Fig. 1. Wee2 expression correlates with the lack of mitotic cells within the dorsal and paraxial mesoderm. (A) Panels 1 and 3 are sagittal sections of representative stage 12.5 and 18 embryos that were subjected to in situ hybridization for Wee2. Panels 2 and 4 are composite images of 10 serial sagittal sections of representative stage 12.5 and 18 embryos that were subjected to whole-mount immunocytochemistry against phospho-histone H3 (PH3). Note the absence of mitotic cells (black dots) in the dorsal and paraxial mesoderm. Dorsal towards the right, anterior towards the top. pne, presumptive neural ectoderm; dm, dorsal mesoderm; pm, paraxial mesoderm; ey, eye anlage; sm, somite. (B) Wee2 protein is expressed from mid-gastrula stages onwards. Indicated developmental stages were subject to Wee2 and Cdk1/2 western analysis.