This study aimed to characterize the endometrial transcriptome and functional pathways overrepresented in the endometrium of cows treated to ovulate larger (≥ 13 mm) versus smaller (≤ 12 mm) follicles. Nelore cows were pre-synchronized prior to receiving cloprostenol (large follicle; LF) or not (small follicle group; SF), along with a progesterone device on D−10. Devices were withdrawn and cloprostenol administered 42 to 60 hours (LF) or 30 to 36 hours (SF) before GnRH agonist treatment (D0). Tissues were collected on D4 (Exp.1; N = 24) or D7 (Exp.2; N = 60). Endometrial transcriptome was obtained by RNA-seq whereas proliferation and apoptosis were assessed by immunohistochemistry. Overall, LF cows developed larger follicles and CLs, and produced greater amounts of E2 (D-1; Exp.1; SF: 0.7±0.2; LF: 2.4±0.2 pg/mL; Exp.2; SF: 0.5±0.1; LF: 2.3±0.6 pg/mL) and P4 (D4; Exp.1; SF: 0.8±0.1; LF: 1.4±0.2 ng/mL; D7; Exp.2; SF: 2.5±0.4; LF: 3.7±0.4 ng/mL). Functional enrichment indicated that biosynthetic and metabolic processes were enriched in LF endometrium, whereas SF endometrium transcriptome was biased towards cell proliferation. Data also suggested reorganization of the extracellular matrix (ECM) towards a proliferation permissive phenotype in SF endometrium. LF endometrium showed an earlier onset of proliferative activity, whereas SF endometrium expressed a delayed increase in glandular epithelium proliferation. In conclusion, the periovulatory endocrine milieu regulates bovine endometrial transcriptome and seems to determine the transition from a proliferation permissive to a biosynthetic and metabolically active endometrial phenotype, which may be associated with the preparation of an optimally receptive uterine environment.

In cattle, the oviduct is a tubular organ that connects the ovary and the uterus. The oviduct lumen stages a dynamic set of cellular and molecular interactions to fulfill the noble role of generating a new individual. Specific anatomical niches along the oviduct lumen provide the appropriate microenvironment for final sperm capacitation, oocyte capture and fertilization, and early embryo development and transport. To accomplish such complex tasks, the oviduct undergoes spatially and temporally-regulated morphological, biochemical, and physiological changes that are associated with endocrine events of the estrous cycle. Specifically, elevated periovulatory concentrations of estradiol (E2) and progesterone (P4) influence gene expression and morphological changes that have been associated positively to fertility in beef cattle. In this review, we explore how E2 and P4 influence oviductal function in the beginning of the estrous cycle, and prepare the oviductal lumen for interactions with gametes and embryos.

A major, unresolved issue is how the uterine microenvironment determines pregnancy success in cattle. Before implantation, conceptus development depends on the uterine secretome (i.e., histotroph). Despite its pivotal role, little is known about the dynamics of histotroph synthesis and changes in composition throughout the early diestrus and the relevance to pregnancy establishment. We hypothesize that disturbances on histotroph composition affect the establishment of pregnancy. Aim was to disturb histotroph composition at early diestrus and verify the effects on: (Exp. 1) timing to restore its composition; and (Exp. 2) pregnancy rate after multiple-embryo transfer. Estrous cycle of multiparous Nelore cows were synchronized and estrus was considered d 0 (D0) of the experiments. Disturbance was through flushing each uterine horn with 30 mL of DMPBS and collecting the resulting uterine luminal flushing (ULF) on D1; D4; D7; D1 + D4 + D7. Control group remained not-collected. In Exp. 1, ULF was collected on D7.5 from all animals and used for quantification of total protein concentration and abundance of albumin. In Exp. 2, three in vitro-produced embryos were transferred to the uterine horn ipsilateral to the ovary containing the CL on D7.5 and pregnancy was checked on D25 by ultrasound. In Exp. 1, ULF collection on D4 or D7 increased (1.5- to 2.2-folds) the total protein concentration and albumin abundance. ULF collection on D1 did not alter (P > 0.10) these endpoints. In Exp. 2, ULF collected on D4 or D7 decreased pregnancy rates to approximately half of that measured in the remaining groups. Subtle perturbations imposed to the native intrauterine milieu, such as those caused by a single, low-volume collection of ULF, profoundly disturbs intrauterine composition and pregnancy success. At least 4 d were necessary for the uterus to recover its composition and the functional capacity to carry post-implantation gestation.

The extracellular matrix (ECM) is a group of molecules that offer structural and biochemical support to cells and interact with them to regulate their function. Also, growth factors (GFs) stored in the ECM can be locally released during ECM remodeling. Here, we hypothesize that the balance between ECM components and remodelers is regulated according to the ovarian steroid milieu to which the oviduct is exposed during the periovulatory period. Follicular growth was manipulated to generate cows that ovulated small follicles (SF-small corpus luteum [SCL]; n = 20) or large follicles (LF-large corpus luteum [LCL]; n = 21) and possess corresponding Estradiol (E2) and Progesterone (P4) plasmatic concentrations. Ampulla and isthmus samples were collected on day 4 (day 0 = ovulation induction) and immediately frozen or fixed. The transcriptional profile (n = 3/group) was evaluated by RNA sequencing. MMP Antibody Array was used to quantify ECM remodelers’ protein abundance and immunohistochemistry to quantify type I collagen. Transcriptome analysis revealed the over-representation of ECM organization and remodeling pathways in the LF-LCL group. Transcription of ECM components (collagens), remodelers (ADAMs and MMPs), and related GFs were upregulated in LF-LCL. Protein intensities for MMP3, MMP8, MMP9, MMP13, and TIMP4 were greater for the LF-LCL group. Type I collagen content in the mucosa was greater in SF-SCL group. In conclusion, that the earlier and more intense exposure to E2 and P4 during the periovulatory period in LF-LCL animals stimulates ECM remodeling. We speculate that differential ECM regulation may contribute to oviductal receptivity to the embryo.

Information on molecular mechanisms through which sex-steroids regulate oviductal function to support early embryo development is lacking. Here, we hypothesized that the periovulatory endocrine milieu affects the miRNA processing machinery and miRNA expression in bovine oviductal tissues. Growth of the preovulatory follicle was controlled to obtain cows that ovulated a small follicle (SF) and subsequently bore a small corpus luteum (CL; SF-SCL) or a large follicle (LF) and large CL (LF-LCL). These groups differed in the periovulatory plasmatic sex-steroid’s concentrations. Ampulla and isthmus samples were collected on day four of the estrous cycle. Abundance of DROSHA, DICER1, and AGO4 transcripts was greater in the ampulla than the isthmus. In the ampulla, transcription of these genes was greater for the SF-SCL group, while the opposite was observed in the isthmus. The expression of the 88 most abundant miRNAs and 14 miRNAs in the ampulla and 34 miRNAs in isthmus were differentially expressed between LF-LCL and SF-SCL groups. Integration of transcriptomic and miRNA data and molecular pathways enrichment showed that important pathways were inhibited in the SF-SCL group due to miRNA control. In conclusion, the endocrine milieu affects the miRNA expression in the bovine oviduct in a region-specific manner.