what seems like a counter-intuitive move against survival, within animals, some cells are fated to die from the triggering of an elaborate cell death program, known as apoptosis. Now, Sakamaki et. al., have honed in on understanding the evolution of caspase-8, a key cell death initiator molecule that was first identified in humans.
By performing the most extensive evolutionary analysis of the Casp8 protein to date, they found that Casp8 activity arose very early (more than 500 MYA), and is universally conserved throughout evolution, demonstrating its functional significance throughout the animal kingdom.
Thus, the cell death toolkit is of core importance to animal evolution, with cell death occurring to eliminate unnecessary, non-functional, unhealthy, or dangerous cells from the body. “In mammals, the cells producing a death ligand and expressing death receptor (and FADD/casp8) are different, suggesting that cell-cell communication is required for this vital phenomenon,” said Sakamaki.
Sounds like neither a bug nor a feature but a benefit. Thoughts?
Here’s the abstract:
The caspases, a family of cysteine proteases, play multiple roles in apoptosis, inflammation, and cellular differentiation. Caspase-8 (Casp8), which was first identified in humans, functions as an initiator caspase in the apoptotic signaling mediated by cell-surface death receptors. To understand the evolution of function in the Casp8 protein family, casp8 orthologs were identified from a comprehensive range of vertebrates and invertebrates, including sponges and cnidarians, and characterized at both the gene and protein levels. Some introns have been conserved from cnidarians to mammals, but both losses and gains have also occurred; a new intron arose during teleost evolution, whereas in the ascidian Ciona intestinalis, the casp8 gene is intronless and is organized in an operon with a neighboring gene. Casp8 activities are near ubiquitous throughout the animal kingdom. Exogenous expression of a representative range of nonmammalian Casp8 proteins in cultured mammalian cells induced cell death, implying that these proteins possess proapoptotic activity. The cnidarian Casp8 proteins differ considerably from their bilaterian counterparts in terms of amino acid residues in the catalytic pocket, but display the same substrate specificity as human CASP8, highlighting the complexity of spatial structural interactions involved in enzymatic activity. Finally, it was confirmed that the interaction with an adaptor molecule, Fas-associated death domain protein, is also evolutionarily ancient. Thus, despite structural diversity and cooption to a variety of new functions, the ancient origins and near ubiquitous distribution of this activity across the animal kingdom emphasize the importance and utility of Casp8 as a central component of the metazoan molecular toolkit.
Follow UD News at Twitter!