Novel genes induce uterine receptivity: the characterization of a specific gene product in the ewe uterus

Abstract

The normal environment of a sheep uterus is hostile and does not favor embryo growth. Through embryo transfer studies, it has been shown that the steroid hormones estrogen and progesterone allow the uterus to support and nurture developing embryos. However, genes important to uterine receptivity are relatively uncharacterized. In previous experiments, the technique of Differential Display-Polymerase Chain Reaction was used to identify novel endometrial genes that are expressed in receptive versus non-receptive uteri. Uterine samples from Day 3 and Day 6 of the estrous cycle were examined. Embryo transfer studies indicate that an embryo can be transferred to a uterus that differs at most twenty-four hours. Therefore, a Day 3 embryo cannot survive in a Day 6 uterus and vice-versa. One product, DD5, was found specific to a Day 6 uterus. A partial cDNA fragment of approximately 230 bases was isolated. Northern analysis revealed that DD5 is approximately 900 bases long. A complementary DNA library was constructed using both oligo-end labeling and random-prime probes involving the original DD5 fragment. A Bacterial Artificial Chromosome was also used to sequence DD5. Expression of DD5 in the uterus was examined for Day 1, 3, 5, 6, and 7 of the cycle using uterine cross-sections that were radioactively labeled with the partial DD5 sequence. The expression in the glandular epithelium was noted. The pattern of expression of DD5 was compared to that of the estrogen receptor. A partial sequence of the top strand of DD5 at the 3' end was determined. The position of the poly-A tail was confirmed, indicating that the sequence was at the 3' end. A database search indicated that the 3' region aligned with known ESTs. The complementary DNA library results were inconclusive. Expression of DD5 was high in a Day 5, 6, and 7 uterus, but not evident in a Day 1 or 3 uterus. The glandular epithelium region demonstrated the most significant expression. The glands closest to the lumen had the highest DD5 expression, with the superficial glandular epithelium having the highest.