Immunocytochemical detection of a murine leukemia virus-related nuclear antigen in mouse oocytes and early embryos

Human oocytes express murine retroviral equivalents

Unfertilized human oocytes expressed a gp70-related epitope as observed when staining section immunocytochemically with a panel of monoclonal antibodies against gp70 of murine leukemia virus. Some oocytes also expressed virus-like particles at the cell membrane. Follicular fluids, corresponding to these oocytes, contained p30- and gp70-related antigens, reverse transcriptase, and an increased titer of interferon. The three- to four-cell human cleavage stages did not contain the gp70-related epitope. It is concluded that human oocytes, but not early cleavage stages, express products that suggest the presence of an active endogenous retrovirus genome.

A retroviral gp70-related protein is expressed at specific stages during mouse oocyte maturation and in preimplantation embryos

Mouse monoclonal antibodies directed against different epitopes of the murine leukemia virus envelope protein gp70 were used to study the expression of retroviral related env proteins during mouse oocyte maturation, fertilization and blastocyst formation. A gp70-related antigen was detected with immunohistochemistry in growing oocytes but not in primordial and primary non-growing oocytes. Atretic oocytes were also negative. Both parthenogenetically activated and fertilized oocytes were positive. Two-cell stages showed a patchy distribution of the antigen. Later preimplantation stages were negative except for a markedly positive period during compaction of the morula and adhesion of the blastocyst.

Nuclear location of the putative transforming protein of avian myelocytomatosis virus

The putative transforming protein of avian myelocytomatosis virus MC29 is a 110,000 dalton (P110gag-myc) polyprotein comprised of sequences derived from both the gag region and the MC29-specific myc region. Two approaches have been taken to determine the location of the MC29 gag-related proteins in transformed cells: subcellular fractionation and immunofluorescence. Analysis of subcellular fractions of MC29-transformed cells by immunoprecipitation indicates that the majority of the gag-myc polyprotein is found in the nuclear fractions of Q8 cells (a nonproducer line of MC29-transformed quail embryo fibroblasts) and nonproducer cells derived from a liver tumor of MC20-infected quail. This is in contrast to the distribution of gag-related helper virus proteins lacking myc, which are found only in nonnuclear fractions of superinfected Q8 cells. The purity of unlabeled nuclei was assessed by electron microscopy and enzyme assays, revealing little contaminating material from other subcellular fractions. Immunofluorescence experiments using monospecific anti-gag serum showed specific, intense immunofluorescence in the nuclei of fixed Q8 cells. In contrast, the majority of P75gag-erb, a candidate transforming protein produced by avian erythroblastosis virus (AEV), is absent from the nuclei of nonproducer AEV-transformed chick embryo fibroblasts. The nuclear association of the MC29 transforming protein may be related to some of the unique properties of MC29-transformed cells.