Lengthening Neurogenic Period during Neocortical Development Causes a Hallmark of Neocortex Expansion

Length of the Neurogenic Period—A Key Determinant for the Generation of Upper-Layer Neurons During Neocortex Development and Evolution

“…In the latter scenario, there would be an increase in neuron generation rates throughout neurogenesis (Polleux et al, 1997b), which was not observed. That neuronal add-on to the existing neurogenic program occurred without altering the timing of the fate switch between deep-and upperlayer neuron production, which took place at around embryonic day 14.5 (Stepien et al, 2020), as reported previously (Saurat et al, 2013;Toma et al, 2014;Klingler et al, 2019).…”

“…We recently addressed the potentially critical role of a prolongation of the neurogenic period on increased neocortical neuron production. In a nutshell, our study directly demonstrates that lengthening of the neurogenic period can induce hallmarks of neocortex expansion, without overt alterations in the existing progenitor lineages (Stepien et al, 2020). Our study used a mouse model system to explore a possible causative relationship between the prolongation of the neurogenic period and the increased number of neocortical neurons produced, without introducing genetic changes that would affect the lineage of progenitors.…”

“…We also addressed potential mechanisms leading to the prolongation of the neurogenic period (Stepien et al, 2020). Given the correlation of upper-layer neuron production and neurogenesis length with the length of gestation, which has been found to be maternally determined in the mouse strains analyzed (Murray et al, 2010) as well as in other mammals (Zhang et al, 2017), we hypothesized that the maternal environment could provide cues controlling cortical neurogenesis timing.…”

“…Given the correlation of upper-layer neuron production and neurogenesis length with the length of gestation, which has been found to be maternally determined in the mouse strains analyzed (Murray et al, 2010) as well as in other mammals (Zhang et al, 2017), we hypothesized that the maternal environment could provide cues controlling cortical neurogenesis timing. To test this hypothesis, the embryos of the short-gestation strain were transferred into long-gestation strain foster mothers, and vice versa (Stepien et al, 2020). The short-gestation strain fetuses that developed in the maternal environment of the long-gestation strain fosters were found to specifically increase the number of upper-layer, but not deep-layer, cortical neurons generated, to the level characteristic of the foster mother phenotype.…”

From stem and progenitor cells to neurons in the developing neocortex: key differences among hominids

“…In fact, mathematical modelling has shown that the neurogenic period is a likely candidate to sufficiently explain differences in cortical neuron numbers among hominids [35]. Consistent with this modelling, which has received experimental support recently [36], the increase in size among primate brains and neocortices, from monkeys…”