Gordon H. Dixon

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

Abstract 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.

Nucleic Acids and Protamine in Salmon Testes

Publisher Summary This chapter focuses on the presence of nucleic acids and protamine in Salmon testes. It highlights the approach of the centenaries of the discoveries of deoxyribonucleic acid (nuclein) and of protamine. The subsequent relative lack of research on the biochemistry of the salmon testes is in all probability because of the limited geographic distribution of salmonoid fish together with the small fraction of the year when fish are available in the appropriate physiological condition. The chapter presents information on salmon sperm nucleic acids and protarnine pertinent to current interests in molecular biology. Among areas of considerable interest are the replication of DNA during spermatogenesis and the role of nucleases in replication, together with the studies of possible biochemical differences between the mitotic and meiotic (reduction) divisions. The small size and unusual composition of protamine invite a detailed study of its mechanism of biosynthesis, particularly whether the late “turning-on” of the synthesis is controlled at the transcriptional or translational level. Additionally, the biochemistry of the action of protein and steroid hormones can be studied. The spermatozoon itself offers a unique opportunity to study a free-living, highly differentiated cell from a higher organism, possessing characteristic organelles, but with nuclear genes in an inactive state until the events of fertilization reactivate the male genetic material.

Enzymatic Modification of Basic Chromosomal Proteins in Developing Trout Testis

During the differentiation of trout testis cells, there are major changes in the complement of basic chromosomal proteins bound to DNA. At a specific stage in development, new, sperm-specific, highly arginine-rich proteins-the protamines-are synthesized on small cytoplasmic polysomes, phosphorylated on their seryl residues by a cyclic AMP-dependent protein kinase and rapidly transported into the nuclei of spermatid cells. After binding to chromatin, the protamines progressively replace the histones on DNA, transforming nucleohistone into the very much more compact nucleoprotamine. During this replacement the O-phosphoryl groups of protamine are removed and, in the mature sperm, de-phospho-protamines become the sole basic proteins in complex with DNA.