Linking Maternal Problematic Smartphone Use to Maternal Hostility and Warmth Toward Children: A Daily Diary Study of Chinese Families.

Astrocytes perform vital roles across the lifespan of a synapse, from synapse formation to synaptic transmission, to synapse elimination (reviewed in ; ; ; ; ; ). Indeed, at least a subset of synapses physically interacts with astrocytes to form ‘tripartite synapses’. The abundance for such astrocyte–synapse contacts varies among synapse types from <25% of synapses to nearly all synapses (; ; ; ; ; ). Some synapses are always associated with astrocytic processes (e.g., parallel-fiber synapses in the cerebellum; ; ), whereas others are never associated with astrocytes (e.g., calyx synapses in the brainstem; ), and most are in between these two extremes. The emergence of novel tools to genetically access and interrogate astrocytes has paved the way for a new effort dedicated to understanding the functional significance and the molecular mechanisms of the synaptic roles of astrocytes (; ; ; ). Among others, RNA sequencing (RNAseq) studies have revealed astrocytic expression of cell-adhesion molecules that were traditionally viewed as specifically synaptic in nature (; ; ; ; ; ; ). The astrocytic expression of these synaptic cell-adhesion molecules gave rise to a parsimonious and attractive hypothesis that accounts for how astrocytes may interact with synapses at the molecular level (; ; ; ; ; ). This hypothesis posits that astrocytes are integrated into tripartite synapses via synaptic cell-adhesion molecules, thereby enabling astrocytes to regulate synapse formation, maturation, function, or elimination. Prominent among synaptic cell-adhesion molecules that are expressed by astrocytes are neuroligins, a family of postsynaptic adhesion molecules that are encoded in vertebrates by four genes () (see ). The four neuroligin genes produce highly homologous proteins with an identical domain structure and a high degree of sequence similarity (; ; ). Neuroligins were discovered as the postsynaptic ligands for presynaptic neurexins but also bind to presynaptic LAR-type receptor tyrosine phosphatases and postsynaptic MDGA proteins (; ; ; ; ; ; ). Despite their similarity, however, different neuroligins display distinct localizations in the brain and perform different non-redundant functions (; ). Specifically, neuronal and function exclusively at excitatory and inhibitory synapses, respectively, whereas and Nlgn4 may act at both excitatory and inhibitory synapses (; ; ; ; ; ; ; ; ; ; ; ).