Fig. 4.

Coordination of astrocyte morphological growth and refinement with synapse formation. (A) Although most neurons are made during embryonic stages, the major waves of synaptogenesis follow and depend on astrocyte production. The timing of astrocyte growth and morphological refinement overlaps significantly with this window of synaptogenesis. (B) Astrocytes initially extend large, filopodial processes that overlap significantly with neighboring astrocytes; however, by postnatal day 21, astrocytes refine their morphology to occupy unique spatial domains and elaborate fine processes that closely associate with synapses. (C) A complex interrelation exists between synapses and astrocyte processes. Eph or ephrin signaling can bidirectionally control astrocyte features, as well as spine morphology (see text).