POSTMEIOTIC TRANSCRIPTION OF X AND Y CHROMOSOMAL GENES DURING SPERMATOGENESIS IN THE MOUSE

During the meiotic prophase of spermatogenesis, the X and Y chromosome s form the heterochromatic sex body, showing little transcriptional ac tivity. It has been suggested that transcription of the Xist gene is i nvolved in this inactivation. After completion of the meiotic division s, at least two Y chromosomal genes, Zfy and Sry, are transcribed in h aploid spermatids. In contrast, postmeiotic transcription of X chromos omal genes has not been demonstrated. Using highly purified preparatio ns of mouse pachytene spermatocytes, round spermatids, and cytoplasmic fragments from elongated spermatids, the present experiments show dif ferential postmeiotic expression of the Y chromosomal genes Ubely and Sry, with highest mRNA levels in round spermatids and cytoplasmic frag ments, respectively. Postmeiotic transcription of the X chromosomal ge ne Ubelx is indicated by an increased level of Ubelx mRNA in round spe rmatids and cytoplasmic fragments. The X chromosomal gene MHR6A shows a marked temporary postmeiotic expression in round spermatids. This po stmeiotic activity of the X chromosome is a novel finding, which may h ave implications for our understanding of X chromosome inactivation du ring spermatogenesis and paternal genome imprinting. (C) 1995 Academic Press, Inc.