350-OR: Parturition Event Regulates Endocrine Genesis during Pancreas Differentiation

It is essential to decipher developmental features of each endocrine cell, which leads to exploring efficient methods for generating surrogate β cells. We previously developed three reporter mouse lines to quantify the genesis of endocrine progenitor cells, β cells, and α cells. Flow cytometry analysis revealed a significant decrease in the number of newly-generated endocrine progenitors and β cells after birth. Based on these findings, we hypothesized that environmental changes during parturition could affect endocrine genesis. The number of newly-generated endocrine cells was quantified with the reporter mouse lines at the following stages: (i) embryonic day 19.5 (E19.5) embryos, whose parturitions were prolonged by progesterone or COX-1 inhibitor SC-560 vs. newborn pups at postnatal day 0.5 (P0.5) (both were dissected at 19.5 days after coitus), and (ii) premature pups treated with anti-progesterone drug RU-486 (both were at 18.5 days after coitus) vs. E18.5 embryos. Flow cytometry with Neurog3-Timer pancreata demonstrated that the percentage of green-fluorescent progenitors was (i) significantly higher in E19.5 embryos than in P0.5 pups (0.80% vs. 0.22%, p<0.001), and (ii) significantly lower in premature pups than in E18.5 embryos (0.66% vs. 0.93%, p=0.0018). Likewise, flow cytometry with Ins1-Timer pancreata resulted in a significant increase in β-cell genesis at E19.5 than at P0.5 (0.36% vs. 0.16%, p<0.001). Surprisingly, flow cytometry with Gcg-Timer mice resulted in (i) a significant decrease in α-cell genesis at E19.5 than at P0.5 (2.1% vs. 2.4%, p=0.035), and (ii) a significant increase in premature pups 18.5 days after coitus than in E18.5 embryos (0.77% vs. 0.58%, p=0.022), which is in contrast with the findings in Neurog3-Timer and Ins1-Timer pancreata. Thus, parturition events suppress the generation of endocrine progenitors and β cells, but not α-cell genesis, which may reflect distinct molecular mechanisms in α-cell lineage during parturition.