22q11 deletion selectively alters progenitor states and projection neuron identities in the developing cerebral cortex

Abstract

The developmental origin of Layer 2/3 projection neuron (PN) pathology in the frontal association cortex due to heterozygous 22q11 gene deletion--the genetic foundation of elevated risk for schizophrenia and related psychiatric disorders in 22q11.2 Deletion Syndrome (22q11DS)--reflects cell state-dependent, temporally restricted vulnerability of transcriptionally diverse subsets of intermediate progenitors and neuroblasts. The molecular and cell biological consequences of these evanescent state-dependent changes include divergent proliferative capacity of the most highly proliferative progenitors, enhanced neurogenic gene expression, altered DNA methylation, and increased numbers of immediate neuroblast progeny at peak neurogenesis in fetal frontal cortex of the LgDel 22q11DS mouse model. These altered cell states prefigure a post-natal cohort of upper layer PNs generated at the peak of Layer 2/3 PN genesis--not before or after--whose frequencies are significantly diminished and molecular identities are substantially divergent in medial frontal association, but not primary somatosensory or visual cortices. Thus, frontal association cortices in 22q11DS and schizophrenia more broadly may be pathogenic targets due to vulnerabilities of expanded, highly proliferative, transcriptionally dynamic populations of intermediate progenitors that increase L2/3 PN frequency to enhance cortico-cortical connectivity.