Embryo implantation in the uterus is an essential process for successful pregnancy in mammals. In general, the endocrine system induces sufficient embryo receptivity in the endometrium, where adhesion-promoting molecules increase and adhesion-inhibitory molecules decrease. Although the precise mechanisms remain unknown, it is widely accepted that maternal–embryo communications, including embryonic signals, improve the receptive ability of the sex steroid hormone-primed endometrium. The embryo may utilize repulsive forces produced by an Eph–ephrin system for its timely attachment to and subsequent invasion through the endometrial epithelial layer. Importantly, the embryonic signals are considered to act on maternal immune cells to induce immune tolerance. They also elicit local inflammation that promotes endometrial differentiation and maternal tissue remodeling during embryo implantation and placentation. Additional clarification of the immune control mechanisms by embryonic signals, such as human chorionic gonadotropin, pre-implantation factor, zona pellucida degradation products, and laeverin, will aid in the further development of immunotherapy to minimize implantation failure in the future.

TEX101, a germ cell-specific glycosyl-phosphatidylinositol (GPI)-anchored glycoprotein, is associated with Ly6k during spermatogenesis in testis. Although both Tex101^−/− and Ly6k^−/− mice can produce morphologically intact spermatozoa, both knockout mice show an infertile phenotype due to a disorder of spermatozoa to migrate into the oviduct. Since Ly6k specifically interacts with TEX101, complex formation of TEX101/Ly6k appears to be potentially important for functional sperm production. This study evaluated the fate of Ly6k in the presence or absence of TEX101 to explore the molecular interaction of both GPI-anchored proteins in seminiferous tubules. The present study showed that: 1) Although Ly6k mRNA was detected, the protein was present at very low levels in mature testes of Tex101^−/− mice, 2) Ly6k mRNA level was within the normal range in Tex101^−/− mice, 3) Ly6k mRNA was translated into a polypeptide in the testes of Tex101^+/+ and Tex101^−/− mice and 4) TEX101, as well as Ly6k, are co-factors that affect to molecular expression. These results indicate that both TEX101 and Ly6k contribute to the post-translational counterpart protein expression at the cell membrane. This mechanism may be important in maintaining the production of fertile spermatozoa during spermatogenesis.

Summary: TEX101, a glycoprotein we recently identified, is primarily characterized as a unique germ-cell-specific marker protein that shows sexually dimorphic expression during mouse gonad development. Based on data obtained from molecular biological as well as immuno-morphological studies, we believe this molecule may play a role in the process underlying germ cell formation. However, many points remain unclear as the molecular characteristics and its physiological functions are far from being completely understood. To clarify the molecular basis of TEX101, we herein report a further biochemical characterization of the molecule using testicular Triton X-100 extracts from mice. Deglycosylation studies using endoglycohydrolases that deleteN-linked oligosaccharides (OS) from the molecule show that TEX101 is highly (approximately 47%)N-glycosylated. All potentialN-glycosylation sites within TEX101 are glycosylated and most of these sites are occupied by endoglycosidase F2-sensitive biantennary complex type OS units. In addition, an extremely low population among TEX101 possesses only endoglycosidase H-sensitive hybrid type OS units. In studies using phosphatidylinositol-specific phospholipase C against native testicular cells orTEX101transfectant, the enzyme treatment caused major reduction of the TEX101 expression on the cell, suggesting that TEX101, at least in part, is expressed as a glycosylphosphatidylinositol-anchored protein. Taken together, these findings will help elucidate the molecular nature of TEX101, a marker molecule that appeared on germ cells during gametogenesis.

The oviductal epithelium secretes specific glycoproteins that associate with the egg after ovulation. Several published reports including our preliminary studies have suggested that ovarian steroids regulate the secretion of oviduct-specific glycoproteins in several mammalian species. The objective of this study, using golden hamsters, was to analyze the hormonal effects on gene expression of these molecules more precisely during various hormonal conditions (estrous cycle, ontogeny, pregnancy, GnRH analogue treatment, and ovariectomy) by in situ hybridization. The message for the hamster oviduct-specific glycoprotein (HOGP) was detected by a digoxigenin-labeled single-strand specific DNA probe in paraffin sections. Data from these studies show the following. 1) In the oviduct, the signal was detected in both the perinuclear region and the basal region in the ampulla but was predominantly detected in the basal region in the isthmus. 2) The signal intensity was high in the ampulla compared with the isthmus. 3) During a normal estrous cycle, the message level was significantly altered between the estrous and diestrous stages in the ampulla but not in the isthmus. In addition, the signal did not disappear at any stage in either the isthmus or ampulla. 4) The HOGP message was first observed from around 14 days of age and then decreased in parallel with serum estradiol levels during aging. 5) The signal was also observed in the oviductal epithelium of pregnant animals at term and of postpartum animals. 6) When we treated the animals with TAP-144-SR (GnRH analogue) or performed an ovariectomy, which caused diminution of serum estradiol and progesterone levels, the message of HOGP was significantly decreased. Moreover, the message expression was greatly induced after estradiol administration to GnRH analogue-treated animals, whereas a high level of serum progesterone slightly inhibited HOGP message expression. These results suggest that elevation of the serum estradiol/ progesterone level affects the HOGP gene expression in the ampulla. However, a high serum estradiol level did not induce the gene expression rapidly, suggesting that an adequate serum hormonal level over a given period of time may be important for the HOGP gene expression.