ROGER T. LAMBERT A1
A1 School of Biological Sciences, University of Aberdeen, Aberdeen, AB24 2TZ, UK
During reactivation of the roe deer blastocyst from embryonic diapause, the conceptus secretes a unique protein. The conceptuses were cultured individually in vitro with a radiolabel to establish de novo protein synthesis. Endometrial tissue from the same does was also cultured in vitro to establish radiolabel incorporation into endometrial secretions during blastocyst reactivation. Incorporation into secretory proteins from the blastocysts showed a significant increase during reactivation (p < 0.05) whereas incorporation into endometrial secretory proteins remained constant. The secretory proteins from the conceptus were identified using electrophoresis and fluorography as having the same molecular weight and pI as pregnancy-associated glycoproteins (PAGs). Fluorography clearly identified a single PAG with a molecular weight of 66 kDa and an isoelectric point (pI) of 6.2. Previous research shows these blastocyst secretions target endometrial receptors. The current study demonstrates this is followed by a dramatic increase in concentrations of maternal estradiol in serum, from 1.07 ± 0.4 pg ml-1 during diapause to 49.17 ± 0.37 pg ml-1 at trophoblast elongation. Estradiol is the hormone responsible for triggering the endocrine events that lead to implantation. PAGs are released from trophoblast cells and bind to specific cell surface receptors on maternal target cells. The role for PAGs in trophoblast cells had not previously been defined. Data from this study demonstrate that embryonic programming initiates the transcription of specific genes in the inner cell mass of the blastocyst, messenger RNA directs synthesis of PAG in the trophoblast, and the roe deer-specific PAG triggers the maternal response by targeting endometrial receptors.
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