Unravelling differences between human and chimpanzee NSPC behaviour is therefore a key issue, yet very little is known about such differences. This reflects primarily a greater and prolonged proliferative capacity of human neural stem and progenitor cells (NSPCs) within the germinal zones of the developing neocortex ( Lewitus et al., 2013). Neocortex expansion in humans relative to chimpanzees involves an increase in the number of cortical neurons generated during fetal development ( Borrell and Reillo, 2012 Florio and Huttner, 2014 Herculano-Houzel, 2009 Lui et al., 2011). The expansion of the neocortex during primate evolution is thought to contribute to the higher cognitive capacity of humans compared to our closest living relatives, the great apes, and notably the chimpanzees ( Geschwind and Rakic, 2013 Rakic, 2009 Striedter, 2005). This suggests that a longer metaphase may be a feature of brain stem cells.įurther studies are now needed to find out how the length of time these progenitor cells spend in metaphase affects how chimpanzee and human brains develop and whether this can help explain why the human brain is so much larger. also found that progenitor cells more likely to become neurons sooner had a shorter metaphase than progenitor cells more likely to remain proliferating as stem cells for longer. Metaphase is the part of the division process when the cell makes sure that structures called chromosomes, which carry the cell’s DNA, can be separated and distributed equally between the two daughter cells. then used live microscopy to show that progenitor cells that form the human cerebral cortex spend around 50% more time in a stage of the cell division process called metaphase compared to the same cells from chimpanzees or orangutans. The experiments showed that the human and chimpanzee brain organoids were remarkably similar in many ways including in the mix of cell types and in how these cells were arranged. have now analysed brain organoids grown from reprogrammed human, chimpanzee and orangutan cells. Mora-Bermúdez, Badsha, Kanton, Camp et al. Recently, researchers have been able to use these reprogrammed cells to make tissue that resembles the brain in petri dishes, known as brain organoids. Under the right conditions, cells collected from adult humans and other animals can be reprogrammed to behave like brain stem cells. To study the earliest stages of brain development, researchers often use human brain cells grown in the laboratory. How these species differences arise is not clear, but it likely occurs in the earliest phases of development when brain stem and progenitor cells divide and give rise to cerebral cortex cells in the growing brain. Networks of brain cells in the cerebral cortex also behave differently in the two species. Moreover, a part of the brain called the cerebral cortex – which plays a key role in memory, attention, awareness and thought – contains twice as many cells in humans as the same region in chimpanzees. The human brain is about three times as big as the brain of our closest living relative, the chimpanzee. These subtle differences in cortical progenitors between humans and chimpanzees may have consequences for human neocortex evolution. Consistent with this, the small set of genes more highly expressed in human apical progenitors points to increased proliferative capacity, and the proportion of neurogenic basal progenitors is lower in humans. Notably, however, live imaging of apical progenitor mitosis uncovered a lengthening of prometaphase-metaphase in humans compared to chimpanzees that is specific to proliferating progenitors and not observed in non-neural cells. We find that the cytoarchitecture, cell type composition, and neurogenic gene expression programs of humans and chimpanzees are remarkably similar. Here, we have searched for such differences by analysing cerebral organoids from human and chimpanzees using immunohistofluorescence, live imaging, and single-cell transcriptomics. This expansion is thought to primarily reflect differences in proliferation versus differentiation of neural progenitors during cortical development. Human neocortex expansion likely contributed to the remarkable cognitive abilities of humans.
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