Bajpai, V. K. | bioRxiv Science

bioRxiv2021

A genome-wide genetic screen uncovers novel determinants of human pigmentation

The skin color is one of the most diverse human traits and is determined by the quantity, type and distribution of melanin. Here, we leverage light scattering properties of melanin to conduct a genome-wide CRISPR-Cas9 screen for novel regulators of melanogenesis. We identify functionally diverse genes converging on melanosome biogenesis, endosomal transport and transcriptional/posttranscriptional gene regulation, most of which represent novel associations with pigmentation. A survey of transcriptomes from diversely pigmented individuals reveals that the majority of genes discovered in our screen are upregulated in dark skin melanocytes, in agreement with their melanin-promoting function and potential contribution to skin color variation. This association is further buttressed by the significant skin color heritability enrichment in the vicinity of these genes. Taken together, our study presents a novel approach to assay pigmentation and uncovers a plethora of melanogenesis regulators, with broad implications for human variation, cell biology and medicine. One Sentence SummaryGenetic screen uncovers genes involved in human melanogenesis, many of which are differentially expressed in individuals of diverse skin color.

cell biology↗

bioRxiv2019

Cross-species blastocyst chimerism between nonhuman primates using iPSCs

Through the production of chimeric animals, induced pluripotent stem cells (iPSCs) can generate personalized organs with diverse applications for both basic research and translational medicine. This concept was first validated in rodents by forming a rat pancreas in mice and vice versa. However, the potential use of human iPSCs to generate xenogenic organs in other species is technically and ethically difficult. Recognizing these concerns, we explored the generation of chimeric nonhuman primates (NHP) embryos, by injecting either chimpanzee or pig-tailed macaque iPSCs into rhesus macaque embryos. We first derived iPSCs from chimpanzees and pig-tailed macaques. We found that the chimpanzee iPSCs mixed well with human iPSCs during in vitro co-culture and differentiation. The differentiation of mixed human and chimpanzee iPSCs formed functioning cardiomyocyte layers in vitro, whereas human or chimpanzee iPSC mixed with pig-tailed macaque or mouse cells do not; these results indicate that chimpanzee and human cells are closely related in function. Considering the ethical aspects of injecting human iPSCs into nonhuman primate blastocysts, we tested whether chimpanzee iPSCs injected into 99 macaque 5-day-old embryos formed cross-species chimeras two days after injection. Strikingly, the chimpanzee iPSCs survived, proliferated and integrated near the inner cell mass (ICM) of rhesus macaque embryos. These findings highlight the broad potential of primate iPSCs in forming cross-species chimeras beyond rodents and provides a foundational basis for organ generation using human iPSCs.

developmental biology↗