Functional Verification of Novel ELMO1 Variants by Live Imaging in Zebrafish

Diverse gut pathogens exploit the host engulfment pathway via a conserved mechanism

Macrophages clear infections by engulfing and digesting pathogens within phagolysosomes. Pathogens escape this fate by engaging in a molecular arms race; they use WxxxE motif-containing "effector" proteins to subvert the host cells they invade and seek refuge within protective vacuoles. Here, we define the host component of the molecular arms race as an evolutionarily conserved polar "hot spot" on the PH domain of ELMO1 (Engulfment and Cell Motility protein 1), which is targeted by diverse WxxxE effectors. Using homology modeling and site-directed mutagenesis, we show that a lysine triad within the "patch" directly binds all WxxxE effectors tested: SifA (Salmonella), IpgB1 and IpgB2 (Shigella), and Map (enteropathogenic Escherichia coli). Using an integrated SifA-host protein-protein interaction network, in silico network perturbation, and functional studies, we show that the major consequences of preventing SifA-ELMO1 interaction are reduced Rac1 activity and microbial invasion. That multiple effectors of diverse structure, function, and sequence bind the same hot spot on ELMO1 suggests that the WxxxE effector(s)-ELMO1 interface is a convergence point of intrusion detection and/or host vulnerability. We conclude that the interface may represent the fault line in coevolved molecular adaptations between pathogens and the host, and its disruption may serve as a therapeutic strategy.

Diverse Gut Pathogens Exploit the Host Engulfment Pathway via a Conserved Mechanism

Macrophages clear infections by engulfing and digesting pathogens within phagolysosomes. Pathogens escape this fate by engaging in a molecular arms race; they use WxxxE motif-containing effector proteins to subvert the host cells they invade and seek refuge within protective vacuoles. Here we define the host component of the molecular arms race as an evolutionarily conserved polar hotspot on the PH-domain of ELMO1 (Engulfment and Cell Motility1), which is targeted by diverse WxxxE-effectors. Using homology modeling and site-directed mutagenesis, we show that a lysine triad within the patch directly binds all WxxxE-effectors tested: SifA (Salmonella), IpgB1 and IpgB2 (Shigella), and Map (enteropathogenic E. coli). Using an integrated SifA-host protein-protein interaction (PPI) network, in-silico network perturbation, and functional studies we show that the major consequences of preventing SifA-ELMO1 interaction are reduced Rac1 activity and microbial invasion. That multiple effectors of diverse structure, function, and sequence bind the same hotpot on ELMO1 suggests that the WxxxE-effector(s)-ELMO1 interface is a convergence point of intrusion detection and/or host vulnerability. We conclude that the interface may represent the fault line in co-evolved molecular adaptations between pathogens and the host and its disruption may serve as a therapeutic strategy.

The oocyte cumulus complex regulates mouse sperm migration in the oviduct

As the time of ovulation draws near, mouse spermatozoa move out of the isthmic reservoir, which is a prerequisite for fertilization. However, the molecular mechanism remains unclear. The present study revealed that mouse cumulus cells of oocytes-cumulus complexes (OCCs) expressed transforming growth factor-β ligand 1 (TGFB1), whereas ampullary epithelial cells expressed the TGF-β receptors, TGFBR1 and TGFBR2, and all were upregulated by luteinizing hormone (LH)/human chorionic gonadotropin (hCG). OCCs and TGFB1 increased natriuretic peptide type C (NPPC) expression in cultured ampullae via TGF-β signaling, and NPPC treatment promoted spermatozoa moving out of the isthmic reservoir of the preovulatory oviducts. Deletion of Tgfb1 in cumulus cells and Tgfbr2 in ampullary epithelial cells blocked OCC-induced NPPC expression and spermatozoa moving out of the isthmic reservoir, resulting in compromised fertilization and fertility. Oocyte-derived paracrine factors were required for promoting cumulus cell expression of TGFB1. Therefore, oocyte-dependent and cumulus cell-derived TGFB1 promotes the expression of NPPC in oviductal ampulla, which is critical for sperm migration in the oviduct and subsequent fertilization.

Csf1rb regulates definitive hematopoiesis in zebrafish

In vertebrates, hematopoietic stem and progenitor cells (HSPCs) are capable of self-renewal and continuously replenishing all mature blood lineages throughout life. However, the molecular signaling regulating the maintenance and expansion of HSPCs remains incompletely understood. Colony-stimulating factor 1 receptor (CSF1R) is believed to be the primary regulator for the myeloid lineage but not HSPC development. Here, we show a surprising role of Csf1rb, a zebrafish homolog of mammalian CSF1R, in preserving the HSPC pool by maintaining the proliferation of HSPCs. Deficiency of csf1rb leads to a reduction in both HSPCs and their differentiated progenies, including myeloid, lymphoid and erythroid cells at early developmental stages. Likewise, the absence of csf1rb conferred similar defects upon HSPCs and leukocytes in adulthood. Furthermore, adult hematopoietic cells from csf1rb mutants failed to repopulate immunodeficient zebrafish. Interestingly, loss-of-function and gain-of-function assays suggested that the canonical ligands for Csf1r in zebrafish, including Csf1a, Csf1b and Il34, were unlikely to be ligands of Csf1rb. Thus, our data indicate a previously unappreciated role of Csf1r in maintaining HSPCs, independently of known ligands.