Differences in the pattern of X-linked gene expression between fetal bovine muscle and fibroblast cultures derived...

The sex determination system in mammals creates an imbalance between males and females in the number of X chromosomes. This imbalance is compensated through transcriptional silencing of one of the two X chromosomes in female diploid cells by epigenetic modifications. Although common for mammals, X inactivation shows marked species-specific differences in mechanisms and end results, and provides a unique opportunity to study epigenetic regulation of gene expression. The aim of the present study was to establish the expression pattern of selected X-linked genes in bovine fetal muscle tissue and muscle fibroblast cultures in order to follow possible modifications at the transcriptional level attributable to in vitro culture. We used heterologous cDNA microarray hybridization and quantitative real-time PCR to study the pattern of expression of X-linked genes including SLC25A6, GAB3, MECP2, RPS4X, JARID1C, UBE1, BIRC4 and SLC16A2. Quantitative real-time PCR analysis in fetal bovine muscle showed higher transcript levels in females for all X-linked genes tested with the exception of SLC25A6, with differences being significant for RPS4X, JARID1C and UBE1. The expression in fibroblast cultures derived from the same samples differed, with significantly higher levels for UBE1, GAB3 and BIRC4, while the rest of the panel of X-linked genes remained unchanged. The changed expression pattern in vitro, probably reflecting modifications in the epigenetic mechanisms that regulate transcriptional activity and gene silencing in X inactivation, has important implications for the advancement of new biotechnologies such as somatic cell nuclear transfer and stem cell therapy.