Matthew E. Wilson

Relationship between placental vascular endothelial growth factor expression and placental/endometrial vascularity in the pig.

Abstract We investigated the temporal association between placental vascular endothelial growth factor (VEGF), a potent stimulator of angiogenesis and vascular permeability, and changes in placental/endometrial vascularity on selected days throughout gestation in the pig. Placental and endometrial tissues were collected from sows on Days 25 (n = 4), 36 (n =6), 44 (n =6), 70 (n =5), 90 (n =5), and 112 (n =7) of gestation. Cross sections of the placental/endometrial interface of each conceptus were used to estimate the number of blood vessels per unit area via image analysis and the intensity of VEGF staining via immunohistochemistry. Placental tissues were also collected on these days to evaluate VEGF mRNA expression. Placental VEGF mRNA expression and the numbers of blood vessels per unit area of placental and adjacent endometrial tissue were low and decreasing from Day 25 to Day 44, before increasing (P < 0.05) markedly and progressively through Day 112. These data are consistent with the marked increase in VEGF immunostaining in the chorionic and uterine luminal epithelium from early to late gestation. Further, these increases in placental VEGF mRNA were positively correlated with fetal weight (r = 0.73; P < 0.0001) and placental efficiency (fetal weight/placental weight ratio; r = 0.66, P < 0.0001). These data are consistent with a role for VEGF in increasing the number of blood vessels at the placental endometrial interface, resulting in an increased capacity for nutrient transfer from the maternal to the fetal compartment.

Differential expression of cyclooxygenase-2 around the time of elongation in the pig conceptus.

Alterations in uterine luminal fluid composition as a result of conceptus estradiol-17beta production are believed to play a significant role in the loss of 30-40% of potential pig conceptuses. Shortly after the initiation of conceptus estradiol-17beta synthesis and secretion, the conceptuses are transformed from 1cm spheres to 2-5cm tubular forms and finally to filamentous threads of variable length via a process known as elongation. We have attempted to characterize gene products whose expression is either initiated or terminated as the conceptus elongates. Using RNA fingerprinting, we determined that the inducible form of the rate-limiting enzyme in prostaglandin synthesis, cyclooxygenase-2, is expressed in the filamentous pig conceptus, but not in either the spherical or transitional morphologies. Furthermore, increased expression of cyclooxygenase-2 by the filamentous conceptus was associated with increases in the content of prostaglandins (particularly prostaglandin E(2)) found in uterine luminal fluid.

Differential gene expression during elongation in the preimplantation pig embryo.

Summary: On day 12–13 of gestation, the preimplantation pig conceptus undergoes a dramatic morphologic change from an approximately 1‐cm sphere to a nearly 1‐m long thread. This transformation, referred to as elongation, occurs in just 12–24 h. Elongation is primarily the result of trophectodermal cell shape changes, as there is relatively little mitosis during this stage of development. Thus far, descriptions of elongation have been limited to histologic and immunofluorescent studies of cell morphology and gross biochemical evaluations. We hypothesized that the changes in trophectoderm morphology likely involves significant changes in gene expression. Therefore, we used RNA arbitrarily primed‐PCR (RAP‐PCR) to characterize potential differential gene expression by trophectodermal cells during pig conceptus elongation. We found that the porcine heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1 was shown to be differentially expressed by trophectodermal cells during elongation. We suggest that regulated alternative splicing may contribute to the morphogenetic process of elongation. genesis 26:9–14, 2000. Published 2000 Wiley‐Liss, Inc.