Hydra metalloproteinase 1: A secreted astacin metalloproteinase whose apical axis expression is differentially regulated during head regeneration

The newly emerging astacin metalloproteinase family comprises multiple memb ers with diverse functions. Most recently, the development-related function s have been attributed to both (1) proteolytic cleavage and subsequent rele ase of active TGF-beta-like growth factors from latent inhibitory complexes and (2) modification of extracellular matrix (ECM) assembly and compositio n. We previously identified and purified hydra metalloproteinase 1 (HMP-1), a developmentally important astacin proteinase that functions in head rege neration and transdifferentiation of tentacle battery cells (L. Yan ef al., 1995, Development 121, 1591-1602). In the present study, further cloning r evealed that HMP-1 is produced as a secreted zymogen with a conserved hydro phobic signal sequence and a putative propeptide. The processed HMP-1 is co mposed of a characteristic astacin proteinase domain and a unique Cys-rich C-terminus. With this simple domain structure, HMP-1 represents an ancestra l astacin proteinase. Consistent with its role in head regeneration, HMP-1 mRNA is expressed at highest levels by endodermal cells at the apical pole of the body column just inferior to the base of tentacles, the region of ac tive cell differentiation or transdifferentiation. A modified immunocytoche mical procedure demonstrated that HMP-1 protein can be localized not only t o ECM of tentacles as we previously reported, but also to endodermal cells of the body column in a pattern similar to its mRNA distribution. The local ization of HMP-1 protein in tentacles was confirmed using an enzymatic appr oach. A translocation of HMP-1 protein from cells in the body column to the extracellular milieu in tentacles further suggests that HMP-1 is a secrete d protein. HMP-1 expression undergoes extensive regulation at the transcrip tional level both temporally and spatially during head regeneration. The in volvement of HMP-1 in this morphogenetic process is further supported by th e blockage of head regeneration with localized antisense treatment. Taken t ogether, these results suggest that HMP-1 is a secreted astacin metalloprot einase that has an important role in regulating hydra head morphogenesis po tentially through its differential expression along the body axis. (C) 2000 Academic Press.