The growth factor EPIREGULIN promotes basal progenitor cell proliferation in the developing neocortex

Canonical and non-canonical PRC1 differentially contribute to regulation of neural stem cell fate

Neocortex development is characterized by sequential phases of neural progenitor cell (NPC) expansion, neurogenesis, and gliogenesis. Polycomb-mediated epigenetic mechanisms are known to play important roles in regulating the lineage potential of NPCs during development. The composition of Polycomb repressive complex 1 (PRC1) is highly diverse in mammals and was hypothesized to contribute to context-specific regulation of cell fate. Here, we have performed a side-by-side comparison of the role of canonical PRC1.2/1.4 and non-canonical PRC1.3/1.5, all of which are expressed in the developing neocortex, in NSC proliferation and differentiation. We found that the deletion of Pcgf2/4 in NSCs led to a strong reduction in proliferation and to altered lineage fate, both during the neurogenic and gliogenic phase, whereas Pcgf3/5 played a minor role. Mechanistically, genes encoding stem cell and neurogenic factors were bound by PRC1 and differentially expressed upon Pcgf2/4 deletion. Thus, rather than different PRC1 subcomplexes contributing to different phases of neural development, we found that canonical PRC1 played a more significant role in NSC regulation during proliferative, neurogenic, and gliogenic phases compared with non-canonical PRC1.

Epigenetic and metabolic regulation of developmental timing in neocortex evolution

The human brain is characterized by impressive cognitive abilities. The neocortex is the seat of higher cognition, and neocortex expansion is a hallmark of human evolution. While developmental programs are similar in different species, the timing of developmental transitions and the capacity of neural progenitor cells (NPCs) to proliferate differ, contributing to the increased production of neurons during human cortical development. Here, we review the epigenetic regulation of developmental transitions during corticogenesis, focusing mostly on humans while building on knowledge from studies in mice. We discuss metabolic-epigenetic interplay as a potential mechanism to integrate extracellular signals into neural chromatin. Moreover, we synthesize current understanding of how epigenetic and metabolic deregulation can cause neurodevelopmental disorders. Finally, we outline how developmental timing can be investigated using brain organoid models.

Indirect neurogenesis in space and time

During central nervous system (CNS) development, neural progenitor cells (NPCs) generate neurons and glia in two different ways. In direct neurogenesis, daughter cells differentiate directly into neurons or glia, whereas in indirect neurogenesis, neurons or glia are generated after one or more daughter cell divisions. Intriguingly, indirect neurogenesis is not stochastically deployed and plays instructive roles during CNS development: increased generation of cells from specific lineages; increased generation of early or late-born cell types within a lineage; and increased cell diversification. Increased indirect neurogenesis might contribute to the anterior CNS expansion evident throughout the Bilateria and help to modify brain-region size without requiring increased NPC numbers or extended neurogenesis. Increased indirect neurogenesis could be an evolutionary driver of the gyrencephalic (that is, folded) cortex that emerged during mammalian evolution and might even have increased during hominid evolution. Thus, selection of indirect versus direct neurogenesis provides a powerful developmental and evolutionary instrument that drives not only the evolution of CNS complexity but also brain expansion and modulation of brain-region size, and thereby the evolution of increasingly advanced cognitive abilities. This Review describes indirect neurogenesis in several model species and humans, and highlights some of the molecular genetic mechanisms that control this important process.

Epi-regulate my brain: unlocking mechanisms of brain growth evolution

A new study sheds light on the mechanisms of cerebral cortex expansion during evolution.