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Abnormal X: autosome ratio, but normal X chromosome inactivation in human triploid cultures.

ABSTRACT: X chromosome inactivation (XCI) is that aspect of mammalian dosage compensation that brings about equivalence of X-linked gene expression between females and males by inactivating one of the two X chromosomes (Xi) in normal female cells, leaving them with a single active X (Xa) as in male cells. In cells with more than two X's, but a diploid autosomal complement, all X's but one, Xa, are inactivated. This phenomenon is commonly thought to suggest 1) that normal development requires a ratio of one Xa per diploid autosomal set, and 2) that an early event in XCI is the marking of one X to be active, with remaining X's becoming inactivated by default.Triploids provide a test of these ideas because the ratio of one Xa per diploid autosomal set cannot be achieved, yet this abnormal ratio should not necessarily affect the one-Xa choice mechanism for XCI. Previous studies of XCI patterns in murine triploids support the single-Xa model, but human triploids mostly have two-Xa cells, whether they are XXX or XXY. The XCI patterns we observe in fibroblast cultures from different XXX human triploids suggest that the two-Xa pattern of XCI is selected for, and may have resulted from rare segregation errors or Xi reactivation.The initial X inactivation pattern in human triploids, therefore, is likely to resemble the pattern that predominates in murine triploids, i.e., a single Xa, with the remaining X's inactive. Furthermore, our studies of XIST RNA accumulation and promoter methylation suggest that the basic features of XCI are normal in triploids despite the abnormal X:autosome ratio.

SUBMITTER: Gartler SM

PROVIDER: S-EPMC1526452 | biostudies-literature | 2006 Jul

REPOSITORIES: biostudies-literature

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Abnormal X: autosome ratio, but normal X chromosome inactivation in human triploid cultures.

Gartler Stanley M SM Varadarajan Kartik R KR Luo Ping P Norwood Thomas H TH Canfield Theresa K TK Hansen R Scott RS

BMC genetics 20060703

<h4>Background</h4>X chromosome inactivation (XCI) is that aspect of mammalian dosage compensation that brings about equivalence of X-linked gene expression between females and males by inactivating one of the two X chromosomes (Xi) in normal female cells, leaving them with a single active X (Xa) as in male cells. In cells with more than two X's, but a diploid autosomal complement, all X's but one, Xa, are inactivated. This phenomenon is commonly thought to suggest 1) that normal development req ...[more]

PMID: 16817970

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Project description:BackgroundTriploid organisms have three sets of chromosomes. In Atlantic salmon, hydrostatic pressure treatment of newly fertilized eggs has been extensively used to produce triploids which are functionally sterile due to their unpaired chromosomes. These fish often perform poorly on commercial farms, sometimes without explanation. Inheritance patterns in individuals subjected to pressure treatment have not been investigated in Atlantic salmon thus far. However, work on other species suggests that this treatment can result in aberrant inheritance. We therefore studied this in Atlantic salmon by genotyping 16 polymorphic microsatellites in eyed eggs and juveniles which had been subjected to pressure-induction of triploidy. Communally reared juveniles including fish subjected to pressure-induction of triploidy and their diploid siblings were included as a control.ResultsNo diploid offspring were detected in any of the eggs or juveniles which were subjected to hydrostatic pressure; therefore, the induction of triploidy was highly successful. Aberrant inheritance was nevertheless observed in 0.9% of the eggs and 0.9% of the juveniles that had been subjected to pressure treatment. In the communally reared fish, 0.3% of the fish subjected to pressure treatment displayed aberrant inheritance, while their diploid controls displayed 0% aberrant inheritance. Inheritance errors included two eyed eggs lacking maternal DNA across all microsatellites, and, examples in both eggs and juveniles of either the maternal or paternal allele lacking in one of the microsatellites. All individuals displaying chromosome aberrations were otherwise triploid.ConclusionsThis is the first study to document aberrant inheritance in Atlantic salmon that have been subjected to pressure-induction of triploidy. Our experiments unequivocally demonstrate that even when induction of triploidy is highly successful, this treatment can cause chromosome aberrations in this species. Based upon our novel data, and earlier studies in other organisms, we hypothesize that in batches of Atlantic salmon where low to modest triploid induction rates have been reported, aberrant inheritance is likely to be higher than the rates observed here. Therefore, we tentatively suggest that this could contribute to the unexplained poor performance of triploid salmon that is occasionally reported in commercial aquaculture. These hypotheses require further investigation.

Dataset Information

Abnormal X: autosome ratio, but normal X chromosome inactivation in human triploid cultures.

Publications

Abnormal X: autosome ratio, but normal X chromosome inactivation in human triploid cultures.

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