Unraveling the elongating bovine conceptus microenvironment: Identification of gene transcripts and proteins along the conceptus-maternal interface in cattle

The bovine conceptus elongates near Day 16 of development and releases interferon-tau (IFNT), disrupting the endometrial luteolytic mechanism to sustain luteal P4 and pregnancy. Conceptus factors other than IFNT modify local endometrial activities in support of pregnancy; however, the microenvironment is largely uncharacterized. We utilized a bovine conceptus-endometrial culture system to elucidate the microenvironment in the form of RNA 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 cyclic endometrium were then used to generate tissue cultures in 1 mL of medium: (1) no tissue (Control Med; n=7), (2) mono-cultured conceptus (Conceptus; n=9), (3) mono-cultured endometrium (Endo; n=13), or (4) Endo-Conceptus co-culture (n=15). After 12 h, tissue RNA was sequenced (RNA-Seq) and media underwent proteomic analysis (LC-MS/MS). Compared to Conceptus and Endo, co-cultured conceptus and endometrial tissue contained 3,400 and 4,575 differentially expressed genes (DEG), respectively (P ≤ 0.01). Upregulated endometrial DEG, independent of IFNT, were associated with transcription whereas upregulated conceptus DEG were associated with protein homeostasis and metabolism (P ≤ 0.001). All procedures involving animals were approved by the University of Tennessee, Knoxville, Institutional Animal Care and Use Committee (IACUC 2020-67015-31617). Estrus synchronized Angus-Holstein heifers were used to generate cyclic Day 16 endometrial explants or elongated Day 16 bovine conceptuses. Endometrial explants (8 mm) and conceptus sections (5 X 2 mm) were cultured in medium separately (monoculture) or together in a co-culture system. After a 12 h incubation, the endometrial and conceptus tissue RNA was also isolated for RNA sequencing (RNA-Seq). Collectively, 13 cyclic uteri and and 9 conceptuses were used to produce endometrial explants and conceptus sections for mono- and co-cultures.