High impact information on XIST

• Analysis of NT and control pregnancies indicated disruption of genomic imprinting at the X inactivation-specific transcript (XIST) locus in the chorion, but not the fetus of clones, whereas proper allelic expression of the insulin-like growth factor II (IGF2) and gene trap locus 2 (GTL2) loci was maintained in both the fetus and placenta [1].
• Analysis of the XIST differentially methylated region (DMR) in clones indicated normal patterns of methylation; however, bisulfite sequencing of the satellite I repeat element and epidermal cytokeratin promoter indicated hypermethylation in the chorion of clones when compared with controls [1].
• In vitro production and nuclear transfer affect dosage compensation of the X-linked gene transcripts G6PD, PGK, and Xist in preimplantation bovine embryos [2].
• NT-derived blastocysts showed an increased Xist expression compared with that of IVP, in vivo-generated, and parthenogenetic embryos [2].
• In contrast, among the male tissues examined, Xist expression was detected only in testis [3].

Biological context of XIST

• X-inactive specific transcript (XIST), which is thought to be the central factor for the X-inactivation process in female mammals, is known to be expressed in males during spermatogenesis [4].
• Expression of the X-inactive specific transcript (XIST) gene is a prerequisite step for dosage compensation in mammals, accomplished by silencing one of the two X chromosomes in normal female diploid cells or all X chromosomes in excess of one in sex chromosome aneuploids [5].
• Our previous studies showing that XIST expression does not eventuate the inactivation of X-linked genes in fetal bovine testis had suggested that XIST expression may not be an indicator of X inactivation in this species [5].
• Whereas the FISH assignment of XIST indicates a similar location on the q-arm of the human and cattle X chromosomes, the locus of HPRT1 supported the assumption of a chromosome rearrangement between the distal half of the q-arm of HSAX and the p-arm of BTAX identified by RH mapping [6].
• Here we report the results of our strand-specific RT-PCR approach to identify the amplicon detected in fetal bovine testes previously referred to as XIST and to test for sense/antisense expression in male and female organs and cell cultures of different sex chromosome constitution [7].

Anatomical context of XIST

• XIST transcripts were detected in unsexed pools at the 8-16 cell stage, in male and female morulae, and in female blastocysts [8].
• Sex-linked genes are not silenced in fetal bovine testes expressing X-inactive specific transcript (XIST) [4].
• Our results showed that the transcript detected consistently in male gonads and variably in somatic organs represents XIST antisense RNA and that XIST sense and antisense RNAs are co-expressed in female somatic tissues and cultured cells including cells of sex chromosome aneuploids (XXY and XXX) [7].
• Finally, the pattern of expression of XIST in bovine oocytes and embryos was similar to that reported in humans [9].
• Expression of X inactive specific transcript (Xist) and testicular morphogenesis in bovine fetuses [10].

Other interactions of XIST

• Results showed that XIST expression was significantly higher (p < 0.05) in XXX cells compared to XX and XXY cells and that G6PD [5].

Analytical, diagnostic and therapeutic context of XIST

• Expression of XIST sense and antisense in bovine fetal organs and cell cultures [7].

References