Effects of Lat A and Arp3 RNAi on nascent cap F-actin. (A) Co-expressed PIP₂ and F-actin probes at telophase 11 following control (DMSO) or Lat A injection. Corner brackets show similar nascent caps at 0 s. Arrows point to aggregated nascent cap PM in response to Lat A. The Lat A-induced PM aggregation coincided with F-actin loss (27–108 s). In control injections, the nascent cap PM domain expanded and increased in F-actin (26–104 s). Seen in 5/5 embryos for both control and Lat A injections. (B) F-actin probe with control or Arp3 RNAi. Corner brackets show planes of nascent cap folds (0 µm) and tubules (−0.9 µm) with lower F-actin in Arp3 RNAi. Arrows show F-actin at pseudocleavage furrows in control. F-actin-positive pseudocleavage furrows are minimal in Arp3 RNAi. Seen in 10/12 Arp3 RNAi embryos and 10/10 control RNAi embryos.