Laminar specific gene expression reveals differences in postnatal laminar maturation in mouse auditory, visual, and somatosensory cortex.

Proper formation of laminar structures in sensory cortexes is critical for sensory information processing. Previous studies suggested that the timing of neuronal migration and the laminar position of cortical neurons differ among sensory cortexes. How they differ during postnatal development has not been systematically investigated. Here, identifying laminas using transcription factors, we examined postnatal changes in neuronal density and distribution in presumptive primary auditory (ACx), visual (VCx), and somatosensory cortexes (SCx) in a strain of mice using immunofluorescence techniques. Development of laminar thickness and its cortical proportion differed among the sensory cortexes. Layers 2-4 defined by Cut-like homeobox 1 (Cux1)-expressing neurons were narrower, and layer 5 was wider in ACx compared to those in VCx or SCx, while Forkhead-box protein P2 (Foxp2)-defined layer 6 was wider in SCx than the other two sensory cortexes throughout postnatal development. Meanwhile, thalamocortical input layers identified by Cux1-expressing neurons formed later in ACx than in the other two cortical regions. The cell densities of ETS-related protein 81-expressing neurons increased in both lower and upper layers but at distinct timing, while those of COUP-TF-interacting protein 2 expressing neurons in the lower layers changed bidirectionally (i.e., increased or decreased) both in layer- and cortical region-specific manners. Foxp2-expressing cells in layer 6 distributed differently and declined at different timing among the sensory cortexes. Overall, we demonstrate that the maturational timing of lamina differs among the sensory cortexes and that postnatal age-dependent changes in neuronal distribution are unique to each of the sensory cortexes.