Molecular cloning and expression of a novel CYP26 gene (cyp26d1) during zebrafish early development

Proper restriction of retinoid signaling by Cyp26s is essential for development of vertebrate embryos while inappropriate retinoid signaling can cause teratogenesis. Here, we report cloning and expression analysis of a novel cyp26 gene (cyp26d1) isolated from zebrafish. The predicted protein encoded by cyp26d1 consists of 554 amino acids. It exhibits 54% amino acid identity with human Cyp26C1, 50% with zebrafish Cyp26B1 and 38% with zebrafish Cyp26A1. Whole-mount in situ hybridization shows that cyp26d1 is first expressed in sphere stage, then disappears at 50% epiboly and resumes its expression at 75% epiboly. During segmentation period, cyp26d1 message is found at presumptive hindbrain. Double in situ hybridization with krox20 and cyp26d1 reveals that cyp26d1 is expressed in presumptive rhombomere 2-4 (r2-r4) at 2-somite stage. At 3-somite stage, cyp26d1 gene is expressed in r6 and pharyngeal arch (pa) one in addition to its expression at r2 and r4. At 6-somite stage, cyp26d1 message is present in continuous bands at r2-r6 and in pa1. This expression pattern is maintained from 10-somite stage through 21-somite stage except that the expression level is greatly reduced at r2 and r4. At 21-somite stage, cyp26d1 is also found in a group of cells in telencephalon and diencephalons. At 25-31 h post-fertilization (hpf), the zebrafish cyp26d1 expression domain is extended to eyes, otic vesicles and midbrain in addition to its expression in hindbrain, telencephalon, diencephalons, and pharyngeal arches. At 35-48 hpf, the expression of cyp26d1 is mainly restricted to otic vesicles, pharyngeal arches and pectoral fins and the expression level is greatly reduced.