Fig. 8. Early heterotopias and defects of preplate derivatives in Wnt1-Tg mice. (A, part a) Immunohistochemical staining in wild-type and Wnt1-Tg mice at 13.5 dpc showed a marked reduction in the number of Calretinin-positive cells and processes (arrowheads) within the marginal zone and subplate of Wnt1-Tg transgenic mice in anterior and lateral neocortex. (A, part b) In situ hybridization for reelin mRNA transcripts demonstrated a similar reduction of Cajal-Retzius cells in the same distribution (arrowheads). Note that the cortex of Wnt1-Tg mice also exhibited a marked increase in size. (All sections cut in the horizontal plane; boxed regions correspond to sections photographed in B, parts a-l). (B, parts a-f) Analysis of anterior regions of the neocortex of Wnt1 transgenic animals showed a loss of calretinin-positive processes and cells within the marginal zone and subplate as well as loss of reelin-positive Cajal-Retzius cells within the marginal zone at 13.5 dpc. (B, parts g-l) Reductions in cell number and processes were not as evident in more posterior regions of neocortex. No significant abnormalities of cortical plate architecture were detected in Wnt1-Tg animals by Hematoxylin and Eosin morphological evaluation (a,b,g,h). (C, parts a,b) Heterotopias were detected within the marginal zone and leptomeninges at 13.5 dpc in Wnt1-Tg mice (b) by Hematoxylin and Eosin staining (arrowheads, broken lines) and were associated with defects in the subplate morphology. (C, part c) Marginal zone heterotopias were not consistently associated with an absence of calretinin-positive cells as some positive cells were detected in close proximity to an overlying heterotopia (arrowheads). (C, part d) Defects in the laminin-positive pial basement membrane were not detected in association with or distant from Wnt1-Tg heterotopias (white arrowheads), or at any other location by immunohistochemistry at 13.5 dpc. mz, marginal zone; cp, cortical plate; sp,subplate.