Fig. 3.

Comparison of in vitro and in vivo results for expression of X-linked genes. (A) X-inactivation gene expression data from human – mouse somatic cell hybrid system [2]. (B) Expression from inactive X chromosome using allelic expression assay in human fibroblasts [2]. (C) X-linked genes (n=217) analyzed from microarray gene expression database in 11 tissues [5]. The female/male (F/M) gene fold expression ratio (in vivo) from Son et al. [5] is shown for 217 X-linked genes in 11 tissues (1, adrenal; 2, cerebrum; 3, colon; 4, ileum; 5, kidney; 6, liver; 7, lung; 8, skeletal muscle; 9, spleen; 10, stomach; and 11, ureter). In (A) the X-inactivation status of the same 217 X-linked genes using nine somatic cell hybrids (in vitro) reported by Carrel and Willard [2] and demonstrated by a color code is also presented. Expression of a specific gene in 9/9 cell hybrids denotes significant gene expression for that gene from the inactive X (escaped inactivation), while 0/9 hybrids represented completely silenced genes. In general, no specific pattern was seen between the in vivo and the in vitro results. Relative expression levels of 43 of these genes from the inactive X chromosome in female human fibroblasts [2] are also shown by a color code (B).