Members of the lysyl oxidase family are expressed during the development of the frog Xenopus laevis

Lysyl oxidase (Lox) is a copper-dependent amine oxidase that catalyzes the cross-linking of collagen and elastin fibers in the extracellular matrix (ECM). In mammals, four closely related Lox-like enzymes have been described that share a highly conserved catalytic domain with Lox. We have characterized Xenopus laevis cDNAs for Lox, Loxl-1, and Loxl-3, and show that they are expressed during early embryonic development. Using RT-PCR we detected maternal transcripts for Xloxl-1, but levels remained low until tailbud stages. Transcripts for Xlox and Xloxl-3 were not detected until early neurulae, although transcripts for Xlox remained at low levels until tailbud stages. Whole mount in situ hybridization showed that transcripts for Xloxl-1 and Xloxl-3 are localized in the notochord, while transcripts for Xlox are found in the notochord, somites, and head. X. laevis Lox-like enzymes were inhibited by incubating embryos, from cleavage stages to tadpole stages, in β-aminopropionitrile, a specific inhibitor of the catalytic domain. The resulting embryos appeared to differentiate normally but suffered from poor collagen fiber formation. Defects included kinks in the notochord, a posterior shift of the somites, abnormal gut coiling, and the formation of edemas. Our data suggest that Lox-related enzymes are required for the proper formation of the ECM during X. laevis development.