A novel uterine protein that associates with the embryonic capsule in equids.

This research discusses the identification of a new protein in the horse’s uterus that interacts with the embryonic capsule during the early stages of pregnancy. The protein is progesterone dependent, but stops being produced around day 20 of pregnancy, and may be crucial in pregnancy preservation.

Characterization of the Novel Protein

In this study, a unique protein was detected in enormous quantities in the mare’s endometrium— the innermost layer of the uterus. This protein appears to stick to, or become part of, the capsule devoid of cells that engulfs the equine conceptus during the early phase of pregnancy. It was scrutinized and sequenced in part. The protein had an estimated molecular weight of around 18 kDa when tested on SDS-PAGE gels. A sensitive carbohydrate detection kit revealed it was nonglycosylated.

• The initial 24 amino-terminal amino acids of the protein were compared with all database entries. Researchers found no significant identity with any known protein sequence, suggesting this is a distinctly novel protein.
• The protein’s secretive nature seems to rely on progesterone, as evidence of it correlated to peripheral serum progesterone profiles during the ovulation cycle.

The Role of the Protein in Pregnancy

The presence of the protein could be prompted in non-reproductive mares through the administration of synthetic progestagen, a man-made hormone similar to progesterone. Yet, despite ongoing high levels of progesterone in the serum, the protein leaves the uterus about day 20 into the mare’s gestation.

• The disappearance of the protein suggests that its synthesis and secretion are governed by additional mechanisms, not solely the presence of progesterone.
• The protein’s potent association with the glycoprotein capsule surrounding the equine blastocyst hints that it might integrate into the capsule when it expands on day 11 post-ovulation.

Potential Functions of the Protein

The protein not only could contribute to the structure of the embryonic capsule but might also have a role in sustaining pregnancy.

• One possibility, among others, is that the protein helps in the transportation of nutrients or other substrates through the capsule. This transport role could be crucial for the success of the pregnancy.