Abstract: 505

IN UTERO PROTEINASE ACTIVITY DURING THE HAMSTER EMBRYO ZONA ESCAPE TIME WINDOW: AN IN VIVO MECHANISM OF ZONA LOSS.

DL Thrasher^{2 *}, SA Mese^{2 *}, BD Bavister^{1 *}, DS Gonzales^{1 2 *}
Dept of Animal Health & Biomedical Sciences, Univ of Wisconsin, Madison, Wisconsin ¹
Dept of Biology, Univ of Southern Colorado, Pueblo, Colorado ²

The mechanism of blastocyst escape from the zona pellucida in vivo is unknown, but is probably quite different from the commonly observed process of in vitro hatching. In vivo, hamster blastocysts escape from their zonae during a time window between 68-78 h post egg activation (PEA; approx. 2400-1200 h on the 4th day of pregnancy) by global zona lysis suggestive of uterine proteinase activity (Gonzales and Bavister, 1995, Biol Reprod 52:470-480). The goal of the present study was to investigate proteinase activity by zymography in uterine flushings collected during the zona escape time window in both pregnant and pseudopregnant hamsters. The prominent enzyme activities were estimated to be 71, 68 and 20 K_d in pregnant hamsters, and 71, 68 and 40 K_d in pseudopregnant hamsters. The appearance of these enzymatic activities in uterine flushings coincides with the zona escape time window, and are minimal or absent outside this time window. Further, we found that uterine flushings collected from pregnant females at 75 h PEA are also capable of zona lytic activity in vitro. In addition, we observed that unfertilized eggs in pseudopregnant females also lose their zonae during the same time period as the zona loss window of pregnant hamsters. These preliminary data indicate that there is an important uterine contribution to blastocyst escape from the zona pellucida, consisting of proteinases secreted during a brief time window prior to blastocyst attachment. In the absence of these uterine enzymes in vitro, blastocysts developing in culture media undergo hatching from their zonae pellucidae by another mechanism, at least partly involving mechanical rupture of the zona. Supported by NIH grants HD 22023 and 2S06 6M08197-17.

    This abstract is being presented on Tuesday, August 3 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.