DUAL GENETIC PATHWAYS OF ENDOTHELIN-MEDIATED INTERCELLULAR SIGNALING REVEALED BY TARGETED DISRUPTION OF ENDOTHELIN-CONVERTING ENZYME-1 GENE

Recent gene targeting studies have revealed unexpected roles for endot helins in the development of neural crest-derived tissues. Endothelin converting enzyme-1 (ECE-1) catalyzes the proteolytic activation of bi g endothelin-1 to endothelin-1(ET-1) in vitro. However, the importance of ECE-1 cleavage in the multiple endothelin pathways in vivo is unkn own. Here we generated a targeted null mutation in the mouse ECE-1 gen e. ECE-1(-/-) term embryos exhibited craniofacial and cardiac abnormal ities virtually identical to the defects seen in ET-1 and endothelin A receptor (ETA)-deficient embryos. Epidermal melanocytes as well as en teric neurons of the distal gut were also absent in ECE1(-/-) embryos, reproducing the developmental phenotype seen in ET-3(-/-) and endothe lin B receptor (ETB)(-/-) mice. Surprisingly, large amounts of mature ET-1 peptide are found in ECE-1(-/-) embryos, indicating that non-ECE- 1protease(s) can activate ET-1 at certain sites. However, these enzyme s cannot produce sufficient mature endothelin at the locations crucial for normal embryonic development. These findings reveal that ECE-1 is a bona fide activating protease for both big ET-1 and big ET-3 in viv o, and that the cell-cell communication pathways represented by the ET -1/ECE-1/ETA axis and the ET-3/ECE-1/ETB axis are each involved in the development of distinct subsets of neural crest cell lineages. Mutati ons in ECE-1 may cause developmental defects in humans, such as Hirsch sprung disease, velocardiofacial syndrome and related neurocristopathi es.