EXPRESSION OF AN AVIAN PROTAMINE IN TRANSGENIC MICE DISRUPTS CHROMATIN STRUCTURE IN SPERMATOZOA

The objective of this study was to determine the consequences of disru pting spermatozoal chromatin condensation on spermatozoal development and function. The avian protamine, galline, was targeted to spermatids of transgenic mice using the mouse protamine 1 gene promoter. Three t ransgenic mouse lines were established that expressed galline mRNA at 65%, 120%, and 185% of the level found in rooster testis. Galline mRNA accumulated in round spermatids to levels similar to that of mouse pr otamine and, as with the mammalian counterpart, translation was delaye d until the elongating spermatid stage. Protein gels revealed that gal line accumulated in mature spermatozoa whereas mouse protamines were r educed, suggesting that galline competes with protamines for binding t o spermatozoal DNA. Acridine orange binding analysis indicated that DN A of the transgenic spermatozoa was not as tightly packed as that of c ontrols. This was corroborated by electron microscopy, which revealed disruption of the normal dense chromatin structure of spermatozoal hea ds. Despite these perturbations of chromatin condensation, the transge nic spermatozoa were functionally normal, as the majority of transgeni c mice had normal fertility. However, in mice that expressed excessive galline, there was a gradual destruction of seminiferous tubules lead ing to infertility. Our findings suggest that very precise packaging o f DNA in germ cells may nor be essential for subsequent unpackaging in the pronucleus of fertilized eggs and for subsequent normal developme nt of the embryo.