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Abstract
Chromatin remodeling during spermiogenesis is
characterized by a series of nuclear protein replacements.
Histones are replaced by transition nuclear proteins,
which are in turn replaced by protamines. The transition
nuclear proteins, TP1 and TP2, and the protamines, PRM1
and PRM2, are the major nuclear proteins involved in this
process. Biochemical studies of mice with null mutations
in one of the Tnp genes showed that the absence of
one TP
led to an apparent elevation in the amount of the
remaining TP in the testis. To investigate the mechanism
of changes of protein levels and effects of one Tnp
mutation on other nuclear proteins, we used
immunohistochemistry techniques to determine the
distribution of these nuclear proteins. In contrast to
previous biochemical analyses, which indicated that
nuclear protein replacement was sequential with little
overlap between the protein types, we found considerable
overlap in the nucleoprotein types during spermiogenesis.
The TPs, which appear before histone displacement is
complete, were shared among genetically inequivalent
spermatids. The absence of one TP did not affect the time
of appearance of the other TP or of the protamines, but it
did affect the displacement of the other TP, leading to
its abnormal retention. The elevated levels of the
remaining TP in Tnp-mutant mice appeared to be a
consequence of the prolonged retention rather than
increased synthesis. Thus the absence of one of the TPs
did not significantly affect transcription or translation
of the other basic proteins but did affect
post-translational events.
Key words:
Testis •
Sperm •
Sperm maturation •
Spermatid •
Spermatogenesis
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