SEQUENTIAL EXPRESSION OF NUCLEOPROTEINS DURING RAT SPERMIOGENESIS

Transition proteins and protamines are highly basic sperm-specific nuc lear proteins that serve to compact the DNA during late spermiogenesis . To understand their sequential role in this function, transition pro tein I (TP1), transition protein 2 (TP2), and protamine 1 (P1) were as sayed by polyacrylamide gel electrophoresis in pools of microdissected , staged seminiferous tubule segments in the rat, The results were com pared with immunocytochemical analyses of squash preparations from acc urately identified stages of the epithelial cycle. TP2 was the first t o appear as a faint band at stages IX-XI, followed by high levels at s tages XII-XIV of the cycle, TP1 showed a low expression at stage XIV o f the cycle and peaked at stages XIII-I, whereas protamine 1 first app eared at stage I of the cycle and remained high throughout the rest of spermiogenesis. Immunocytochemical analyses and Western blots largely confirmed these results: TP2 in steps 9-14, TP1 in steps 12-15, and P 1 from late step 11 to step 19 of spermiogenesis. We propose that TP2 is the first nucleoprotein that replaces histones from the spermatid n ucleus, and its appearance is associated with the onset of nuclear elo ngation. TP1 shows up along with the compaction of the chromatin. The two transition proteins seem to have distinct roles during transformat ion of the nuclei and compaction of spermatid DNA. (C) 1996 Academic P ress, Inc.