EphrinB2 mRNA expression during chick mesonephros development and degeneration

Abstract

The cellular and molecular mechanisms underlying vasculogenesis and angiogenesis are still poorly understood. However, an increasing number of intercellular signaling molecules have been identified that play an essential role in this process. Prominent among these are transmembrane receptor tyrosine kinases and their ligands (angiopoietins, platelet-derived growth factors, vascular endothelial growth factors and ephrins). Moreover, it is known that repulsive signaling between arteries and veins is decisive for angiogenic remodeling during the functional maturation of the vascular system. Recently, ephrinB2 has been shown to be required for the remodeling of the embryonic blood vessels. Because of its exclusive expression on arteries and the complementary expression of one of its cognate receptors, EphB4, on veins, it was suggested that ephrinB2 acts both as a ligand and as a receptor for EphB4. However, it is not known the role of ephrinB2 during the tremendous vascular remodeling that occurs when an embryonic organ is functionally substituted by the definitive one. Avian mesonephros is an embryonic transitory organ with a complex, but well known, vascular system. Degeneration of the mesonephros leads to vessel disintegration. However, mesonephric vessels that communicate with metanephros, the definitive kidney, and gonads do not degenerate. The aim of this study is to analyze ephrinB2 mRNA expression throughout the development and degeneration of chick mesonephros, in order to understand the function of ephrinB2 during vascular mesonephric remodelation. In 24 HH embryos, ephrinB2 transcripts were observed in endothelial cells of dorsal aorta, vitelline, femoral, umbilical and intersomitic arteries. Mesonephric arteries with the ephrinB2 signal were only seen in the cranial part of the mesonephros. At stage 30, ephrinB2 mRNA was only observed in the dorsal aorta and the caudal mesonephric arteries. In 38 HH embryos, ephrinB2 expression was only present in the aorta and mesonephric arteries that will not degenerate. We found no ephrinB2 transcripts in glomerular capillaries or veins at any stage. In conclusion, the ephrinB2 temporal expression pattern matches the cranial-to-caudal morphogenetic gradient of mesonephros development. Totally differentiated mesonephric arteries do not express ephrinB2 and, when mesonephric degeneration occurs, only mesonephric arteries that remain expressed ephrinB2. Our results confirm the morphogenetic role of ephrinB2. Only arteries under remodelation expressed ephrinB2.