Fig. 9. Model for src64-dependent and src64-independent forces acting during cellularization. (A) Epistasis pathway for microfilament contraction during cellularization. src64 is epistatic to bnk in the pathway controlling microfilament ring contraction. tec29 is speculatively placed in the pathway with src64 as Tec kinases are generally activated by Src kinases, although this has not been experimentally confirmed for Drosophila cellularization. scraps (anillin) has been placed in a parallel pathway to bnk and src64 because it plays an important, but indirect, role in microfilament ring contraction by stabilizing microfilament rings. In the absence of anillin, microfilament rings are not formed, but the disorganized microfilaments still have the ability to contract in the absence of bnk activity. peanut (pnut) also acts in this process. (B) Mechanical model for the interaction of Bnk and Src64 protein during early cellularization. See Discussion for details. (C) Mechanical model for the interaction of Bnk and Src64 protein during late cellularization. See Discussion for details.