Markers of equine placental differentiation: insights from gene expression studies

Abstract

Development and the subsequent function of the fetal membranes of the equine placenta requires both complex and precise regulation of gene expression. Advancements in recent years in bioinformatic techniques have allowed more extensive analyses into gene expression than ever before. This review starts by combining publically available transcriptomic datasets obtained from a range of embryonic, placental and maternal tissues, with previous knowledge of equine placental development and physiology, to gain insights into key gene families relevant to placentation in the horse. Covering the whole of pregnancy, the review covers trophectoderm, yolk sac, chorionic girdle cells, allantoamnion, allantochorion. In particular, 182 predicted ‘early high impact’ genes were identified (>100 TPM and >100 fold-change) that distinguish between progenitor trophectoderm, chorionic girdle tissue and allantochorion. Furthermore, 77 genes were identified as enriched in placental tissues (placental TPM > 10, with minimal expression in 12 non-placental < 1 TPM), including excellent candidates for functional studies such as IGF1, apolipoproteins, VGLL1, GCM1, CDX2 and FABP4. One gene with a currently unknown function was only identified (miR-675) in chorionic girdle but no other placental or adult tissues. It is pertinent that future studies focus on single cell transcriptomic approaches in order to determine how these changes in gene expression relate to tissue composition and start to better define trophoblast subpopulations in the equine placenta. Future functional characterisation of these genes and pathways will also be key not only to understanding normal placental development and fetal health but also their potential role in pathologies of pregnancy.

Pregnancy monitoring in mares: Ultrasonographic and endocrine approaches

“…As noted earlier, fetal tissues have considerable capacity for oestrogen synthesis, and equine endometrium is very active in sulphation (Heap et al, 1982). Chorio‐allantoic steroidogenic enzyme expression at day 45 of gestation is also consistent with the synthesis of estrone sulphate (Loux et al, 2020), and there were strong positive correlations between chorio‐allantoic expression of CYP17A and CYP19A with maternal serum dehydroepiandrosterone (DHEA) and estrone sulphate, respectively, in maternal blood (Loux et al, 2022). This suggests that eCG stimulation of luteal androgen secretion (Albrecht et al, 1997; Daels et al, 1998; Daels et al, 1996; Legacki et al, 2016a, 2016b) may provide substrate for aromatization in the chorio‐allantois and sulphation in the fetal membranes or endometrium (Heap et al, 1982, 1991; Loux et al, 2020) as illustrated (Figure 3b).…”