High levels of Ngn3 expression in pancreatic progenitor cells are both necessary and sufficient to initiate endocrine differentiation. While it is clear that the Notch-Hes1-mediated signals control the number of Ngn3-expressing cells in the developing pancreas, it is not known what factors control the level of Ngn3 expression in individual pancreatic cells. Here we report that Myt1b and Ngn3 form a feed-forward expression loop that regulates endocrine differentiation. Myt1b induces glucagon expression by potentiating Ngn3 transcription in pancreatic progenitors. Vice versa, Ngn3 protein production induces the expression of Myt1. Furthermore, pancreatic Myt1 expression largely, but not totally, relies on Ngn3 activity. Surprisingly, a portion of Myt1 expressing pancreatic cells express glucagon and other α cell markers in Ngn3 nullizygous mutant animals. These results demonstrate that Myt1b and Ngn3 positively regulate each other's expression to promote endocrine differentiation. In addition, the data uncover an unexpected Ngn3 expression-independent endocrine cell production pathway, which further bolsters the notion that the seemingly equivalent endocrine cells of each type, as judged by hormone and transcription factor expression, are heterogeneous in their origin.
Bibliographical noteFunding Information:
We thank Chris Wright, Anne Grapin-Botton, Chin Chiang, Anna Means, and Roland Stein for useful discussions. We also thank the staff of the Vanderbilt Transgenic/ES Cell Shared Resource for expert performance of the blastocyst microinjection experiments and Sean Schaffer in the Vanderbilt Cell Imaging Shared Resource for help with confocal imaging. This research was supported by grants from the NIH (1RO1 DK065949-01A1 to GG), a JDRF Career Development Award (# 2003-651) to GG. P.S. was supported by the JDRF, the EU 6th Framework Program, and the NIH (grant DK072473).
- Endocrine islet
- Endocrine progenitor