Little is known about the architecture of cellular microenvironments that support stem and precursor cells during tissue development. Although adult stem cell niches are organized by specialized supporting cells, in the developing cerebral cortex, neural stem/precursor cells reside in a neurogenic niche lacking distinct supporting cells. Here we find that neural precursors themselves comprise the niche and regulate their own development. Precursor-precursor contact regulates β-catenin signaling and cell fate. In vivo knockdown of N-cadherin reduces β-catenin signaling, migration from the niche and neuronal differentiation in vivo. N-cadherin engagement activates β-catenin signaling via Akt, suggesting a mechanism through which cells in tissues can regulate their development. These results suggest that neural precursor cell interactions can generate a self-supportive niche to regulate their own number.
It is well established that cadherin protein levels impact canonical Wnt signaling through binding and sequestering β-catenin (β-cat) from T-cell factor family transcription factors. Whether changes in intercellular adhesion can affect β-cat signaling and the mechanism through which this occurs has remained unresolved. We show that axin, APC2, GSK-3β and N-terminally phosphorylated forms of β-cat can localize to cell–cell contacts in a complex that is molecularly distinct from the cadherin–catenin adhesive complex. Nonetheless, cadherins can promote the N-terminal phosphorylation of β-cat, and cell–cell adhesion increases the turnover of cytosolic β-cat. Together, these data suggest that cadherin-based cell–cell adhesion limits Wnt signals by promoting the activity of a junction-localized β-cat phosphodestruction complex, which may be relevant to tissue morphogenesis and cell fate decisions during development.
Crayfish, bearing dangerous weapons in the form of chelae, resolve intraspecific conflicts using stereotyped behaviors and structured, escalated encounters. According to predictions of game theory models, any decision to resort to unrestrained combat without prior careful behavioral assessment of the opponent’s fighting abilities carries great risks. The present study examines the significance of internal hunger states and the presence of chemical food cues in this decision process using a 2 × 2 factorial design. Hungry crayfish escalated more rapidly, and thus took greater risks, during agonistic encounters, while the presence of a food source reduced the rate at which fights increased in intensity. However, there were no significant differences in fighting behavior as a result of the interaction between these two variables. We then address the complex trade‐offs that individuals face in fighting with respect to increased risks of injury, appetitive states, and opportunities for resource access.
The disproportional enlargement of the neocortex through evolution has been instrumental in the success of vertebrates, in particular mammals. The neocortex is a multilayered sheet of neurons generated from a simple proliferative neuroepithelium through a myriad of mechanisms with substantial evolutionary conservation. This developing neuroepithelium is populated by progenitors that can generate additional progenitors as well as post-mitotic neurons. Subtle alterations in the production of progenitors vs. differentiated cells during development can result in dramatic differences in neocortical size. This review article will examine how cadherin adhesion proteins, in particular α-catenin and N-cadherin, function in regulating the neural progenitor microenvironment, cell proliferation, and differentiation in cortical development.
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