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Sex Chromosome Pairing and Fertility in the Heterogametic Sex of Mammals and Birds
Published in Christopher B. Gillies, Fertility and Chromosome Pairing: Recent Studies in Plants and Animals, 2020
Although the presence of the XY body in spermatocytes is almost universal among mammals,7 this body is not found in other vertebrates having heteromorphic sex chromosomes. Since mammals have a characteristic mechanism of gene dosage compensation by X-chromosome inactivation in the somatic cells of females, it has been suggested that XY body formation and sex chromatin are related processes, probably sharing some underlying mechanism.7 Since the Y chromosome is generally a small chromosome, the mass of the XY body is formed mainly by the condensed X chromosome. If inactivation of the single X chromosome is needed for the normal development of mammalian spermatogenesis, as assumed by Lifschytz and Lindsley,21 the sharing of a basic mechanism for spermatogenesis and gene dosage compensation might be advantageous in economizing biological information. As previously pointed out,7 the peculiar packing of chromatin fibers in the XY body of the mouse spreads out to an autosomal region which is joined to the distal part of the X chromosomal piece in Searle’s T(X;16)16H translocation.48 This effect mimics the “spreading of inactivation” effect found in somatic cells.7 The molecular mechanisms involved both in sex-chromatin formation and in the formation of the XY body remain largely unknown. Thus, it is difficult to assess the information on the reported difference in transforming ability of X-DNA from spermatogenic cells and from somatic cells.62
Aicardi Syndrome and Klinefelter Syndrome
Published in Dongyou Liu, Handbook of Tumor Syndromes, 2020
Gene dosage compensation involves genetic equalization through X-inactivation, which randomly silences one of the X-chromosomes in female cell and keeps the other X-chromosome transcriptionally active. In cases of X-chromosome aneuploidy, extra X-chromosome is similarly inactivated. However, two pseudoautosomal regions (PAR1 and PAR2) along with up to 15% of additional genes on the short arm of the X chromosome (Xp) escape inactivation and are expressed from both X-chromosomes. In males with Klinefelter syndrome, extra copies of these escapee genes are transcriptionally active, and their overexpressions modulate the related cellular and developmental pathways. Located at the terminal region of the short arms and consisting of 24 genes (including short-stature homeobox-containing gene on chromosome X or SHOX), PAR1 is required during male meiosis for X–Y chromosome pairing, a process which is known to have a critical function in spermatogenesis. PAR2 is situated at the tips of the long arms and contains four genes (Eif2s3x, Ddx3x, Kdm5c, Kdm6a).
Genetic counselling in Mendelian disorders
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
Although X-chromosome inactivation applies to most of the human X chromosome, there are loci where it does not apply. Such inactivation-exempt loci include those for the Xg blood group, steroid sulphatase and the SHOX gene, located in the terminal region of the X chromosome short arm, the pseudoautosomal region of Xp. Such loci are exempt from X-chromosome inactivation in females and have functioning Y homologues; they do not show ‘dosage compensation’ and are implicated as contributing to the phenotypes of the disorders of sex chromosome number, such as Turner (X0) syndrome, XXY and XXX, as there is no mechanism of dosage compensation.
Somewhere over the sex differences rainbow of myocardial infarction remodeling: hormones, chromosomes, inflammasome, oh my
Published in Expert Review of Proteomics, 2019
Kristine Y. DeLeon-Pennell, Merry L. Lindsey
X chromosome inactivation provides dosage compensation for X-linked genes between XX females and XY males [51]. For example, if a mother has a deleterious X mutation, the mutation is expressed in all cells of XY individuals but only half of the cells of XX individuals, making males more susceptible to X-linked mutations. Under normal conditions, a balanced gene expression between males and females is achieved due to X inactivation. However, X inactivation is not always 100% complete. In women, 15% of X chromosomal genes are overexpressed due to activation in both X chromosomes, while 3% are overexpressed in female mice [54]. Due to chromosomal differences, the use of mice may not fully recapitulate the role of the X chromosome. Spolarics et al. showed that blood neutrophils could be assessed for the X-linked protein marker glucose 6-phosphate dehydrogenase as a means to investigate female immune cell mosaicism using the unique inheritance pattern of X-linked polymorphisms [55]. Using an X-linked protein marker, cells can be separated and assessed for physiological differences linking mosaicism to changes in cellular function. Coupling this approach with a proteomics output would be a way to connect molecular to cell physiology.
Detection of a novel unbalanced X;21 translocation in a girl with Turner syndrome phenotype
Published in Gynecological Endocrinology, 2021
Elisavet Kouvidi, Sophia Zachaki, Nikoletta Selenti, Danai Veltra, Theodora Evmorfopoulou, Eirini Tsoutsou, Garifallia Tzifa, Christalena Sofocleous, Sarantis Gagos, Ariadni Mavrou
It is well known that in females, random inactivation of the one X chromosome (XCI) occurs in order to ensure dosage compensation between XX females and XY males [16]. Rarely, in cases with structurally abnormal X chromosome, XCI is nonrandom, in order to avoid a severe genomic imbalance. In the proband, the translocated X chromosome shows preferential inactivation retaining the normal X chromosome active.