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Rat spermatid basic nuclear protein TP3 is the precursor of protamine 2
E Unni1, Y Zhang, M L Meistrich
1Department of Experimental Radiotherapy, University of Texas M.D. Anderson Cancer Center, Houston 77030.
Experimental Cell Research
|January 1, 1994
Summary
Rat sperm P2 precursor protein is synthesized but not fully processed. Impaired processing leads to loss of protamine P2 from rat sperm chromatin during maturation.
Area of Science:
- Reproductive Biology
- Molecular Biology
- Spermatogenesis
Background:
- Protamine P2 is a key sperm nuclear protein, present in mature sperm of some mammals but absent in others, like the rat.
- The rat possesses the gene for P2 but lacks mature P2 in sperm, suggesting a post-transcriptional regulatory mechanism.
Purpose of the Study:
- To investigate the synthesis, processing, and localization of protamine P2 precursor in rat spermatogenesis.
- To compare P2 processing in rats with that in other mammals, such as mice.
Main Methods:
- Immunoreaction with an antibody to human P2.
- Microsequencing of amino-terminal ends of protein bands.
- Quantitation of precursor molecules in late spermatids.
Main Results:
- The rat P2 precursor, identified as TP3, is synthesized in late spermatids and immunoreacts with anti-P2 antibody.
- TP3 is the primary translational product of the rat P2 gene, with cleavage occurring similarly to mice.
- Significant levels of P2 precursor are found in rat late spermatids, but processing is impaired, leading to loss from chromatin in spermatozoa.
Conclusions:
- Rat spermatids synthesize protamine P2 precursor (TP3) but exhibit impaired processing.
- Defective P2 maturation results in its loss from the sperm chromatin, explaining its absence in mature rat sperm.