SPERM CELLS AND FOREIGN DNA - A CONTROVERSIAL RELATION

Sperm cells from a variety of species share the spontaneous ability to take up foreign DNA. That feature has been exploited to generate gene tically modified animals with variable efficiency in different species . An unexpectedly large set of factors appears to modulate the interac tion of sperm cells with exogenous DNA. The binding is mediated by spe cific DNA-binding proteins and is antagonized by an inhibitory factor in the seminal fluid. A portion of sperm-bound DNA is internalized in nuclei, a process mediated by CD4 molecules. Sperm interaction with fo reign DNA triggers endogenous nuclease(s) that cleaves both the exogen ous and the genomic DNA, eventually leading to a cell death process wh ich resembles apoptosis. Internalized foreign DNA sequences reach the nuclear matrix and undergo recombination with chromosomal DNA. From th ese studies, a surprising network of metabolic functions is beginning to emerge in mature spermatozoa, which are normally repressed and are specifically activated upon exposure to appropriate stimuli. (C) 1998 John Wiley & Sons, Inc.