Salinno, C. | Search bioRxiv

bioRxiv2021

Synaptotagmin 13 orchestrates pancreatic endocrine cell egression and islet morphogenesis

Epithelial cell egression is important for organ development, but also drives cancer metastasis. Better understandings of pancreatic epithelial morphogenetic programs generating islets of Langerhans aid to diabetes therapy. Here we identify the Ca2+-independent atypical Synaptotagmin 13 (Syt13) as a key driver of endocrine cell egression and islet formation. We detected upregulation of Syt13 in endocrine precursors that correlates with increased expression of unique cytoskeletal components. High-resolution imaging reveals a previously unidentified apical-basal to front-rear repolarization during endocrine cell egression. Strikingly, Syt13 interacts with acetylated tubulin and phosphatidylinositol phospholipids and localizes to the leading-edge of egressing cells. Knockout of Syt13 impairs endocrine cell egression and skews the - to-{beta}-cell ratio. Mechanistically, Syt13 regulates endocytosis to remodel the basement membrane and cell-matrix adhesion at the leading-edge of egressing endocrine cells. Altogether, these findings implicate an unexpected role of Syt13 in regulating cell polarity to orchestrate endocrine cell egression and islet morphogenesis.

developmental biology↗

bioRxiv2021

Generation of a novel Nkx6-1 Venus fusion reporter mouse line

Nkx6-1 is a member of the Nkx family of homeodomain transcription factors (TF) that regulates motor neuron development, neuron specification and pancreatic endocrine and {beta}-cell differentiation. To facilitate the isolation and tracking of Nkx6-1-expressing cells, we have generated a novel Nkx6-1 Venus Fusion (Nkx6-1-VF) reporter allele. The Nkx6-1-VF knock-in reporter is regulated by endogenous cis-regulatory elements of Nkx6-1 and the fluorescent protein fusion does not interfere with the TF function, as homozygous mice are viable and fertile. In addition, the nuclear localization of Nkx6-1-VF protein reflects the endogenous Nkx6-1 protein distribution. During embryonic pancreas development, the reporter protein marks the pancreatic ductal progenitors and the endocrine lineage, but is absent in the exocrine compartment. Moreover, the levels of Nkx6-1-VF reporter is upregulated upon {beta}-cell differentiation during the major wave of endocrinogenesis. In the adult islets of Langerhans, the reporter protein is exclusively found in insulin-secreting {beta}-cells. Importantly, the Venus reporter activities allows successful tracking of {beta}-cells in live-cell imaging and their specific isolation by flow sorting. In summary, the generation of Nkx6-1-VF reporter line provides a unique tool to study the spatio-temporal expression pattern of this TF during organ development and isolate and track Nkx6-1-expressing cells such as pancreatic {beta}-cells, but also neurons and motor neurons in health and disease.

developmental biology↗