Regionally and hormonally regulated expression of genes of collagen and collagenase in the anuran larval skin.

The skin of an anuran tadpole undergoes region-dependent metamorphic changes: the body (head and body trunk) transforms into the adult type, while the tail falls into programmed cell death. The present study was undertaken to investigate the regional specificity of metamorphosis at a molecular level, focusing on genes of collagen and collagenase that are known to be activated in their synthesis at metamorphosis. A cDNA probe utilized for collagen was Hf677 (a clone of human type I collagen alpha 1 chain). A probe for collagenase gene was cloned in the present study from a cDNA library of bullfrog tadpole skin, characterized and named Tc1. Tc1 contained the consensus sequence of zinc-metalloproteinases and showed a high homology to mammalian collagenases. Using these recombinant DNAs as probes, RNA blot analyses were performed for the body and tail skin of tadpoles that had been in spontaneous metamorphosis, induced to metamorphosis by the injection of thyroid hormone, or had been induced to grow by prolactin treatment. Collagenase gene was activated irrespective of regions of the skin, body or tail at the early metamorphic climax stage, although the extent of activation was region-dependent. In contrast, metamorphic changes of collagen gene expression showed a clear regional dependency. The transcription level in body skin was enhanced at the onset of metamorphosis while that in tail skin was markedly suppressed. Thyroid hormone was shown to be responsible for this region-dependent expression of collagen genes at metamorphosis. Prolactin, a suppressor hormone of amphibian metamorphosis, enhanced the transcription of collagen genes and suppressed that of collagenase.(ABSTRACT TRUNCATED AT 250 WORDS)