Novel equine conceptus-endometrial interactions on Day 16 of pregnancy based on RNA sequencing

Maintenance of pregnancy is dependent on the exchange of signals between the conceptus and the endometrium. The objective of this study was to use next-generation sequencing to determine transcriptome blueprints of the conceptus and endometrium 16 days after ovulation in the horse. There were 7760 and 10 182 genes expressed in the conceptus and endometrium, respectively, of which 7029 were present in both. Genes related to developmental processes were enriched among conceptus-specific transcripts, whereas many endometrium-specific genes had known roles in cell communication, cell adhesion and response to stimuli. The integrin signalling pathway was overrepresented in both transcriptomes. In that regard, it was hypothesised that integrins ITGA5B1 and ITGAVB3 interact with conceptus-derived fibrinogen, potentially contributing to cessation of conceptus mobility. That several growth factors and their corresponding receptors (e.g. HDGF, NOV, CYR61, CTGF, HBEGF) were expressed by conceptus and endometrium were attributed to cross-talk. In addition, Cytoscape interaction analysis revealed a plethora of interactions between genes expressed by the conceptus and endometrium, during a period when the former had substantial movement within the uterus. This is the first report of concurrent transcriptome analysis of conceptus and endometrium in the mare, with numerous findings to provide rationale for further investigation.