Functional Role of SIL1 in Neurodevelopment and Learning

Reelin Regulates Developmental Desynchronization Transition of Neocortical Network Activity

During the first and second stages of postnatal development, neocortical neurons exhibit a wide range of spontaneous synchronous activity (SSA). Towards the end of the second postnatal week, the SSA is replaced by a more sparse and desynchronized firing pattern. The developmental desynchronization of neocortical spontaneous neuronal activity is thought to be intrinsically generated, since sensory deprivation from the periphery does not affect the time course of this transition. The extracellular protein reelin controls various aspects of neuronal development through multimodular signaling. However, so far it is unclear whether reelin contributes to the developmental desynchronization transition of neocortical neurons. The present study aims to investigate the role of reelin in postnatal cortical developmental desynchronization using a conditional reelin knockout (RelncKO) mouse model. Conditional reelin deficiency was induced during early postnatal development, and Ca2+ recordings were conducted from organotypic cultures (OTCs) of the somatosensory cortex. Our results show that both wild type (wt) and RelncKO exhibited an SSA pattern during the early postnatal week. However, at the end of the second postnatal week, wt OTCs underwent a transition to a desynchronized network activity pattern, while RelncKO activity remained synchronous. This changing activity pattern suggests that reelin is involved in regulating the developmental desynchronization of cortical neuronal network activity. Moreover, the developmental desynchronization impairment observed in RelncKO was rescued when RelncKO OTCs were co-cultured with wt OTCs. Finally, we show that the developmental transition to a desynchronized state at the end of the second postnatal week is not dependent on glutamatergic signaling. Instead, the transition is dependent on GABAAR and GABABR signaling. The results suggest that reelin controls developmental desynchronization through GABAAR and GABABR signaling.

Reelin functions beyond neuronal migration: from synaptogenesis to network activity modulation

Reelin, a glycoprotein of the extracellular matrix, has been the focus of several studies over the years, mostly for its role in cell migration. Here we report the role of this molecule and of its downstream pathways in post-mitotic neurons and how they contribute to neural circuit assembly, refinement and function. Accumulating evidence has pointed at a major role for Reelin in axonal guidance, synaptogenesis and dendritic spine formation. In particular, new evidence points at a direct role in axonal targeting and refinement at the target site. In addition, recent advances highlight new functions of Reelin in the modulation of synaptic activity, plasticity and behavior and in the direct regulation of GABA receptors expression and stability. We discuss these findings in the context of neurodevelopmental disorders.