New sources of retinoic acid synthesis revealed by live imaging of an Aldh1a2‐GFP reporter fusion protein throughout zebrafish development

Background: Regulation of synthesis and turnover of retinoic acid (RA) is an important mechanism that controls the activity of RA signaling during vertebrate development. During embryonic patterning, the dynamic expression patterns of the aldh1a2 gene, which encodes a retinaldehyde dehydrogenase, provide the major source of RA, whereas the only other retinaldehyde dehydrogenase in teleosts, aldh1a3, is expressed later and locally restricted. Aldh1a2-mediated RA synthesis has been shown to also regulate adult cell fates, such as during heart and fin regeneration. However, only very few other sites of postembryonic RA synthesis in vertebrates are known. We generated transgenic lines in zebrafish by BAC recombineering that express a fusion protein of Aldh1a2 and green fluorescent protein (GFP) under the control of endogenous aldh1a2 regulatory sequences (aldh1a2:gfp). Results: aldh1a2:gfp reports the complete endogenous expression pattern in embryos and rescues embryonic lethality in aldh1a2 mutants. We identify novel postembryonic sources of RA synthesis, including lateral line support cells, in kidney-derived organs that regulate calcium homeostasis, and in perichordal cells during vertebral development. Conclusions: The novel aldh1a2 reporter line is driven by the complete set of regulatory sequences required for zebrafish development, reports novel sources of RA synthesis, and identifies the source of RA that promotes vertebral ossification. Developmental Dynamics 241:1205–1216, 2012. © 2012 Wiley Periodicals, Inc.