Expression and characterization of the "laminin binding protein" in hydra

Recently, a cDNA was isolated from hydra with extensive homology to a mammalian and invertebrate gene which codes for a protein called laminin binding protein (LBP). In this paper we describe the protein expression of the hydra LBP in Escherichia coli. On SDS gels the recombinant hydra LBP displayed an apparent molecular mass of 43 kDa, although the calculated mass, including six additional histidines, is 33.7 kDa. Polyclonal antibodies were produced against the hydra recombinant LBP. The antiserum reacted with a 42-kDa and a 43-kDa protein from Hydra vulgaris and from a multiheaded mutant of Chlorohydra viridissima, respectively. In hydra, LBP RNA and protein were highly expressed in cells with short cell cycles, such as all cells of the interstitial cell lineage, less in slowly cycling epithelial cells, and at very reduced levels or not at all in differentiated cells. Higher expression in the multiheaded mutant of C. viridissima than in H. vulgaris, the cells of which differ in doubling time, hint at a function in cell proliferation. This is supported by the finding that in vitro hydra LBP is a substrate for the cell-cycle-specific kinase CDC2.