Editors' ChoiceDevelopment

Tubing with VIP

Sci. Signal.  02 Sep 2014:
Vol. 7, Issue 341, pp. ec236
DOI: 10.1126/scisignal.2005856

Organs are complex structures composed of different kinds of cells and tissues that must develop in a coordinated manner. Although instructive signals from developing organs to the innervating neurons are well known, how innervating neurons contribute to the development of their targets is less studied. Nedvetsky et al. examined the development of the mouse submandibular salivary gland (SMG), which is innervated by parasympathetic nerves emanating from the parasympathetic submandibular ganglion (PSG). Previous work showed that acetylcholine released from the PSG neurons mediated the maintenance of a population of progenitor cells required for the development of full-sized SMG (see Houtz and Kuruvilla). Here, vasoactive intestinal peptide (VIP), another signaling molecule released from PSG neurons, was determined to play a role in SMG development. Ex vivo cultures of embryonic SMG, which include the innervating neurons, exposed to an inhibitor of the neurotrophic factor neurturin exhibited shortened nerves, impaired innervation, reduced epithelial branching, and impaired duct formation. Whereas inhibition of muscarinic acetylcholine signaling resulted in smaller SMGs with reduced epithelial branching, duct width and midline accumulation of duct precursors appeared unaffected. In contrast, inhibition of VIP signaling with a VIP receptor 1 (VIPR1) antagonist resulted in reduced epithelial branching with disrupted condensation of the ductal precursors at the midline and increased duct width. Exposure of PSG to neurturin stimulated the expression of the gene encoding VIP, and transcriptional microarray analysis showed that VIP expression increased at the time of secondary duct formation and lumenization. VIP was enriched in the PSG and absent from the SMG epithelia; VIPR1 was primarily present in the SMG epithelia. When cocultured with PSG in the presence of neurturin, rudimentary SMG epithelial cultures (lacking mesenchymal cells or nerves) exhibited increased branching and ductal length, the latter of which was blocked by inhibition of VIPR1 and was mimicked by exposing the cultures to VIP in the absence of PSG. Furthermore, culturing the rudimentary epithelia in the presence of VIP enabled the formation of a continuous ductal lumen, which was dependent on protein kinase A (PKA) activity; without VIP, the epithelia formed small, discontinuous microlumens. VIP stimulated the production of adenosine 3′,5′-monophosphate (cAMP) and phosphorylation of a PKA target in the rudimentary epithelial cultures, and pharmacological analysis with specific agonists or antagonists of cAMP effectors showed that PKA was important for ductal elongation in the rudimentary epithelial cultures and for lumen formation in the ex vivo cultured SMG. Fluid flow can stimulate lumen expansion, and the Cl-conducting cystic fibrosis transmembrane conductance regulator (CFTR) stimulates fluid flow and is activated by VIP. Inhibition of CFTR blocked VIP-induced lumen expansion in the epithelial cultures. In vivo inhibition of VIPR1 during the period of SMG development resulted in narrower lumen, and CFTR-null mice had SMGs with abnormal duct morphology. Thus, this provides another example showing that signaling in both directions, from the tissue to the nerves and from the nerves to the tissue, is needed for proper organogenesis.

P. I. Nedvetsky, E. Emmerson, J. K. Finley, A. Ettinger, N. Cruz-Pacheco, J. Prochazka, C. L. Haddox, E. Northrup, C. Hodges, K. E. Mostov, M. P. Hoffman, S. M. Knox, Parasympathetic innervation regulates tubulogenesis in the developing salivary gland. Dev. Cell 30, 449–462 (2014). [PubMed]

J. Houtz, R. Kuruvilla, VIP pipes up: Neuronal signals direct tubulogenesis. Dev. Cell 30, 361–362 (2014). [PubMed]