Trigger of twin-fights in captive common marmosets.

Common marmosets usually give birth to twins and form a social group consisting of a breeding couple and pairs of same-aged siblings. The twins may engage in the first agonistic fights between them, twin-fights (TFs), during adolescence. This study investigated the TFs based on records accumulated in our captive colony over 12 years to elucidate the proximate causations that trigger the TFs. We aimed to determine whether the TF onset mainly depended on internal events (such as the onset of puberty) as previously suggested or external events (such as the birth of the younger siblings and the behavioral change of the group members). Although both events usually occur simultaneously, the birth control method (i.e., manipulation of ovulation and interbirth-intervals by prostaglandin administration to females) could temporally separate these events. A comparison of the onset day and occurrence rate with or without the birth control procedure revealed that TFs were triggered by a combination of internal and external events, that is, external events were the predominant triggers of TF, under the influence of internal events. The timing of TF onset was significantly delayed when the birth of the younger siblings was delayed and the twins grew older under the birth-controlled condition, suggesting that the birth of younger siblings and related behavioral changes of group members, as well as twins' developmental maturation, could trigger TF. Higher TF rates between same-sex twins were consistent with previous studies, reflecting the characteristics of same-sex directed aggression in callitrichines.

Early neurogenic properties of iPSC-derived neurosphere formation in Japanese macaque monkeys.

Non-human primates are important models for investigations of neural development and evolution, and the use of Japanese macaque monkeys has especially contributed to the advancement of neuroscience studies. However, these studies are restricted by the number of animals able to be evaluated and the invasiveness of the methodologies. Induced pluripotent stem cells (iPSCs) can provide an alternative strategy for investigating neural development in vitro. We have established direct neurosphere (dNS) formation cultures of primate iPSCs as an in vitro model of early neurodevelopment in primate species. Here, we used dNS formation and neuronal differentiation cultures established from Japanese macaque iPSCs (jm-iPSCs) to investigate the usefulness of these cells as an in vitro model of early neural development. Time-course analyses of developmental potency and gene expression kinetics were performed during dNS formation culture of jm-iPSCs. During a 1-week culture, jm-iPSC-derived dNSs became neurogenic by day 3 and underwent stepwise expression changes of key developmental regulators along early neural development in a similar manner to chimpanzee dNS formation previously reported. Meanwhile, a subset of genes, including CYP26A1 and NPTX1, showed differential expression propensity in Japanese macaque, chimpanzee, and human iPSC-derived dNSs. Spontaneous upregulation of NOTCH signaling-associated genes HES5 and DLL1 was also observed in neuronal differentiation cultures of Japanese macaque but not chimpanzee dNSs, possibly reflecting the earlier neurogenic competence in Japanese macaques. The use of jm-iPSCs provides an alternative approach to neurological studies of primate development. Furthermore, jm-iPSCs can be used to investigate species differences in early neural development that are key to primate evolution.

Cardiac differentiation of chimpanzee induced pluripotent stem cell lines with different subspecies backgrounds.

The comparative analysis between humans and non-human primates is an instrumental approach for elucidating the evolutional traits and disease propensity of humans. However, in primates, cross-species analyses of their developmental events have encountered constraints because of the ethical and technical limitations in available sample collection, sequential monitoring, and manipulations. In an endeavor to surmount these challenges, in recent years, induced pluripotent stem cells (iPSCs) have garnered escalating interest as an in vitro tool for cross-species analyses between humans and non-human primates. Meanwhile, compared to humans, there is less information on in vitro differentiation of non-human primate iPSCs, and their genetic diversity including subspecies may cause different eligibility to in vitro differentiation methods. Therefore, antecedent to embarking on a comparative analysis to humans, it is a prerequisite to develop the efficacious methodologies for in vitro differentiation regardless of the intraspecies genetic background in non-human primates. In this study, we executed the in vitro differentiation of cardiomyocytes from four chimpanzee iPSC lines with different subspecies and individual backgrounds. To induce cardiomyocytes from chimpanzee iPSCs, we evaluated our methodology for in vitro cardiac differentiation of human iPSCs. Eventually, with minor alterations, our cardiac differentiation method was applicable to all chimpanzee iPSC lines tested as assessed by the expression of cardiac marker genes and the beating ability. Hence, our in vitro differentiation method will advance iPSC-based research of chimpanzee cardiac development and also hold possible utility to cross-species analyses among primate species.

Generation of chimpanzee induced pluripotent stem cell lines for cross-species comparisons.

As humans' closest living relatives, chimpanzees offer valuable insights into human evolution. However, technical and ethical limitations hinder investigations into the molecular and cellular foundations that distinguish chimpanzee and human traits. Recently, induced pluripotent stem cells (iPSCs) have emerged as a novel model for functional comparative studies and provided a non-invasive alternative for studying embryonic phenomena. In this study, we generated five new chimpanzee iPSC lines from peripheral blood cells and skin fibroblasts with SeV vectors carrying four reprogramming factors (human OCT3/4, SOX2, KLF4, and L-MYC) and characterized their pluripotency and differentiation potential. We also examined the expression of a human-specific non-coding RNA, HSTR1, which is predicted to be involved in human brain development. Our results show that the chimpanzee iPSCs possess pluripotent characteristics and can differentiate into various cell lineages. Moreover, we found that HSTR1 is expressed in human iPSCs and their neural derivatives but not in chimpanzee counterparts, supporting its possible role in human-specific brain development. As iPSCs are inherently variable due to genetic and epigenetic differences in donor cells or reprogramming procedures, it is essential to expand the number of chimpanzee iPSC lines to comprehensively capture the molecular and cellular properties representative of chimpanzees. Hence, our cells provide a valuable resource for investigating the function and regulation of human-specific transcripts such as HSTR1 and for understanding human evolution more generally.