Evolution of viviparity and uterine angiogenesis: vascular endothelial growth factor (VEGF) in oviparous and viviparous skinks

Abstract

During pregnancy, uterine vasculature of live-bearing lizards proliferates to support embryonic growth and development. Vascular endothelial growth factor (VEGF) is the most potent of a suite of growth factors responsible for uterine vascularization in mammals. We have sequenced VEGF mRNA transcripts expressed in the uterus of oviparous and viviparous Australian skinks, and compared uterine VEGF expression in nonreproductive and late-reproductive Saiphos equalis, a fossorial viviparous skink. VEGF sequences differed between phylogenetic groups of skinks, rather than oviparous and viviparous skinks. Two transcripts were identified in the uterus of each species that had the same splice sites as human VEGF(165) and VEGF(189). A third transcript, found only in uterine and testis tissue from S. equalis, had the same splice sites as human VEGF(111). This is the first natural expression of VEGF(111), previously found only in human cultured cells subjected to environmental stress. All the three VEGF transcripts identified showed higher expression in uterus from late-reproductive S. equalis than nonreproductive females. The different angiogenic properties of VEGF transcripts provide a mechanism that may produce the variety of placental complexities observed in viviparous skinks. The presence of VEGF(111) in S. equalis may be an opportunity to investigate the function of this unique transcript in a whole animal system.