Unraveling the elongating bovine conceptus microenvironment: identification of gene transcripts and proteins along...

The bovine conceptus elongates near Day 16 of development and releases interferon-tau, disrupting the endometrial luteolytic mechanism to sustain luteal P4 and pregnancy. Conceptus factors other than interferon tau modify local endometrial activities to support pregnancy; however, the microenvironment is largely uncharacterized. We utilized a bovine conceptus-endometrial culture system to elucidate the microenvironment in the form of gene transcripts and protein. Estrus synchronized heifers remained cyclic (13) or were inseminated (9) to produce Day 16 cyclic endometrium and elongating conceptuses, respectively. Conceptus sections and endometrium were then used to generate tissue cultures in 1 ml of medium: (i) no tissue (control med; n = 7), (ii) mono-cultured conceptus (conceptus; n = 9) (iii) mono-cultured endometrium (endo; n = 13), or (iv) endo-conceptus co-culture (n = 15). After 12 h, tissue gene transcripts were sequenced (RNA-Seq) and media underwent proteomic analysis (LC-MS/MS). Compared to conceptus and endo, co-cultured conceptus and endometrial tissue contained 3400 and 4575 differentially expressed genes, respectively (P ≤ 0.01). More abundantly expressed endometrial differentially expressed genes were associated with interferon signaling whereas more abundantly expressed conceptus differentially expressed genes were associated with protein homeostasis and metabolism (FDR < 0.001). When co-culture media where compared to endo media, 288 more abundant proteins were identified (P < 0.05). Biological processes related to these proteins included antigen presentation via MHC Class Ib and keratinization (FDR < 0.001). Within the mono-cultured conceptus and endometrial media, folate receptor alpha (FOLR1; P < 0.001) was identified as the most abundant secreted protein suggesting the reproductive tissues elicit a microenvironment supportive of conceptus growth involving folate metabolism.