A retinoic acid-inducible modular protease in budding ascidians

Retinoic acid-treated mesenchyme cells of the budding ascidian Polyandrocar pa misakiensis acquire an organizer activity to induce a secondary body axi s when implanted into developing buds. We identified several different mRNA s that were upregulated in the mesenchyme cells after retinoic acid treatme nt. We isolated a cDNA clone corresponding to one of these mRNAs. The C-ter minal region of the predicted protein product is homologous to the catalyti c domain of serine proteases that belong to the trypsin family. The N-termi nal region contains several types of protein-protein interaction domains. W e therefore named this protein tunicate retinoic acid-inducible modular pro tease (TRAMP). Expression of the TRAMP mRNA in mesenchyme cells during budd ing and its upregulation by retinoic acid were demonstrated by reverse tran scription-PCR and in situ hybridization. A glutathione S-transferase-TRAMP fusion protein showed a protease activity with trypsin-like substrate speci ficity and stimulated proliferation of the cell line established in this sp ecies. (C) 1999 Academic Press.