Dynamic changes in gene expression and signalling during trophoblast development in the horse.

Equine chorionic girdle trophoblast cells play important endocrine and immune functions critical in supporting pregnancy. Very little is known about the genes and pathways that regulate chorionic girdle trophoblast development. Our aim was to identify genes and signalling pathways active in vivo in equine chorionic girdle trophoblast within a critical 7 days window. We exploited the late implantation of the equine conceptus to obtain trophoblast tissue. An Agilent equine 44K microarray was performed using RNA extracted from Chorionic Girdle and Chorion (control) from equine pregnancy days 27, 30, 31 and 34 (n=5), corresponding to the initiation of chorionic girdle trophoblast proliferation, differentiation and migration. Data was analysed using R packages limma and maSigPro, Ingenuity Pathway Analysis and DAVID and verified using qRT-PCR, promoter analysis, western blotting and migration assays. Microarray analysis showed gene expression (absolute log FC > 2, FDR-adjusted P<0.05) was rapidly and specifically induced in the chorionic girdle between days 27 and 34 (compared to day 27, day 30=116, day 31=317, day 34=781 genes). Pathway analysis identified 35 pathways modulated during chorionic girdle development (e.g. FGF, Integrin, Rho GTPases, MAPK) including pathways that have limited description in mammalian trophoblast (e.g. IL-9, CD40 and CD28 signalling). Rho A and ERK/MAPK activity was confirmed as was a role for transcription factor ELF5 in regulation of the CGB promoter. The purity and accessibility of chorionic girdle trophoblast proved to be a powerful resource to identify candidate genes and pathways involved in early equine placental development.