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Variability of sperm histones in Anura contrasts with relative constancy in Urodela, Squamata and Aves

University of British Columbia

Sperm histone diversity in the vertebrates has been examined in order to delineate possible macroevolutionary trends. Sperm basic proteins have been characterized cytochemically in testis sections and by electrophoresis in polyacrylamide and starch gels. Representative species of Anura (frogs and toads), Urodela (newts and salamanders), Squamata (lizards and snakes) and Aves (birds) have been compared. The testis-specific basic proteins of Anura demonstrated a high degree of diversity. Cytochemically, sperm histones of the genus Rana resembled those of somatic cells while those of the genera Hyla, Bufo and Scaphiopus appeared to be of the more basic "intermediate type". Electrophoresis revealed differences between the testis-specific basic proteins of these genera, and in the genus Xenopus, sperm nuclear proteins varied at the species and even sub-species levels. X. tropicalis and X. so. n. Ill (Zaire), distantly related to the rest of the genus, were found to have somatic-like sperm histones as opposed to the intermediate type proteins displayed by other Xenopus species. The array of basic proteins found in the sperm of urodeles, reptiles and birds appeared more conservative than in anurans. All the urodeles studied showed a cytochemically detectable transistion from somatic histones to stable protamines to protamines during the course of spermiogenesis. The protamine-like protein appeared to be electrophoretically similar in all urodele species. Lizards and snakes also demonstrated testis- and sperm-specific basic proteins with similar electrophoretic mobilities, although cytochemistry suggested that the lizard sperm histones had a higher content of arginine than the proteins found in snake sperm. Cytochemically, the sperm nuclear proteins of seven species of birds, representing four avian orders, were found to be of the protamine type. Intact protamines were difficult to isolate from avian testes but similarities were noted between the major testis-specific electrophoretic bands of all the birds studied. Overall, there appeared to be a trend in vertebrate phylogeny from sperm histone diversity in teleost fish and anuran amphibians to relative constancy in Urodela, Reptilia, Aves and Mammalia. This evolutionary trend was discussed in terms of the possible, functions of the basic nuclear proteins of sperm and the appearance of internal fertilization and chromosomally-based sex-determination in the vertebrates.

Text

2010-03-26

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http://hdl.handle.net/2429/22515

Zoology

University of British Columbia

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