Purification and characterization of zebrafish hatching enzyme – an evolutionary aspect of the mechanism of egg envelope digestion

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This research investigates the hatching enzyme of zebrafish (Danio rerio), focusing on its purification, characterization, and the evolutionary implications of egg envelope digestion mechanisms. The study identified two hatching enzyme homologues in zebrafish, ZHE1 and ZHE2. Analysis revealed that ZHE1 is predominantly expressed and is the primary enzyme responsible for hatching, while ZHE2 expression is minimal. The research involved purifying ZHE1 from zebrafish hatching liquid, characterizing its enzymatic activity and substrate specificity. Comparisons were made with medaka hatching enzymes (MHCE and MLCE) and their respective egg envelopes to explore the evolutionary divergence of hatching mechanisms. The findings suggest that ZHE1 and MHCE likely retain characteristics of an ancestral hatching enzyme, potentially undergoing gene duplication and diversification to form enzymes like MLCE, which may have acquired new functions. The study also examines the cleavage sites of ZHE1 on both unfertilized and fertilized zebrafish egg envelopes, highlighting the role of ZHE1 in swelling and initiating the digestion of the egg envelope, which is crucial for embryo hatching.

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