PubMed · 9095520
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M J Telen. 1997. Coordinator's report--section 2D3.. https://doi.org/10.1016/s1246-7820(97)80029-8
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The XIST gene, expressed only from the inactive X chromosome, is a critical component of X inactivation. Although apparently unnecessary for maintenance of inactivation, XIST expression is thought to be sufficient for inactivation of genes in cis even when XIST is located abnormally on another chromosome. This repression appears to involve the association of XIST RNA with the chromosome from which it is expressed. Reactivated genes on the inactive X chromosome, however, maintain expression in several somatic cell hybrid lines with stable expression of XIST. We describe here another example of an XIST-expressing human-hamster hybrid that lacks X-linked gene repression in which the human XIST gene present on an active X chromosome was reactivated by treatment with 5-aza-2'-deoxycytidine. These data raise the possibility that human XIST RNA does not function properly in human-rodent somatic cell hybrids. As part of our approach to address this question, we reactivated the XIST gene in normal male fibroblasts and then compared their patterns of XIST RNA localization by subcellular fractionation and in situ hybridization with those of hybrid cells. Although XIST RNA is nuclear in all cell types, we found that the in situ signals are much more diffuse in hybrids than in human cells. These data suggest that hybrids lack components needed for XIST localization and, presumably, XIST-mediated gene repression.
Ovarian sex cord-stromal tumors are a morphologically diverse group of neoplasms that can mimic the appearance of other ovarian tumors. Because the treatment and prognosis of sex cord-stromal tumors differs substantially from those of other ovarian neoplasms, the development of an immunohistochemical panel to support the diagnosis of the former group of tumors would be useful. In this report, the utility of immunostaining for inhibin alpha, epithelial membrane antigen, MIC2 gene protein product, and keratin in the differential diagnosis of sex cord-stromal tumors was assessed in formalin-fixed, paraffin-embedded sections. In addition, the immunohistochemical staining pattern of ovarian small cell carcinomas (SCCs), hypercalcemic type, was analyzed in an attempt to clarify the histogenesis of these tumors. Thirty-two (97%) of 33 granulosa cell tumors (GCTs), 10 (91%) of 11 Sertoli-Leydig cell tumors (SLCTs), and 4 (8%) of 51 carcinomas showed inhibin alpha immunopositivity. None of the 3 lymphomas, 5 carcinoids, 6 dysgerminomas, or 12 SCCs showed inhibin alpha positivity. Eighteen (55%) GCTs, 6 (55%) SLCTs, 6 (12%) carcinomas, and 7 (58%) SCCs showed MIC2 gene expression. None of the GCTs and only one SLCT showed epithelial membrane antigen (EMA) positivity, although 92% of surface epithelial carcinomas and 75% of SCCs were immunoreactive. These data suggest that detection of inhibin immunoreactivity in an ovarian tumor that is EMA-negative provides both sensitive and specific support for the diagnosis of a sex cord-stromal tumor. Because SCCs generally stain for EMA but not for inhibin, it appears that SCCs probably represent a variant of surface epithelial tumor rather than a type of sex cord-stromal tumor.
We studied 2 subjects with a 45,X/46,X,ring(Y) karyotype. Both of them were evaluated because of short stature and a subnormal rate of linear growth. One patient had additional features of the Ullrich-Turner syndrome. Both subjects had normal male external genitalia. Two copies of the pseudoautosomal gene, MIC2, were present in DNA of each individual. All sequences examined on the Y-specific portion of the short arm, including those for the sex-determining region Y (SRY) gene, were present. By contrast, portions of the long arm of the Y chromosome were missing from DNA of both subjects. In subject 1, deletion intervals 6 and 7 were missing. In subject 2, deletion interval 5, distal to 5B, was missing in addition to intervals 6 and 7. The most likely explanation for the ring formation in these subjects is a chromosomal break in the long arm and in the pseudoautosomal region of the short arm distal to MIC2 with subsequent ligation of the remaining sequences on the long arm and short arm. However, a complex rearrangement cannot be excluded.