Multiple-embryo transfer for studying very early maternal–embryo interactions in cattle

Abstract

In the present paper, we highlight the need to study very early maternal-embryo interactions and discuss how these interactions can be addressed. Bovine species normally carry one or, less frequently, two embryos to term; there are very rare cases of triplets or higher-order multiple pregnancies in which all the offspring are born alive. Multiple-embryo transfer (MET) in cattle allows for the detection of endometrial responses in scenarios where single-embryo transfer would not. Although MET is non-physiological, the present study shows that at the very early embryonic stages, a uterus carrying zona-enclosed embryos does not exhibit non-physiological reactions. On the contrary, MET should be considered the sum of multiple individual effects triggered by developing embryos. We provide arguments to support our hypothesis that describe a rationale for current work with MET, and we discuss alternative hypotheses. Using cattle as a model, we describe how technical approaches to analyzing zona-enclosed early embryo-maternal interactions (i.e., transcriptomics, proteomics, and endometrial cell culture) can help identify molecular changes that may be difficult to observe when only a single embryo is present. We conclude that MET can be used for studying very early maternal-embryo interactions in vivo in monotocous species. Free Spanish abstract: A Spanish translation of this abstract is freely available at http://www.reproduction-online.org/content/150/2/ R35/suppl/DC1.Reproduction (2015) 150 R35-R43

Oviduct epithelium induces interferon-tau in bovine Day-4 embryos, which generates an anti-inflammatory response in immune cells

“…In our study, we used multiple embryos in order to amplify the signals from embryos, such that changes in gene expression in BOECs and also in PBMCs could be clearly detected. In fact, multiple embryos are known to develop normally in the oviduct and uterus of superovulated cattle until D7 of pregnancy 27 . Therefore, it is likely that the multiple embryos in our study did not elicit abnormal responses in BOECs and PBMCs gene expression.…”

The bovine embryo hatches from the zona pellucida through either the embryonic or abembryonic pole

“…In the cow, hatching takes place in the uterus [17] and it remains to be seen whether the endometrium responds differently to a blastocyst hatching from the embryonal vs abembryonal poles. This is a possibility because gene expression varies between ICM and TE [25] and recent experiments in cattle indicate that the cleavage-stage embryo can interact with the oviduct to change gene expression [26,27]. The cow is distinct from other species studied because abembryonal hatching predominates in the mouse [12], human [15], guinea pig [16], and hamster [28].…”

Blastocyst-induced changes in the bovine endometrial transcriptome

“…Several groups, including our own, have reported the use of multiple embryo transfer to study early embryo development and maternal communication (Clemente et al 2011, Ledgard et al 2012, Spencer et al 2013, O'Hara et al 2014, Gómez & Muñoz 2015. Through amplification, such an approach may facilitate the identification of molecular changes that would otherwise be difficult to observe under physiological conditions when a single embryo is present.…”