Showing papers on "Dosage compensation published in 1974"
TL;DR: The differentiation of a particular X-chromosome as active or inactive is initiated in early embryogeny, and thereafter maintained through all further cell divisions in that individual, of great interest in relation to genetic control mechanisms in general.
Abstract: The X-chromosome of mammals is remarkable for its variable genetic activity. In somatic cells only a single X-chromosome is active, no matter how many are present, thus providing a dosage compensation mechanism by which males and females effectively have the same gene dosage of X-linked genes. In germ cells, however, it appears that all X-chromosomes present are active. Female germ cells require the presence of two X-chromosomes for normal survival, whereas male germ cells die if they have more than one X-chromosome. This system is found in all eutherian mammals and in marsupials, but is not known in any other animal group. In marsupials the X-chromosome derived from the father seems to be preferentially inactivated, whereas in eutherian mammals that from either parent may be so in different cells of the same animal. The differentiation of a particular X-chromosome as active or inactive is initiated in early embryogeny, and thereafter maintained through all further cell divisions in that individual. The mechanisms by which this is achieved are of great interest in relation to genetic control mechanisms in general. Various recent hypotheses concerning these mechanisms are discussed.
135 citations
TL;DR: It is indicated that a mechanism for dosage compensation is operative in both arms of the X chromosome of these two species.
Abstract: We have investigated the occurrence of dosage compensation in D. willistoni and D. pseudoobscura, two species whose X chromosome is metacentric with one arm homologous to the X and the other homologous to the left arm of chromosome 3 of D. melanogaster. Crude extracts were assayed for isocitrate dehydrogenase (XR), glucose-6-phosphate dehydrogenase (XL?), 6-phosphogluconate dehydrogenase (XL?), and alpha-glycerophosphate dehydrogenase (chromosome 2) in D. willistoni, and for esterase-5 (XR), glucose-6-phosphate dehydrogenase (XL?), 6-phosphogluconate dehydrogenase (XL?) and amylase (chromosome 3) in D. pseudoobscura. Our results indicate that a mechanism for dosage compensation is operative in both arms of the X chromosome of these two species.
31 citations
TL;DR: A working hypothesis is suggested according to which the X choromsome is inactivated during a critical stage of spermatogenesis in all male heterogametic organisms, as the inactivation is an essential control and not a compensatory step, leading to dominant male sterility.
Abstract: INACTIVATION of chromosomal elements is a process which takes place in various organisms, cell types, and cell cycle stages. The reasons for chromosome inactivation, which is superimposed on the more specific level of gene control, are different for the various systems. Dosage compensation in female mammals us. mitotic chromosome shut-off are the extreme cases. Since in many systems every chromosome may be in an active or inactive form, it is reasonable to assume, for the time being, that the molecular mechanism in different organisms is similar, thus justifying generalization. The role and behaviour of sex chromosomes during gametogenesis provide a striking example of differentiation of chromosomal elements and by inference reflect chromosome function. Precocious inactiviation of the X chromosome during seprmatogenesis together with activation of fertility factors on the Y in some organisms are of particular interest. In view of cytological and genetic observations we suggest a working hypothesis according to which the X choromsome is inactivated during a critical stage of spermatogenesis in all male heterogametic organisms. As the inactivation is an essential control and not a compensatory step, any interference with this process will change the developmental course of the spermatocyte leading to dominant male sterility (LIFSCHYTZ and LINDSEY 1972). In the course of this paper, the observations that support or lead to this view will be presented. Several experimental approaches we have undertaken to study further the genetics of the phenomenon, as well as its relation to Y chromsome activation, will be discussed.
30 citations
TL;DR: Comparison of transcription rates in X-chromosomes with the levels of two enzymes coded for by sex-linked genes in males, females, super-females and intersexes revealed that the dosage compensation of the enzyme synthesis is effected at the level of transcription.
Abstract: The intensity of transcription in the polytene X-chromosome of the salivary glands of Drosophila melanogaster has been determined as a function of the ratio of X-chromosomes to autosomes (X:A). Autoradiographic measurements revealed that the single X-chromosome in males (1X2A) incorporates twice as much label as each of the two X-chromosomes in females (2X2A) which confirms the earlier report of Mukherjee and Beermann (1965). The addition of the third autosome set in super-males (1X3A) does not result in an increase of RNA synthesis in the X-chromosomes as compared to normal males (1X2A). In superfemales (3X2A) carrying an extra X-chromosome the transcription in each of the X-chromosomes proceeds with the same rate as in diploid (2X2A) or triploid (3X3A) females. In intersexes (2X3A) the rate of transcription in each of X-chromosomes is intermediate between male and female levels. — The comparison of transcription rates in X-chromosomes with the levels of two enzymes coded for by sex-linked genes in males, females, super-females and intersexes (Faizullin and Gvozdev, 1972, 1973) revealed that the dosage compensation of the enzyme synthesis is effected at the level of transcription.
21 citations
TL;DR: It is shown that the apparent incompleteness of dosage compensation when RNA synthesis is measured autoradiographically is not due to the existence of contiguous dosage compensated and non-dosage compensated genes, but seems to be the result of peculiarities in the coordination of RNA synthesis between the X chromosomes and autosomes.
Abstract: It is shown that the apparent incompleteness of dosage compensation when RNA synthesis is measured autoradiographically is not due to the existence of contiguous dosage compensated and non-dosage compensated genes Rather this seems to be the result of peculiarities in the coordination of RNA synthesis between the X chromosomes and autosomes The slope of the line defined by \([\bar X]_i \) and \([\overline {2R} ]_i \) (number of grains over the X and autosomal segments averaged over the different nuclei assayed in each gland) is indistinguishable in males and females (apparent complete dosage compensation) An average of the slopes obtained for different individual glands (from [X] and [2R], the grain counts over each nucleus belonging to a particular gland), on the other hand, has a value in males which is approximately half of the value attained by females (a value of one half, in males, indicates dosage effect since males have one X and females have two)
9 citations
TL;DR: Analysis of the degree of homology of the chromosomes confirmed that, in the derived polyploid lines, part of the genome is in a triploid condition (Oliveri et al. 1972) even if in some cases only parts of the chromosome are in aTriploids condition as a result of deletions.
Abstract: SUMMARYThe authors have examined the « banding pattern », revealed by the Seabright method (1972), of chromosomes of an aneuploid-diploid line (C-125) and of certain lines of various degrees of ploidy derived from it. It was found that the line C-125 has preserved a large proportion of normal chromosomes, similar to those of the species, some in a diploid and others in a haploid condition.Analysis of the degree of homology of the chromosomes confirmed that, in the derived polyploid lines, part of the genome is in a triploid condition (Oliveri et al. 1972) even if in some cases only parts of the chromosome are in a triploid condition as a result of deletions. This last type of chromosome rearrangement is the one that has had the greatest importance in the evolution of the karyogram of the induced polyploid lines. The results are discussed in relation to problems of « dosage compensation ».
5 citations