Cadherin-7 mediates proper neural crest cell-placodal neuron interactions during trigeminal ganglion assembly.

The cranial trigeminal ganglia play a vital role in the peripheral nervous system through their relay of sensory information from the vertebrate head to the brain. These ganglia are generated from the intermixing and coalescence of two distinct cell populations: cranial neural crest cells and placodal neurons. Trigeminal ganglion assembly requires the formation of cadherin-based adherens junctions within the neural crest cell and placodal neuron populations; however, the molecular composition of these adherens junctions is still unknown. Herein, we aimed to define the spatio-temporal expression pattern and function of Cadherin-7 during early chick trigeminal ganglion formation. Our data reveal that Cadherin-7 is expressed exclusively in migratory cranial neural crest cells and is absent from trigeminal neurons. Using molecular perturbation experiments, we demonstrate that modulation of Cadherin-7 in neural crest cells influences trigeminal ganglion assembly, including the organization of neural crest cells and placodal neurons within the ganglionic anlage. Moreover, alterations in Cadherin-7 levels lead to changes in the morphology of trigeminal neurons. Taken together, these findings provide additional insight into the role of cadherin-based adhesion in trigeminal ganglion formation, and, more broadly, the molecular mechanisms that orchestrate the cellular interactions essential for cranial gangliogenesis.

Migratory neural crest cell αN-catenin impacts chick trigeminal ganglia formation.

Neural crest cells are an embryonic cell population that is crucial for proper vertebrate development. Initially localized to the dorsal neural folds, premigratory neural crest cells undergo an epithelial-to-mesenchymal transition (EMT) and migrate to their final destinations in the developing embryo. Together with epidermally-derived placode cells, neural crest cells then form the cranial sensory ganglia of the peripheral nervous system. Our prior work has shown that αN-catenin, the neural subtype of the adherens junction α-catenin protein, regulates cranial neural crest cell EMT by controlling premigratory neural crest cell cadherin levels. Although αN-catenin down-regulation is critical for initial neural crest cell EMT, a potential role for αN-catenin in later neural crest cell migration, and formation of the cranial ganglia, has not been examined. In this study, we show for the first time that migratory neural crest cells that will give rise to the cranial trigeminal ganglia express αN-catenin and Cadherin-7. αN-catenin loss- and gain-of-function experiments reveal effects on the migratory neural crest cell population that include subsequent defects in trigeminal ganglia assembly. Moreover, αN-catenin perturbation in neural crest cells impacts the placode cell contribution to the trigeminal ganglia and also changes neural crest cell Cadherin-7 levels and localization. Together, these results highlight a novel function for αN-catenin in migratory neural crest cells that form the trigeminal ganglia.

The tight junction scaffolding protein cingulin regulates neural crest cell migration.

Neural crest cells give rise to a diverse range of structures during vertebrate development. These cells initially exist in the dorsal neuroepithelium and subsequently acquire the capacity to migrate. Although studies have documented the importance of adherens junctions in regulating neural crest cell migration, little attention has been paid to tight junctions during this process. We now identify the tight junction protein cingulin as a key regulator of neural crest migration. Cingulin knock-down increases the migratory neural crest cell domain, which is correlated with a disruption of the neural tube basal lamina. Overexpression of cingulin also augments neural crest cell migration and is associated with similar basal lamina changes and an expansion of the premigratory neural crest population. Cingulin overexpression causes aberrant ventrolateral neuroepithelial cell delamination, which is linked to laminin loss and a decrease in RhoA. Together, our results highlight a novel function for cingulin in the neural crest.

Neural crest cell-placodal neuron interactions are mediated by Cadherin-7 and N-cadherin during early chick trigeminal ganglion assembly.

Background: Arising at distinct positions in the head, the cranial ganglia are crucial for integrating various sensory inputs. The largest of these ganglia is the trigeminal ganglion, which relays pain, touch and temperature information through its three primary nerve branches to the central nervous system. The trigeminal ganglion and its nerves are composed of derivatives of two critical embryonic cell types, neural crest cells and placode cells, that migrate from different anatomical locations, coalesce together, and differentiate to form trigeminal sensory neurons and supporting glia. While the dual cellular origin of the trigeminal ganglion has been known for over 60 years, molecules expressed by neural crest cells and placode cells that regulate initial ganglion assembly remain obscure. Prior studies revealed the importance of cell surface cadherin proteins during early trigeminal gangliogenesis, with Cadherin-7 and neural cadherin (N-cadherin) expressed in neural crest cells and placode cells, respectively. Although cadherins typically interact in a homophilic ( i.e., like) fashion, the presence of different cadherins expressed in neural crest cells and placode cells raises the question as to whether heterophilic cadherin interactions may also be occurring. Given this, the aim of the study was to understand whether Cadherin-7 and N-cadherin were interacting during initial trigeminal ganglion formation. Methods: To assess potential interactions between Cadherin-7 and N-cadherin, we used biochemistry and innovative imaging assays conducted in vitro and in vivo, including in the forming chick trigeminal ganglion. Results: Our data revealed a physical interaction between Cadherin-7 and N-cadherin. Conclusions: These studies identify a new molecular basis by which neural crest cells and placode cells can aggregate in vivo to build the trigeminal ganglion during embryogenesis.

Annexin a6 modulates chick cranial neural crest cell emigration.

The vertebrate neural crest is a population of migratory cells that originates in the dorsal aspect of the embryonic neural tube. These cells undergo an epithelial-to-mesenchymal transition (EMT), delaminate from the neural tube and migrate extensively to generate an array of differentiated cell types. Elucidating the gene regulatory networks involved in neural crest cell induction, migration and differentiation are thus crucial to understanding vertebrate development. To this end, we have identified Annexin A6 as an important regulator of chick midbrain neural crest cell emigration. Annexin proteins comprise a family of calcium-dependent, membrane-binding molecules that mediate a variety of cellular and physiological processes including cell adhesion, migration and invasion. Our data indicate that Annexin A6 is expressed in the proper spatio-temporal pattern in the chick midbrain to play a potential role in neural crest cell ontogeny. To investigate Annexin A6 function, we have depleted or overexpressed Annexin A6 in the developing midbrain neural crest cell population. Our results show that knock-down or overexpression of Annexin A6 reduces or expands the migratory neural crest cell domain, respectively. Importantly, this phenotype is not due to any change in cell proliferation or cell death but can be correlated with changes in the size of the premigratory neural crest cell population and with markers associated with EMT. Taken together, our data indicate that Annexin A6 plays a pivotal role in modulating the formation of cranial migratory neural crest cells during vertebrate development.