Fig. 6. Functional characterization of Myt1 during mouse endocrine development. (A-D) In situ hybridization showing Ngn3 and Myt1 expression at several stages of embryogenesis. A is a control showing Ngn3 expression in the developing pancreatic region (red dashed lines) at E8.5. (B) At E8.5 Myt1 is expressed at a low level in the prospective pancreatic region in a manner similar to Ngn3 (red dashed line). The prospective pancreatic region is recognized by its position below somite 8-10 (total of 15 somites), and the position of the dorsal aorta (green arrow). Strong Myt1 expression was also detected in the neural tube (black arrow). (C) At E10.5, Myt1 was detected in a scattered fashion in the pancreatic bud, within or close to duct-like structures (red arrowheads). (D) At E15.5, Myt1 expression was much reduced (see text). (E-H) Transgenic expression of dnMyt1 in endocrine progenitor cells inhibits endocrine differentiation. (E) Insulin⁺ cells in a representative wild-type pancreas. (F) Insulin⁺ cells in a representative pancreas section of a Ngn3-dnMyt1 littermate. Note fewer insulin-expressing cells in F. Similarly, the number of glucagon⁺ cells is reduced in the Ngn3-dnMyt1 expressing embryo (H) compared with that of wild type embryo (G). In E-H, Cy3-conjugated antibodies were used. Scale bar: 25 µm.