Developmental changes in chromosomal composition and template activity during spermatogenesis in trout testis

Developmental changes in the composition of isolated chromatins and their ability to support RNA synthesis have been studied in trout testes undergoing spermatogenesis artificially induced by gonadotropin injections. The template activity of chromatin from the testes at the start of maturation is approximately one-tenth that of deproteinized DNA, and this activity is maintained throughout early stages of maturation. The template activity then decreases markedly and declines to 2–3% of that of DNA. This change in chromosomal template activity is accompanied by an increase of histone content and a decrease of nonhistone protein content in chromatin. In later stages of spermatogenesis, histones are completely replaced by protamines. Lysine-rich histone I appears to be replaced last in this process. A further decrease of the chromosomal template activity is observed as the histone-protamine replacement proceeds. Native nucleoprotamine is completely inactive in support of RNA synthesis.