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DIFFERENTIAL REGULATION OF VASCULAR ENDOTHELIAL GROWTH FACTOR EXPRESSION IN THE MARSUPIAL UTERUS.
Parry, Laura1,2, 1 2
ABSTRACT- In mammals, successful implantation and placentation involve expansion and differentiation of the uterine endometrial vascular bed, processes thought to involve the angiogenic peptide vascular endothelial growth factor (VEGF). Female marsupials have anatomically separate uteri and in monovular species such as the tammar, only one uterus is gravid with a single fetus whereas the contralateral uterus remains nongravid. This unique animal model enables us to identify systemic from fetal-specific factors in the regulation of uterine function. Tammars have a diffuse, epithelio-chorial placenta which forms when the shell membrane ruptures and the yolk sac interdigitates with the endometrial epithelium on Day 19 of the 26-day gestation. There is also a proliferation of the vasculature in the endometrial epithelium of the gravid uterus, which is directly influenced by the feto-placental unit. The aim of this study was to measure VEGF mRNA and protein levels in the endometrium of both uteri in pregnant tammar wallabies to determine if the conceptus itself influences endometrial vascularization via expression of VEGF. Real Time PCR was used to quantify VEGF mRNA levels and immunohistochemistry techniques assessed immunoreactive VEGF. The nucleotide and derived amino acid sequences of the tammar VEGF cDNA molecule were first obtained using PCR strategies and RNA from the gravid endometrium. Two PCR clones of 495 and 550 bp were sequenced and shown to encode the amino acid variants VEGF165 and VEGF189, with 75-82% homology at the amino acid level compared with human, rat and sheep VEGF cDNAs. VEGF165 appears to be the predominant isoform in the tammar endometrium and its expression is significantly (P<0.05: ANOVA) upregulated only in the gravid uterus between Days 20 and 23 of gestation. Immunoreactive VEGF is detected in the endometrial epithelium of the gravid uterus but is absent in the nongravid uterus. In abnormal pregnancies in which the gravid uterus was distended but lacked a fetus or vascular placenta, no VEGF transcripts or protein were detected in the gravid endometrium. These data show that the feto-placental unit is involved in the regulation of VEGF synthesis in the tammar endometrium and that vascularization in the gravid uterus may be induced by an increase in VEGF.
KEY WORDS: VEGF, endometrium, marsupial