Expression of Retinoid X Receptor Transcripts and their Significance for Developmental Competence in In Vitro‐produced Pre‐implantation‐stage Bovine Embryos

Abstract

Retinoid X receptors are frequently implicated in their role in embryonic development. However, there is no report regarding their expression in embryos with different qualities. In this study, expression pattern and levels of retinoid X receptor transcripts in different qualities and stages of in vitro-produced pre-implantation bovine embryos were examined using real-time polymerase chain reaction (PCR) techniques. Four independent cDNA pools per sample were prepared from mRNAs isolated from different developmental-stage embryos, after classifying them to be of good and bad quality. Primers were also designed to amplify products with PCR. Based on analysis, except retinoid X receptor gamma (RXRG) transcripts, the remaining two types (alpha and beta forms) were expressed in all samples with significantly higher (p < or = 0.05) levels until the eight-cell stage compared with the stages thereafter. However, the transcript levels for bad-quality embryos were consistently lower in all cases in comparison with good-quality embryos. RXRG was identified in 39% of the samples, but all in the pre-embryonic genome activation development stage. Therefore, strong expression patterns of these transcripts in earlier stages indicates their possible role during the maternal phase of embryo development, and the variations of copy number in embryos with different qualities substantiates their possible candidacy as potential quality markers. Moreover, identifying the transcript variations in different qualities and expression of RXRG at these stages is a novel input to the pre-implantation-stage knowledge.

Retinoid receptor-specific agonists regulate bovine in vitro early embryonic development, differentiation and expression of genes related to cell cycle arrest and apoptosis

“…According to the literature, transactivation often increases the expression of genes that are normally silent in the absence of their ligands. Transcripts of all retinoid subtypes of RXR and RAR (except for RARb) are expressed during the preimplantation stages in bovine embryos produced in vitro [5][6][7]. Immunostaining techniques have detected RARa, RARg-2 and RXRb in blastocysts [5,6] and RARa and RXRb in cumulus cells [8].…”

Expression Profile of Fatty Acid Metabolism Genes in Preimplantation Blastocysts of Obese and Non-Obese Mice

“…In adult tissues, this transcription factor is expressed. The mouse is not the only species with this transient lack in expression as Rxrg transcripts in bovine blastocysts were only detectable in some but not all analyzed embryos [35,36]. Surprisingly, Rxrg expression is positively correlated with the developmental competence of an embryo [36].…”

The Role of Peroxisome Proliferator‐Activated Receptors in the Development and Physiology of Gametes and Preimplantation Embryos

“…RXR α , RXR β , and RALDH 2 (one of the two enzymes oxidizing retinol to retinoic acid) are detected in all stages of preimplantation bovine embryos, including blastocysts which express RXR β protein in the inner cell mass and the trophectoderm [30]. RXR α , β , and γ transcripts in preimplantation bovine embryos are likely of maternal origin because eight-cell stage and earlier embryos have significantly higher RXR levels than later stage embryos [37]. Furthermore, RXRs may be essential for optimal embryo development because “good-quality” embryos express significantly higher levels of RXR transcripts than “bad-quality” embryos [37].…”

“…RXR α , β , and γ transcripts in preimplantation bovine embryos are likely of maternal origin because eight-cell stage and earlier embryos have significantly higher RXR levels than later stage embryos [37]. Furthermore, RXRs may be essential for optimal embryo development because “good-quality” embryos express significantly higher levels of RXR transcripts than “bad-quality” embryos [37]. It can be summarized that RXR expression in preimplantation embryos described above is corroborated by the expression of its partner, PPAR (discussed later).…”