Cloning and characterization of a cDNA coding for Astacus embryonic astacin, a member of the astacin family of metalloproteases from the crayfish Astacus astacus

The astacin family of zinc endopeptidases was named after the digestive enzyme astacin isolated from the crayfish Astacus astacus . Employing a reverse transcription/PCR strategy with degenerate oligonucleotide primers specific for two signature seqences of the astacin family, we have isolated a 1602‐bp cDNA from embryos of developing A. astacus eggs, which was designated Astacus embryonic astacin (AEA). This cDNA was found to code for an astacin‐like protease domain which accounts for the N‐terminal half of the predicted protein. The C‐terminal half mainly consists of two complement subcomponent C1r/C1s/embryonic sea urchin protein Uegf/bone morphogenetic protein 1 (CUB) domains. The metalloprotease domain displays an amino acid sequence identity of 42 % with astacin. A higher sequence similarity was found to astacin family members that act as hatching enzymes in different species, e.g. chorioallantoic membrane protein 1 (CAM‐1; from quail) and Xenopus hatching enzyme (formerly UVS.2), both of which show 54 % identity, and high and low choriolytic enzymes (HCE and LCE) from the teleost Oryzias latipes (52 % and 48 % identity, respectively). A relationship to astacin‐like hatching enzymes is further supported by a phylogenetic analysis of the protease domains. Expression of AEA mRNA in developing embryos was found to be restricted to unhatched juveniles (larvae) during the last 8 days before hatching. AEA transcripts could not be detected in various tissues of adult animals or in eggs and embryos from an earlier developmental stage. AEA expression starts about 8 days prior to hatching, followed by a strong (18‐fold) induction with a maximum at day 4 before hatching. Newly hatched juveniles were found not to express the AEA mRNA.