Abstract
BackgroundThe progression of implantation and placentation in ruminants is complex and is regulated by interplay between sex steroids and local signaling molecules, many of which have immune function. Chemokines and their receptors are pivotal factors in implantation and vascularization of the placenta. Based on known critical roles for chemokine receptor 4 (CXCR4) during early pregnancy in other species, we hypothesized that CXCR4 and its ligand CXCL12 would increase in the endometrium and conceptus in response to implantation in ewes. The objectives of the current study were to determine if CXCL12 and CXCR4 were upregulated in: endometrium from pregnant compared to non-pregnant ewes and in, conceptuses, cotyledons, caruncles and intercaruncular tissue.MethodsTissues were collected from sheep on Days 12, 13, 14, and 15 of either the estrous cycle or pregnancy and from pregnant ewes on Days 35 and 50. Blood samples from jugular and uterine vein were also collected on all days. Conceptuses were collected from mature ewes on Days 13, 15, 16, 17, 21 and 30 of gestation. Real time PCR was used to determine relative mRNA concentrations for CXCL12 and CXCR4 and Western blot analysis was employed to confirm protein concentration.ResultsDifferences described are P < 0.05. In the endometrium, CXCR4 mRNA and protein was greater on Day 15 of pregnancy compared to the estrous cycle. CXCL12 and CXCR4 mRNA in conceptuses was greater on Days 21 and 30 compared to earlier days. CXCL12 mRNA was greater in cotyledons on Day 35 compared to Day 50. On Day 35 of gestation, CXCR4 was greater compared to Day 50 in caruncle and intercaruncular tissue. White blood cells obtained from jugular and uterine vein collection had the greatest mRNA concentration of CXCL12 on Day 35 of pregnancy.ConclusionsA comprehensive analysis of CXCL12 and CXCR4 expression in fetal and maternal tissues during early pregnancy is reported with noteworthy differences occurring during implantation and placentation in sheep. We interpreted these data to mean that the CXCL12/CXCR4 pathway is activated during implantation and placentation in sheep and is likely playing a role in the communication between trophoblast cells and the maternal endometrium.
Highlights
The progression of implantation and placentation in ruminants is complex and is regulated by interplay between sex steroids and local signaling molecules, many of which have immune function
CXCR4 mRNA was greater (P < 0.05) in the endometrium from pregnant compared to non-pregnant ewes on Day 15 of gestation (Figure 1B)
CXCL12 mRNA was greater (P < 0.05) in cotyledons on Day 35 compared to Day 50 (Figure 4A), whereas CXCR4 did not differ in cotyledon tissue between these two gestational ages (Figure 4B)
Summary
The progression of implantation and placentation in ruminants is complex and is regulated by interplay between sex steroids and local signaling molecules, many of which have immune function Chemokines and their receptors are pivotal factors in implantation and vascularization of the placenta. A remarkable attribute of normal pregnancy is the delicate communication that exists between trophoblast cells and differentiated maternal cells in the uterus These cells communicate by an array of chemokines in a precise spatial and temporal pattern [8,9]. The progression of implantation and placentation in ruminants is a complex and prolonged process that is regulated by interplay between sex steroids and local signaling molecules, many of which have immune function CXCR4 is expressed in a multitude of tissues and cell types, including neutrophils, all B cells and monocytes, the majority of T-lymphocytes, endothelial cells, and epithelial cells [13] and its primary ligand is the stromal derived factor-1, known as CXCL12
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