Abstract
BackgroundRecent discoveries suggest that arealization of the mammalian cortical sheet develops in a manner consonant with principles established for embryonic patterning of the body. Signaling centers release morphogens that determine regional growth and tissue identity by regulating regional expression of transcription factors. Research on mouse cortex has identified several candidate morphogens that affect anteroposterior or mediolateral cortical regionalization as well as mitogenesis. Inbred strains of laboratory mice can be exploited to study cortical area map formation if there are significant phenotypic differences with which to correlate gene polymorphism or expression data. Here we describe differences in the cortical area map of two commonly used inbred strains of laboratory mice, C57BL/6J and DBA/2J. Complete cortical hemispheres from adult mice were dissected and stained for the cytochrome oxidase enzyme in order to measure histochemically defined cortical areas.ResultsC57BL/6J has the larger neocortex, relatively larger primary visual cortex (V1), but relatively smaller posterior medial barrel subfield of the primary somatosensory cortex (PMBSF). The sample of C57BL/6J and DBA/2J mice can be discriminated with 90% accuracy on the basis of these three size dimensions.ConclusionC57BL/6J and DBA/2J have markedly different cortical area maps, suggesting that inbred strains harbor enough phenotypic variation to encourage a forward genetic approach to understanding cortical development, complementing other approaches.
Highlights
Recent discoveries suggest that arealization of the mammalian cortical sheet develops in a manner consonant with principles established for embryonic patterning of the body
Visual cortex, and barrel cortex differ between C57BL/6J and DBA/2J Using established histochemical methods to visualize neocortical and primary cortical areas, we estimate that neocortex (C) is on average 7% larger in C57BL/6J (38.0 mm2) compared to DBA/2J (35.5 mm2) (F1,28 = 4.25, P = 0.049)
While both visual cortex and barrel (PMBSF) cortex areas significantly correlate with total neocortex area, each uniquely differs between strains
Summary
Recent discoveries suggest that arealization of the mammalian cortical sheet develops in a manner consonant with principles established for embryonic patterning of the body. Inbred strains of laboratory mice can be exploited to study cortical area map formation if there are significant phenotypic differences with which to correlate gene polymorphism or expression data. We describe differences in the cortical area map of two commonly used inbred strains of laboratory mice, C57BL/6J and DBA/2J. Species differences in cortical regionalization reflect genetic and epigenetic developmental programs that are presumed adaptations to different ecological niches. Krubitzer and Kahn [1] review that the mouse, ghost bat, and short-tailed opossum have approximately the same size cortical sheet, but differ substantially in the size of one of three primary sensory cortical areas. The enlarged cortical area in each species reflects a greater behavioral reliance on the represented sensory modality. As discussed by Krubitzer and Kahn [1], differences in genetic determination are well implicated by these species differences, identity of the genes and their developmental actions are not well understood
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