Molecular and cellular underpinnings of primate cortical precursor identity and behavior: a step towards understanding normal and pathological human cortical development – PRIMACOR

The cell biology technics and the time lapse video microscopy implemented on organotypic slice preparations can observe live and in real time the behavior of proliferation, differentiation, and migration of the cerebral cortex neuron in the physiological environment. Genetic analyzes conducted at the single cell, will provide information on the molecular heterogeneity of the diversity of progenitors cortex

Our data show that the spindle size asymmetry (SSA) is a highly conserved mechanism from the Invertebrates to mammals. It is also operating in the primate cortex to generate asymmetric cell division. We have also established a reliable and efficient technique to assess SSA (Delaunay et al., 2015).
The significance of the morphological diversity of OSVZ primate progenitors is further reinforced by our modelling approach based on unsupervised categorisation of cell lineages (Pfeiffer et al., 2016).
We have explored the role of the OSVZ in generating the human cortex complexity (Dehay et al., 2015).

Developmental anomalies of the cortex can cause severe neurological and neuropsychiatric disorders, including epilepsy, intellectual disability and autism. The identification of the cell and molecular mechanisms that govern corticogenesis is central to advance the understanding, diagnosis and eventually management of human neurological disease. Given the limitation of the rodent model for studies in corticogenesis, the present proposal on NHP fundamental mechanisms of cortical development will provide key answers related to the mechanisms regulating proliferation and differentiation of cortical precursors in humans. The results will also provide insight in the mechanisms whereby cortical progenitor cells produce neurons, an information that can be used for cell based therapies to treat diseases of the nervous system.

Delaunay D, Robini MC, Dehay C. Mitotic spindle asymmetry in rodents and primates: 2D vs. 3D measurement methodologies. Front Cell Neurosci. 2015; 9:33.
Dehay C, Kennedy H, Kosik KS. The Outer Subventricular Zone and Primate-Specific Cortical Complexification. Neuron. 2015; 85(4):683-94.
Pfeiffer M, Betizeau M, Waltispurger J, Pfister SS, Douglas RJ, Kennedy H, Dehay C. Unsupervised lineage-based characterization of primate precursors reveals high proliferative and morphological diversity in the OSVZ. J Comp Neurol. 2016; 524(3):535-63.

There is a pressing need to progress in unraveling the regulatory cell and molecular mechanisms of the primate cerebral cortex development, using the macaque as a non-human primate (NHP) model for understanding key issues of human corticogeneisis. Unlike the developing rodent cortex, the developing primate cortex contains a massively expanded outer proliferative zone: the Outer Sub Ventricular Zone (OSVZ) that we have shown accounts for the production of the expanded supragranulayers in this order (*Smart et al., Cereb Cortex, 2002 ; *Lukaszewicz et al., Neuron, 2005 ; *Betizeau et al. , Neuron, 2013).
Cortical precursors in the OSVZ of the NHP are characterised by a much higher diversity than that found in the rodent SVZ, and display complex non-hierarchical lineage relationships and considerable higher proliferative abilities than expected (*Betizeau et al., Neuron, 2013). Note, we also found that a high fraction of the primate-specific miRNAs that uniquely distinguish VZ and OSVZ in the embryonic NHP cortex target cell-cycle gene regulation (*Arcila et al., Neuron, 2014). Here, building on our genetic characterization VZ and OSVZ progenitors at the population level (*Arcila et al., Neuron, 2014), we shall explore the molecular identity of OSVZ precursors using single cell genetic profiling. Specifically, miRNA expression analysis in individual OSVZ precursors will shed light on the gene regulation that drives the high degree of cellular heterogeneity in primate cortical precursors.
The cell mechanisms controlling the extensive cycling behavior and mode of division of the pseudo-epithelial OSVZ precursors have only preliminary attention. Here, we shall explore the role of a recently described mechanism operating during mouse corticogenesis: mitotic spindle asymmetry (SSA). Building on our demonstration of SSA regulating the mode of division of mouse cortical precursors (*Delaunay et al., 2014), we shall determine the occurrence and role of SSA during primate corticogenesis using a combination of in situ, ex vivo and in vitro approaches. In parallel, we shall examine the role of the Wnt signaling on SSA and the proliferative behavior of different OSVZ precursor types.
One major characteristic of OSVZ progenitors is their lack of a full epithelial structure, combined with a much less pronounced apico-basal polarity (*Betizeau et al., Neuron, 2013), both properties essential for the controlled proliferation of VZ precursors. Engineered micropatterns will be used to explore and modulate in vitro the microenvironment of OSVZ precursors in order to identify the niche and mechanical-related differences between VZ and OSVZ progenitor polarity and proliferative behavior.
Major rodent-primate differences in early Pax6 expression and regulation have been recently reported (Zhang et al., Cell Stem Cell, 2010). Although the function of Pax6 as a high-level transcription factor controlling canonical processes of rodent corticogenesis has been well characterised, its function is yet to be investigated in primate corticogenesis. Here in collaboration with David Price (Edinburgh, UK) we shall characterize rodent-primate differences in the role of Pax6. The Price lab recently showed a G1 phase-related Pax6 control of cortical progenitor proliferation in mouse (*Mi et al., Neuron, 2013). Given the differences in primate rodent time course of cell-cycle regulation and differentiation (*Betizeau et al., Neuron, 2013) we shall characterize the role of the transcription factor Pax6 during primate corticogenesis and in particular its impact on the stage-specific cell-cycle regulation, self-renewal and differentiation of cortical precursors.

* indicate publications of the applicant teams