Sperm-associated retroviruses in the mouse epididymis.

Abstract

Sperm adsorbed with retrovirus particles were recovered from the epididymis of apparently normal male mice. Epididymal semen from all four mouse strains examined was positive for retrovirus (105 to 108 particles per ,ug of protein) indicating that epididymal fluids and sperm may be important vehicles for murine retrovirus spread. Immunoblot analyses revealed that the banding patterns of electrophoretically separated epididymal viral proteins from the four strains of males were more similar to each other than to either xenotropic New Zealand Black virus or ecotropic Rauscher leukemia virus proteins. The results indicate that retrovirus particles, possibly a unique strain, are commonly expressed at relatively high titers in the reproductive tract of male mice and are sperm-associated.A complete understanding of the transmissibility of retroviruses requires understanding the interaction of retroviruses with reproductive tract and embryonic cells. Although a principal mode of transmission of acquired immune deficiency syndrome is through sexual contact with seminal fluid that contains human immunodeficiency virus (1-6; §), retrovirus infection of the human reproductive tract is not understood nor is it known if other retroviruses, animal or human, are spread through sexual contact with reproductive tract secretions. The detection of retroviral reverse transcriptase activity in cell-free epididymal fluids from several strains of mice (7) and reports of viral glycoprotein, gp70, expression in mouse epididymis (8) indicated that retrovirus particles may be common in the reproductive tract of male mice. Based on the amount of reverse transcriptase activity detected, virus concentration estimates were as high as 109 particles per Al of epididymal semen (7,9). Epididymal fluids could thus be an important vehicle for murine retrovirus spread. In addition, partially purified sperm retained some of the reverse transcriptase activity, implying an association between the sperm cells and the reproductive tract retroviruses. Spermbound retroviruses would have access to all the cells contacted by motile sperm, including oocytes.To begin to determine if murine retroviruses could be spread by sexual contact, we have examined epididymal semen from four mouse strains: two known to contain endogenous xenotropic retroviral gene sequences, New Zealand Black (NZB) and random-bred Swiss (10), and two known to contain endogenous ecotropic as well as xenotropic retroviral gene sequences, C57BL/6 and AKR (11). The results reported here indicate that retrovirus particles are common in mouse epididymal semen and are sperm-associated. MATERIALS AND METHODSMouse Strains and Epididymal Semen Preparations. Mature males, 6-12 weeks of age, or retired breeders were from VAF (virus-antibody free) stocks. Strains C57BL/6, AKR, and New Zealand Black (NZB) were from the Jackson Laboratories; Cox Swiss males were from Laboratory Supply (Indianapolis, IN). Semen from the cauda epididymis and ductus deferens was collected in buffer A [0.01 M Tris H...

Viruses in the Mammalian Male Genital Tract and Their Effects on the Reproductive System

“…These viruses are mostly endogenous retroviruses, but some exogenous infectious retroviruses (mouse ecotropic virus and Friend ecotropic virus) have also been described (254), and the association of retroviral particles with spermatozoa may lead to congenital infection. Murine leukemia virus has been found free in the seminal fluid, fixed to spermatozoa, and associated with macrophages (164,194). The main site of virus synthesis within the male genital tract is the epithelial cells lining the epididymis duct.…”

“…In mice, high concentrations of retroviral particles have been detected in the epididymal fluid (162)(163)(164). These viruses are mostly endogenous retroviruses, but some exogenous infectious retroviruses (mouse ecotropic virus and Friend ecotropic virus) have also been described (254), and the association of retroviral particles with spermatozoa may lead to congenital infection.…”

Epididymis is a principal site of retrovirus expression in the mouse.

“…For the castration experiments, CBA males were anesthetized and castrated unilaterally to deprive one epididymis of sperm but not testosterone; a suture was applied to tag the castrate epididymis. Six weeks later the castrate and intact epididymides were removed, and epididymal semen from the respective sides were pooled for assay of reverse transcriptase activity as described (1,2). Seminal vesicles were removed, weighed, and compared with those from three normal males as a measure of testosterone levels.…”

“…Retrovirus particles are present at high concentrations (10-'-108 particles per .g of protein) in the epididymal fluids of several strains of mice (1,2). The significance of the reproductive tract retroviruses to the host male or to sexual partners exposed to ejaculated epididymal viruses is unknown.…”

A Reverse Transcriptase-Dependent Mechanism Plays Central Roles in Fundamental Biological Processes

“…High levels of expression are instead characteristic of transformed cells [Deragon et al 1990;Friedlander and Patarca 1999], in undifferentiated states, e.g., preimplantation embryos [Poznanski and Calarco 1991;Packer et al 1993] and in embryonic tissues such as placenta [Mwenda 1993]. Other preferential sites of expression of retroviral/ retrotransposon genes are the mammalian genital tract [Kiessling 1984;Kiessling et al 1987;DeHaven et al 1998;Crowell and Kiessling 2007], male germ cell precursors [Branciforte and Martin 1994;Dupressoir and Heidmann 1996] and gametes [Kattstrom et al 1989;Nilsson et al 1992;Miller 2000]. These observations suggest that the retroelement gene machinery, and specifically the genes encoding RT, are in a transcriptionally competent state in undifferentiated, highly replicating cells, both normal (embryos) and transformed (tumors), while being barely expressed or silent in terminally differentiated tissues.…”