Nishimura Wataru, Kapoor Archana, El Khattabi Ilham, Jin Wanzhu, Yasuda Kazuki, Bonner-Weir Susan, Sharma Arun
Section of Islet Cell & Regenerative Biology, Joslin Diabetes Center, Boston, Massachusetts, United States of America.
Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America.
PLoS One. 2015 Nov 5;10(11):e0142286. doi: 10.1371/journal.pone.0142286. eCollection 2015.
Early in pancreatic development, epithelial cells of pancreatic buds function as primary multipotent progenitor cells (1°MPC) that specify all three pancreatic cell lineages, i.e., endocrine, acinar and duct. Bipotent "Trunk" progenitors derived from 1°MPC are implicated in directly regulating the specification of endocrine progenitors. It is unclear if this specification process is initiated in the 1°MPC where some 1°MPC become competent for later specification of endocrine progenitors. Previously we reported that in Pdx1tTA/+;tetOMafA (bigenic) mice inducing expression of transcription factor MafA in Pdx1-expressing (Pdx1+) cells throughout embryonic development inhibited the proliferation and differentiation of 1°MPC cells, resulting in reduced pancreatic mass and endocrine cells by embryonic day (E) 17.5. Induction of the transgene only until E12.5 in Pdx1+ 1°MPC was sufficient for this inhibition of endocrine cells and pancreatic mass at E17.5. However, by birth (P0), as we now report, such bigenic pups had significantly increased pancreatic and endocrine volumes with endocrine clusters containing all pancreatic endocrine cell types. The increase in endocrine cells resulted from a higher proliferation of tubular epithelial cells expressing the progenitor marker Glut2 in E17.5 bigenic embryos and increased number of Neurog3-expressing cells at E19.5. A BrdU-labeling study demonstrated that inhibiting proliferation of 1°MPC by forced MafA-expression did not lead to retention of those progenitors in E17.5 tubular epithelium. Our data suggest that the forced MafA expression in the 1°MPC inhibits their competency to specify endocrine progenitors only until E17.5, and after that compensatory proliferation of tubular epithelium gives rise to a distinct pool of endocrine progenitors. Thus, these bigenic mice provide a novel way to characterize the competency of 1°MPC for their ability to specify endocrine progenitors, a critical limitation in our understanding of endocrine differentiation.
在胰腺发育早期，胰腺芽的上皮细胞作为主要的多能祖细胞（1°MPC）发挥作用，可分化出所有三种胰腺细胞谱系，即内分泌细胞、腺泡细胞和导管细胞。源自1°MPC的双能“主干”祖细胞参与直接调节内分泌祖细胞的分化。目前尚不清楚这种分化过程是否在1°MPC中启动，即部分1°MPC是否具备随后分化为内分泌祖细胞的能力。此前我们报道，在Pdx1tTA/+;tetOMafA（双转基因）小鼠中，在整个胚胎发育过程中诱导转录因子MafA在表达Pdx1（Pdx1+）的细胞中表达，会抑制1°MPC细胞的增殖和分化，导致在胚胎第17.5天（E17.5）时胰腺质量和内分泌细胞数量减少。仅在E12.5之前诱导Pdx1+ 1°MPC中的转基因表达，就足以在E17.5时抑制内分泌细胞和胰腺质量。然而，正如我们现在报道的，到出生时（P0），这些双转基因幼崽的胰腺和内分泌体积显著增加，内分泌细胞簇包含所有胰腺内分泌细胞类型。内分泌细胞数量的增加源于E17.5双转基因胚胎中表达祖细胞标志物Glut2的管状上皮细胞增殖增加，以及E19.5时表达Neurog3的细胞数量增加。一项BrdU标记研究表明，通过强制表达MafA抑制1°MPC的增殖，并不会导致这些祖细胞在E17.5的管状上皮中保留。我们的数据表明，在1°MPC中强制表达MafA仅在E17.5之前抑制其分化为内分泌祖细胞的能力，在此之后，管状上皮的代偿性增殖产生了一个独特的内分泌祖细胞池。因此，这些双转基因小鼠为表征1°MPC分化为内分泌祖细胞的能力提供了一种新方法，这是我们理解内分泌分化的一个关键局限。
