Ullas KS, Pradeepa MM, Nikhil G, Rammohan N, Rao MR
Spatiotemporal Organization of AT and GC Rich DNA and Their Association With Transition Proteins TP1 and TP2 in Rat Condensing Spermatids. [JOURNAL ARTICLE]
J Histochem Cytochem 2009 Jun 8.
Transition proteins, TP1 and TP2, replace histones during mid-spermiogenesis (stages 12-15) and finally get replaced by protamines. TPs play a predominant role in DNA condensation and chromatin remodeling during mammalian spermiogenesis. TP2 is a zinc metalloprotein with two novel zinc finger modules, which condenses DNA in vitro in a GC preference manner. TP2 also localizes to nucleolus in transfected HeLa and Cos 7 cells suggesting a GC rich preference even in vivo. We have now studied the localization pattern of TP2 in the rat spermatid nucleus. Colocalization studies using GC selective DNA-binding dyes chromomycin A3 (CMA3) and 7-amino actinomycin D (AAD) and an AT-selective dye, 4', 6-diamidino-2-phenylindole (DAPI), indicate that TP2 is preferentially localized to GC rich sequences. Interestingly, as spermatids mature TP2 and GC rich DNA moves towards nuclear periphery and in the late stages of spermatid maturation TP2 is predominantly localized at the nuclear periphery. Another interesting observation is the mutually exclusive localization of GC and AT rich DNA in the elongating and elongated spermatids. A combined immunofluorescence experiment with anti-TP2 and anti-TP1 antibodies revealed several foci of overlapping localization indicating that TP1 and TP2 may have concerted functional role during chromatin remodeling in mammalian spermiogenesis.
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