Programmatic building of a secretory acinus is driven by neuronal-epithelial NRG1-ERBB3-mTORC2 signaling.

Acinar cells are the principal secretory unit of multiple exocrine organs. A single cell layered, lumenized acinus forms from a large cohort of epithelial progenitors that must initiate and coordinate three cellular programs of acinar specification, namely, lineage progression, secretion, and polarization. Despite this well-known outcome, the mechanism(s) regulating these complex programs are unknown. Here, we demonstrate that neuronal-epithelial cross-talk drives acinar specification through neuregulin (NRG1)-ERBB3-mTORC2 signaling. Using single-cell and global RNA-sequencing of developing salivary glands, we identified NRG1-ERBB3 to precisely overlap with acinar specification during gland development. Genetic deletion of Erbb3 prevented cell lineage progression and the establishment of lumenized, secretory acini. Conversely, NRG1 treatment of isolated epithelia was sufficient to recapitulate the development of secretory acini. Mechanistically, we found NRG1-ERBB3 regulates each developmental program through an mTORC2 signaling pathway. Thus, we reveal a novel neuronal-epithelial (NRG1/ERBB3/mTORC2) mechanism to orchestrate the creation of functional acini. Overall design: Comparative analysis of gene expression between 1) salivary glannds at different stages of development (E13-E18), 2) salivary epithelia treated with NRG1 for 4, 48, 72 or 96 hrs compared to corresponding controls and 3) wild type and Erbb3 deficient E16 salivary glands.

腺泡细胞是多种外分泌器官的核心分泌单位。由大量上皮祖细胞组装形成的单层管腔化腺泡，需启动并协调腺泡特化的三项核心细胞程序：谱系进展、分泌功能建立及细胞极化。尽管该发育结局已被广泛认知，但调控这些复杂程序的分子机制仍未阐明。本研究证实，神经元-上皮细胞互作可通过神经调节蛋白（neuregulin, NRG1）-ERBB3-mTORC2信号通路驱动腺泡特化。我们通过对发育中的唾液腺开展单细胞及整体RNA测序，发现NRG1-ERBB3的表达模式与腺体发育过程中的腺泡特化阶段精准对应。Erbb3基因敲除会阻断细胞谱系进展以及管腔化分泌腺泡的形成。反之，对分离培养的唾液上皮细胞施加NRG1处理，即可重现分泌型腺泡的发育过程。机制研究表明，NRG1-ERBB3通过mTORC2信号通路调控上述每一项发育程序。综上，本研究揭示了一条全新的神经元-上皮互作（NRG1/ERBB3/mTORC2）机制，可协同调控功能性腺泡的构建。整体实验设计：对以下三组样本进行基因表达谱比较分析：1）不同发育阶段（E13至E18）的唾液腺；2）经NRG1处理4、48、72或96小时的唾液上皮细胞，并设置相应对照组；3）野生型与Erbb3缺陷型E16阶段唾液腺。