146 EFFECT OF MATERNAL AGE AND PARITY ON THE PRESENCE AND DISTRIBUTION OF CADHERIN-E IN HAMSTER EMBRYOS DURING PRE-IMPLANTATION DEVELOPMENT AND TRANSPORT
Authors: Trejo A. , Navarro-Maldonado C. , Jimenez F. , Rosado A. 
Published: December 2006

Our knowledge of the factors that contribute to in vivo embryo development and transport are still incomplete. Although there is solid evidence that the hormonal state of the female regulates ovum transport in mammals, recently, because of significant differences between the rate of oviduct transport of fertilized and unfertilized eggs in several mammalian species, there have been some reports showing that the conceptus itself may auto regulates its own transport. During the initial phases of embryonic development the distribution of E-cadherin, a calcium dependent cell adhesion molecule, changes from a general distribution over the whole surface of the blastomeres to become almost exclusively localized over the points of contact between blastomeres. This change on E-cadherin localization has been related to the beginning of embryo compactation and is considered as the initial stage of differentiation. We have recently shown that pre-implantation embryo development and transport is highly synchronous in nuliparous young females (NYF), but not in adults. Nuliparous adult (8 months) females (NAF) and multiparous adult females (MAF) show significant asynchrony and retard on early embryo development. In NYF, all 8 cells embryos reached the uterus by 62 h after coitus. In adult females, both nuliparous and multiparous, a considerable number of 8 cells embryos fail to migrate into the uterus even at 67 h after coitus. E-cadherin distribution was studied by indirect immunofluorescence and confocal microscopy during preimplantation embryo development in three groups, NYF, MAF, and NAF, of regularly cycling golden hamster (Mesocricetus auratus) females. Females were mated with males of proven fertility. Only 15 minutes were allowing for mating. Time of ejaculation was registered. Females were sacrificed from 60 to 69 h after coitus. Corpora lutea were counted in both ovarian surfaces. Oviducts and uterine horns were flushed separately and embryo number, stage of development, and distribution were recorded. Cell numbers, cadherin distribution and the number of cadherin-dependent cell to cell contacts were established in at least 20 embryos per group and at each of the different hours of the study. Presence and distribution of E-cadherin on 4-, 6-, and 8-cell blastomeres embryos differs accordingly with the parity and age of the females. Differences are particularly important at the eight-cell stage 80 to 93% of the embryos from NYF showed normal cadherin dependent cell contacts with all neighboring cells. In the case of multiparous adult females (MAF) only 52 to 68% of the embryos showed normal cell to cell contacts. These results will be discussed in relation to the respective role that the female hamster and the conceptus itself play in early embryo development and transport. Our results also indicate that in spite of the significantly higher ovulation rate of old females, their reproductive efficiency were significantly lower than that of NYF.