As our closest living relatives, non-human primates uniquely enable explorations of human health, disease, development, and evolution. Considerable effort has thus been devoted to generating induced pluripotent stem cells (iPSCs) from multiple non-human primate species. Here, we establish improved culture methods for chimpanzee (Pan troglodytes) and pig-tailed macaque (Macaca nemestrina) iPSCs. Such iPSCs spontaneously differentiate in conventional culture conditions, but can be readily propagated by inhibiting endogenous WNT signaling. As a unique functional test of these iPSCs, we injected them into the pre-implantation embryos of another non-human species, rhesus macaques (Macaca mulatta). Ectopic expression of gene BCL2 enhances the survival and proliferation of chimpanzee and pig-tailed macaque iPSCs within the pre-implantation embryo, although the identity and long-term contribution of the transplanted cells warrants further investigation. In summary, we disclose transcriptomic and proteomic data, cell lines, and cell culture resources that may be broadly enabling for non-human primate iPSCs research.

For more than 50 years, the methylation of mammalian actin at histidine 73 has been known to occur¹. Despite the pervasiveness of His73 methylation, which we find is conserved in several model animals and plants, its function remains unclear and the enzyme that generates this modification is unknown. Here we identify SET domain protein 3 (SETD3) as the physiological actin His73 methyltransferase. Structural studies reveal that an extensive network of interactions clamps the actin peptide onto the surface of SETD3 to orient His73 correctly within the catalytic pocket and to facilitate methyl transfer. His73 methylation reduces the nucleotide-exchange rate on actin monomers and modestly accelerates the assembly of actin filaments. Mice that lack SETD3 show complete loss of actin His73 methylation in several tissues, and quantitative proteomics analysis shows that actin His73 methylation is the only detectable physiological substrate of SETD3. SETD3-deficient female mice have severely decreased litter sizes owing to primary maternal dystocia that is refractory to ecbolic induction agents. Furthermore, depletion of SETD3 impairs signal-induced contraction in primary human uterine smooth muscle cells. Together, our results identify a mammalian histidine methyltransferase and uncover a pivotal role for SETD3 and actin His73 methylation in the regulation of smooth muscle contractility. Our data also support the broader hypothesis that protein histidine methylation acts as a common regulatory mechanism.

The disialoganglioside GD2 is overexpressed on several solid tumors, and monoclonal antibodies targeting GD2 have substantially improved outcomes for children with high-risk neuroblastoma. However, approximately 40% of patients with neuroblastoma still relapse, and anti-GD2 has not mediated significant clinical activity in any other GD2⁺ malignancy. Macrophages are important mediators of anti-tumor immunity, but tumors resist macrophage phagocytosis through expression of the checkpoint molecule CD47, a so-called 'Don't eat me' signal. In this study, we establish potent synergy for the combination of anti-GD2 and anti-CD47 in syngeneic and xenograft mouse models of neuroblastoma, where the combination eradicates tumors, as well as osteosarcoma and small-cell lung cancer, where the combination significantly reduces tumor burden and extends survival. This synergy is driven by two GD2-specific factors that reorient the balance of macrophage activity. Ligation of GD2 on tumor cells (a) causes upregulation of surface calreticulin, a pro-phagocytic 'Eat me' signal that primes cells for removal and (b) interrupts the interaction of GD2 with its newly identified ligand, the inhibitory immunoreceptor Siglec-7. This work credentials the combination of anti-GD2 and anti-CD47 for clinical translation and suggests that CD47 blockade will be most efficacious in combination with monoclonal antibodies that alter additional pro- and anti-phagocytic signals within the tumor microenvironment.