PDGF-induced EGFP-actin dynamics in NIH 3T3 fibroblasts. Confocal microscopy images of stably expressed EGFP-actin were recorded every 60 seconds following PDGF treatment of serum-starved NIH 3T3 cells. Of the six cells visible in this field, one cell (upper-left) undergoes PDGF-induced aggregation of actin into discrete spots arranged as an incomplete perinuclear circle. Within minutes, each of these actin-rich sites nucleates actin tails that transiently join to form a circular actin dorsal ruffle.