ABSTRACT
The mammary epithelium coordinates the uptake of milk precursors and the transport of milk components in order to produce milk of relatively constant composition at a particular stage of lactation, as long as the mammary gland is healthy. The mammary epithelial cell controls the uptake of blood-borne molecules at its basal side and the release of products into milk at its apical side, through mechanisms of internalization (endocytosis) and mechanisms of release (exocytosis). These events are strictly dependent on the physiological stage of the mammary gland. This review addresses the mechanisms responsible for these processes and points out new questions that remain to be answered concerning possible interconnections between them, for an optimal milk secretion.
ABSTRACT
Cytokines and growth factors play important roles in implantation and maintenance of pregnancy, but also during early development. Among them interferon-gamma (IFNgamma) is highly expressed by mammalian trophoblast cells during implantation and seems to be involved in some cases of pregnancy loss. In the present study we investigated the possible presence of IFNgamma receptors (IFNGR) on mouse oocytes and preimplantation embryos. The two receptor chains IFNgammaRalpha (IFNGR-1) and IFNgammaRbeta (IFNGR-2) have been detected by indirect immunofluorescence at the surface of mouse oocytes (in germinal vesicle and metaphase II stages), as well as at all stages of in vitro embryo development from the one-cell to blastocyst stage. IFNGR appeared to colocalize partly with ganglioside GM1 at the cell surface of oocytes and embryos, indicating a possible preferential localization of this receptor in "rafts" microdomains. This was analyzed in more detail using software developed in the laboratory. IFNgamma was found to bind to its receptor at all stages analyzed. RT-PCR and Southern blot experiments confirmed the presence of the transcriptionally regulated IFNGR-2 chain mRNA, in mouse oocytes and preimplantation embryos. These results show, for the first time, that mouse oocytes and preimplantation embryos bear a complete and theoretically functional IFNGR, suggesting that this cytokine could play a role during early development.