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.