Fig. 1. Development of the preplate in 3 integrin-deficient mice. Neurons that are destined to the preplate of cerebral cortex were labeled at birth (E10.5 or E11.5) with BrdU, and their location was analyzed at E17, following the splitting of the preplate into marginal zone and subplate by invading migratory neurons. BrdU immunoreactivity was visualized with Cy3 and nuclei were counterstained with bis benzimide. When neurons were birthdated at E10.5, in wild-type mice, BrdU-labeled neurons were found in the marginal zone (arrows) and subplate layers (arrowheads) of cerebral cortex, as expected (A). Similar distribution was also seen in 3 integrin-deficient cortex (B). When neurons were birthdated at E11.5, most of the labeled neurons in wild-type cortex were found in subplate and few in the marginal zone (C). Identical pattern of labeling is also evident in 3 integrin-deficient cortex (D). Together, these results indicate that the preplate develops and splits normally in the absence of ₃ integrin. MZ, marginal zone; CP, cortical plate; SP, subplate; IZ, intermediate zone. Scale bar: 60 µm.