Fig. 6. Rate of cellular proliferation is high in the SMP. (A) Bright-field illumination of an E10.5 embryonic gut showing the mesenchyme that surrounds the endoderm and the refractive properties of the SMP (broken lines). (B) The gut endoderm present in A is highlighted using an antibody specific to the endodermal-specific marker HNF3ß. (D-F) Representative sections through the spleno-pancreatic region (E), the stomach region (D) and the posterior gut region (F) at positions indicated in B. Analysis of BrdU incorporation in the developing embryonic gut; cellular incorporation of BrdU is indicated by green (low level) and yellow (high level) stains. Percent incorporation of BrdU from these regions is quantified in G; the high incorporation in the SMP is highlighted in red. (C) Transverse section through the region of dorsal pancreatic bud to give an overview of BrdU incorporation in tissues. There is high incorporation in the SMP (white arrowheads) relative to other tissues. (D) The thin mesothelial layer (white arrowheads) associated with the stomach (ML in G) and the lateral coelomic mesothelium (blue arrowheads) (lateral in G), and (E) the SMP (white arrowheads) and lateral coelomic mesothelium (blue arrowheads) (lateral in G) were also analysed. Sections through the gut posterior to the pancreatic bud (F) were also analysed but are not included in G. d, duodenum; da, doral aorta; dp dorsal pancreas; flb, forelimb bud; lb, lung buds; nt, neural tube; st, stomach; vp, ventral pancreatic bud.