Christophorou, M. A. | bioRxiv Science

bioRxiv2021

Peptidylarginine deiminase IV (PADI4) is not essential for cell-autonomous HSC maintenance and normal haematopoiesis

Peptidylarginine deiminases (PADIs, or PADs) are emerging as key regulators of human physiology and pathophysiology. The nuclear deiminase PADI4 regulates embryonic stem cell pluripotency, however its role in adult stem cells is unknown. PADI4 is expressed most highly in the bone marrow (BM), where it is found as part of a self-renewal-associated gene signature and shown to modulate the function of critical transcriptional regulators such as Tal1 and c-Myc, suggesting that it regulates haematopoietic development or regeneration. We investigated the functional significance of PADI4 in haematopoietic stem cell (HSC) biology and normal haematopoiesis. We employed two conditional mouse models of tissue-specific Padi4 ablation, where Padi4 was completely deleted either after the emergence of HSCs, or acutely in the BM of adult mice. We found that loss of PADI4 does not significantly affect HSC self-renewal or differentiation potential upon injury or serial transplantation, nor does it lead to exhaustion or premature ageing of HSCs. Thus, surprisingly, PADI4 is dispensable for cell-autonomous HSC maintenance, differentiation and haematopoietic regeneration. This work has important implications for the clinical use of PADI4 inhibitors as therapeutic agents in autoimmunity and cancer. Key PointsO_LIPADI4 is dispensable for steady-state and post-transplantation haematopoiesis C_LIO_LIHSCs do not require intrinsic PADI4 activity to respond to haematopoietic injury C_LIO_LIPADI4 deficiency does not lead to premature HSC ageing or exhaustion C_LI

developmental biology↗

bioRxiv2020

Protein citrullination was introduced into animals by horizontal gene transfer from cyanobacteria

Protein post-translational modifications (PTMs) add an enormous amount of sophistication to biological systems but their origins are largely unexplored. Citrullination, a key regulatory mechanism in human physiology and pathophysiology, is particularly enigmatic in an evolutionary context. The citrullinating enzymes peptidylarginine deiminases (PADIs) are ubiquitous across vertebrates but absent from yeast, worms and flies. Here, we map the surprising evolutionary trajectory of PADIs into the animal lineage. We present strong phylogenetic support for a clade encompassing animal and cyanobacterial PADIs that excludes fungal and other bacterial homologues. The animal and cyanobacterial PADIs share unique, functionally relevant synapomorphies that are absent from all other homologues. Molecular clock calculations and sequence divergence analyses using the fossil record estimate the last common ancestor of the cyanobacterial and animal PADIs to be approximately 1 billion years old, far younger than the 3.35-4.52 billion years known to separate bacterial and eukaryotic lineages. Under an assumption of vertical descent, PADI sequence change is anachronistically slow during this evolutionary time frame, even when compared to mitochondrial proteins, products of likely endosymbiont gene transfer and some of the most highly conserved proteins in life. The consilience of evidence indicates that PADIs were introduced from cyanobacteria into animals by horizontal gene transfer (HGT). The ancestral cyanobacterial protein is enzymatically active and can citrullinate eukaryotic proteins, suggesting that the PADI HGT event introduced a new catalytic capability into the regulatory repertoire of animals. This study reveals the unusual evolution of a pleiotropic protein modification with clear relevance in human physiology and disease.

evolutionary biology↗