Acts as a regulator of the microfilament network governing cellularization of the embryo. Determines the timing of a key conformational transition in the cortical microfilament network: the proper coordination of membrane invagination and basal closure of the cells. To do this, bnk possibly physically links neighboring contractile units of the early cycle 14 microfilament network in a manner that prevents basal constriction until the proper stage has been reached. Bnk together with nullo and Sry-alpha may provide auxiliary functions, by acting both to stabilize a large and dynamic microfilament structure and regulate its functions. Colocalizes with the structural transitions in the microfilament network during cellularization. Association is observed only when the network assumes an aligned and tightly apposed hexagonal configuration. Restricted to the blastoderm. Observed exclusively in the late syncytial and cellular blastoderm stages of development. Transcripts are first detected during nuclear division cycle 11. They reach a strong peak at cycle 14 and from then on gradually decline until they are no longer detectable at the end of cellularization.