CHROMATIN CONDENSATION BEHAVIOR OF THE Y-CHROMOSOME IN THE HUMAN TESTIS .1. EVIDENCE FOR DECONDENSATION OF DISTAL YQ IN GERM-CELLS PRIOR TOPUBERTY WITH A SWITCH TO SERTOLI CELLS IN ADULTS

The condensation behaviour of the human Y chromosome in germ cells and Sertoli cells of pre- and post-pubertal testes was followed by fluore scence in situ hybridisation using probes for three different regions of the Y chromosome. Patterns of expansion or contraction of signal ar e taken to reflect degrees of condensation of the related Y chromatin and hence its potential for genetic activity. For probe pHY2.1, which labels the distal non-fluorescent and fluorescent heterochromatin of t he Y chromosome (Yq12), an expanded signal seen in gonocytes of the pr epubertal testis is superseded by a condensed signal seen in adult ger m cells at all but the zygotene stage of meiotic prophase when meiotic pairing takes place. In contrast, Sertoli cells show a condensed sign al pre-pubertally but a greatly expanded signal in the adult testis. A totally condensed pHY2.1 signal is found in a chromosomally normal ma n with Sertoli-cell-only syndrome. It is hypothesised that control ove r at least some facets of spermatogenesis may not, in the adult, be au tonomous to the germ cells, but rather may emanate from the Sertoli ce lls. Chromatin expansion at zygotene could, however, be important for pairing and crossing over in the XY bivalent, successful synapsis ensu ring survival of spermatocytes into the post-meiotic stages.