Structure and spatio temporal expression of the full length DNA complementary to RNA coding for alpha2 type I...

Twenty distinct genetic types of collagen have been identified up to now. Their structure and function are not completely elucidated. We have chosen zebrafish as a model to bring information about the role of collagen during embryogenesis. In the present study, we isolated four overlapping DNA complementary to RNA clones covering the 4879 nucleotides of a zebrafish messenger RNA (mRNA) encoding a fibrillar procollagen chain. The comparison of its primary structure with known other vertebrate collagens allowed to conclude that it encodes collagen pro-alpha2(I) chain. The 5' untranslated region showed a typical stem-loop structure with three ATG codons which is found in mammals types I and III collagen chains (but not in type II), which are expressed in the same tissues. This suggests that the supposed regulatory role of the stem loop structure could be tissue specific. The comparison of the Gly-Gly doublets found along the helical domain of several species allowed to speculate that the Gly-Gly repeats could be a poikilotherm feature. Expression of pro-alpha2(I) was examined during zebrafish development by reverse transcriptase-polymerase chain reaction and in situ hybridization on whole embryo and tissue section. Col1a2 was expressed as early as stage10 h post fertilization (hpf) and two peaks of expression were observed at 20 and 48 hpf. alpha2 mRNAs, whose presence suggests a collagen synthesis, were detected principally in the superficial cell layers surrounding 20-72 hpf embryos which are characterized by an acellular collagen stratum. At 26-30 days, fibroblasts invade the dermis and take over from the epithelial cells to synthesize collagen. This suggests a fine regulation of collagen synthesis in these cells that remains to be elucidated. alpha2 mRNA were also detected in other tissues such as the tail fin primordium and the notochord primordium suggesting a participation of type I collagen in a pathway for notochord and tail formation.