Hydrops Fetalis, Cardiovascular Defects, and Embryonic Lethality in Mice Lacking the Calcitonin Receptor-Like Receptor Gene

Abstract

Adrenomedullin (AM) is a multifunctional peptide vasodilator that is essential for life. To date, numerous in vitro studies have suggested that AM can mediate its biological effects through at least three different receptors. To determine the in vivo importance of the most likely candidate receptor, calcitonin receptor-like receptor, a gene-targeted knockout model of the gene was generated. Mice heterozygous for the targeted Calcrl allele appear normal, survive to adulthood, and reproduce. However, heterozygote matings fail to produce viable Calcrl ^−/− pups, demonstrating that Calcrl is essential for survival. Timed matings confirmed that Calcrl ^−/− embryos die between embryonic day 13.5 (E13.5) and E14.5 of gestation. The Calcrl ^−/− embryos exhibit extreme hydrops fetalis and cardiovascular defects, including thin vascular smooth muscle walls and small, disorganized hearts remarkably similar to the previously characterized AM ^−/− phenotype. In vivo assays of cellular proliferation and apoptosis in the hearts and vasculature of Calcrl ^−/− and AM ^−/− embryos support the concept that AM signaling is a crucial mediator of cardiovascular development. The Calcrl gene targeted mice provide the first in vivo genetic evidence that CLR functions as an AM receptor during embryonic development.

This work was supported by the Burroughs Wellcome Fund and The University of North Carolina School of Medicine grants to K.M.C., a training grant from the National Institutes of Health to R.T.D. (5-T32-GM007092-29), and a grant from the National Institutes of Health to O.S. (HL49277).

We thank Sylvia Hiller, Gleb Rozanov, Kirk McNaughton, and Kui Kwon Kim for technical assistance and Frank Conlon and Da-Zhi Wang for helpful advice and discussions.