonomous expression of the X linked compensatory genes, resulting from a primary modulation in the organization of the entire X chromosome. The autosomal signal then renders the individual genetic locus hyperactive.

Dosage compensation of x-chromosome activity in interspecific hybrids of Drosophila melanogaster and D. simulans.

Abstract: We have used the unstable ring X-chromosome of D. melanogaster to generate XX/X0 mosaics in the hybrid progeny from crosses between D. melanogaster females and D. simulans males. The functional properties of the polytene X-chromosome(s) in salivary glands of such X0/XX mosaic hybrid larvae have been analysed by autoradiography after 3H-uridine or 3H-thymidine labelling of the glands. The simulans X-chromosome in the hybrid X0 nuclei displays typical pale staining, enlarged diameter, higher rate of transcription (nearly two times higher than each of the Xs in the XX nuclei in the same gland) and a faster completion of replication as would be the case in the original parental X0 or XY nuclei. In the hybrid XX polytene nuclei, the melanogaster as well as the simulans X functions in the same manner as in female cells of the parents. The nucleolar transcription is also equal in the hybrid XX and X0 nuclei. Thus is seems that despite the evolutionary diversification between these two species, the regulator system which brings about the dosage compensation of X-chromosome activity has been conserved.

Measurement of the ratio of the number of X chromosomes to sets of autosomes in Drosophila melanogaster

Abstract: In Drosophila melanogaster both sex determination and dosage compensation are governed by the ratio of the number of X chromosomes to sets of autosomes. We propose a mechanism by which this ratio can be measured at the cellular level. The mechanism helps in understanding the effects of, and interactions among, mutants affecting the processes of sex determination and dosage compensation.