292 EXPRESSION PROFILES OF STRESS AND METABOLIC MARKER GENES DURING IN VITRO PRODUCTION OF BUFFALO (BUBALUS BUBALIS) EMBRYOS

Abstract

An increased understanding of the pre-implantation embryo developmental stage, with respect to physiological interaction of embryo with its micromilieu both in vivo and in vitro, is imperative to comprehend the events of pre-implantation development.The objective of the present study was to examine the temporal expression of heat shock protein 70 (Hsp-70) and glucose transporter 1 (Glut1) genes in pre-implantation-stage buffalo embryos produced under the standard in vitro production (IVP) system. Embryos were produced from slaughterhouse ovaries employing standard in vitro embryo production protocol, and presumptive zygotes produced following IVM/IVF were cultured in vitro in mSOF under mineral oil; FCS (10%) was added at 48 h post-insemination (hpi).The time series of development at stages being zygote (18-20 hpi), 2-1 cell (48 hpi), 8-16 cell (94-96 hpi), morula (120-144 hpi), and blastocyst (168-192 hpi), pre-implantation embryos conforming to the above developmental pattern were considered as 'fast-cleaving embryos', and all the embryos that did not conform to the above developmental timing were regarded as 'slow-cleaving embryos'. Pools of immature oocytes (IM, 120), Matured oocytes (MO, 120), 8-16 cell stages (8-16, 70), morula (M, 28), and blastocyst (B, 9) were collected and prepared for total RNA isolation and RT-PCR for the specific transcripts, with ²-actin as loading control. The total RNA content ranged from 2.5 to 5.0 ng per oocyte/embryo. Presence of Hsp 70 and Glut1 gene transcripts was assessed in different stages of buffalo pre-implantation embryos using primers designed from bovine Hsp 70 and Glut1 by using the OLIGO program. RT was standardized using the embryo equivalent of 1-10 oocytes/embryo as the template as described by Arcellana-Panlilio and Schultz 1993 (Methods Enzymol. 225, 303-328) with PCR conditions being 59°C and 62°C for 45 s with 39 cycles for Glut1 and Hsp 70 gene transcripts, respectively. Amplicons were subjected to restriction digestion and sequencing (Acc. No. AJ812563, AJ812564). The expression of Hsp 70 throughout pre-implantation development in the fast-cleaving embryos indicated their maternal and zygotic origin, but transcripts of the Hsp 70 gene, represented by a single 488-bp amplicon, were not detected in slow-cleaving embryos, suggesting altered zygotic expression. Glut1 expression was prominent from the 8-16 cell stage, indicating a metabolic shift from pyruvate to glucose after the pre-compaction stage. For slow-cleaving embryos, transcripts of the Glut1 gene, represented by a single 327-bp amplicon, were absent during morula- and blastocyst-stage embryos, indicating the poor developmental competence of these embryos, which morphologically appeared normal. These transcription patterns reflect the embryonic response to the in vitro culture conditions and also correlate with the embryo quality and the speed of development of the pre-implantation buffalo (Bubalus bubalis) embryos.