The Protease Degrading Sperm Histones Post-Fertilization in Sea Urchin Eggs Is a Nuclear Cathepsin L That Is Further Required for Embryo Development

Proteolysis of sperm histones in the sea urchin male pronucleusis the consequence of the activation at fertilization of a maternal cysteine protease. We previously showed that this protein is required for male chromatin remodellingand for cell-cycle progression in the newly formed embryos. This enzyme is present in the nucleus of unfertilized eggs and is rapidly recruited to the male pronucleusafter insemination. Interestingly, this cysteine-proteaseremains co-localized with chromatin during S phase of the first cell cycle, migrates to the mitotic spindle in M-phase and is re-located to the nuclei of daughter cells after cytokinesis. Here we identified the protease encoding cDNA and found a high sequence identity to cathepsinproteases of various organisms. A phylogenetical analysis clearly demonstrates that this sperm histone protease (SpHp) belongs to the cathepsin Lsub-type. After an initial phase of ubiquitous expression throughout cleavage stages, SpHp gene transcripts become restricted to endomesodermic territories during the blastulastage. The transcripts are localized in the invaginating endodermduring gastrulationand a gut specific pattern continues through the prism and early pluteusstages. In addition, a concomitant expression of SpHp transcripts is detected in cells of the skeletogenic lineage and in accordance a pharmacological disruption of SpHp activity prevents growth of skeletal rods. These results further document the role of this nuclear cathepsin Lduring development.