198 PROGESTERONE, ESTROGEN (ER-α AND ER-β), AND OXYTOCIN RECEPTOR GENE EXPRESSION IN CANINE EMBRYOS

Abstract

The aim of this study was to compare the mRNA levels of hormone receptor for progesterone (PR), oestrogen α (ER-α), oestrogen β (ER-β), and oxytocin (OTR) in canine morulae and blastocysts. Ten healthy mature bitches were inseminated based on monitoring vaginal cytology and progesterone concentration. The first insemination was performed on Day 2 after the preovulatory LH surge (progesterone 4 ng mL^–1), and the second was performed 48 h later. All females were submitted to ovariohysterectomy (OVH), and the oviduct as well the uterurs were flushed with PBS solution to obtain the embryos. The females were divided into two groups: Group A (n = 5), morulae were collected 8 days after the LH surge and Group B (n = 5), blastocysts were collected 12 days after the LH surge. The pools (n = 10) of embryos (5 embryos/pool) were stored in RNAlater^® (Ambion, Life Technologies, USA) at –80°C. The samples were analysed together. The RNA later was removed used PBS calcium free and the total RNA extraction was performed using the Qiagen RNeasy micro-kit (Hildesheim, Germany). Before reverse-transcription (RT) reaction, the total RNA was treated with DNase I Amplification Grade (Invitrogen Life Technologies, Carlsbad, CA, USA). The gene expression of target genes was assessed by real-time RT-qPCR, using SuperScript III for RT and power SYBR Green PCR Master Mix (Applied Biosystems, USA) for cDNA for PCR. The primers for target genes were designed using the software Primer Express^® (Applied Biosystems, USA). The gene expression of target genes was normalized by HPRT gene and the relative abundance of mRNA was determined by the ΔΔct method corrected by amplification efficiency using Pffafl’s equation. The means of mRNA relative abundance were compared by t-test. The PR mRNA expression only in blastocysts is similar to the results obtained by Hou et al. (1997) in rat embryos. It is believed that the absence of PR in the early stages of cleavage is due to the indirect action of progesterone by growth factors produced by the maternal reproductive tract (2). Apparently, ER-β action does not occur in the embryo canine phases analysed; however, the action of ER-α seems related to the deployment signal as seen by Hou et al. (1996) in rats. Similarly to findings in the literature, OTR expression decreased in canine embryonic development. This receptor was produced by blastocysts while present in the uterus, which may represent an incidental mechanism to the embryo control of endometrial receptivity, such as also to prevent the development of endometrial luteolytic mechanism. The variation in hormone receptors gene expression in canine embryos can be influencing the transition from morula to blastocyst. In addition, a hormonal influence on these structures can occur in different ways.