Loss-of-function phenotypes in S2 cells as well as other cell types in Drosophila strongly suggest that D-TPX2 only contributes a minor amount to spindle integrity and chromosome segregation compared to TPX2 in other cell types reported so far; thus, even a ‘must-be-essential’ protein could be dispensable for spindle assembly in certain cell types/organisms. This study therefore reinforces the idea that spindle assembly is driven by multiple mechanisms and the extent of usage of each mechanism varies in different cell types. It is further suggested that the presence of redundant mechanisms allows dramatic changes to the structure of a mitotic gene itself during evolution. Src is a member of the Src Family Kinases, a group of nonreceptor tyrosine kinases that share a common structure consisting of an N-terminal myristoylation site, an SH3 domain, an SH2 domain, a tyrosine kinase domain and a C-terminal negative regulatory domain. Myristoylation of the SFK protein tethers it to the inner face of the plasma membrane, whereas the SH3 and SH2 domains mediate interactions with proline-rich recognition sequences and phosphotyrosine-containing sequences, respectively. Intramolecular interactions between the SH2 and SH3 domains and their recognition sites in the SFK hold the protein in a closed, inactive conformation. Release of these intramolecular interactions by dephosphorylation of the Cterminus or by SH2 binding of another phosphotyrosine protein leads to the adoption of an open, partially active conformation. Phosphorylation of the activation loop leads to the adoption of the fully active conformation. The SFK active site is located in a cleft between the N-terminal lobe and the C-terminal lobe of the kinase domain, where substrate, ATP and Mg cations bind. Two critical elements of the active site are the DFG motif-containing activation loop and the HRD motif-containing catalytic loop. The HRD amino acids are thought to be involved in the reaction mechanism or the formation and stabilization of the active site. SFKs have been shown to be involved in regulating the actinbased microfilament cytoskeleton. The Drosophila genome contains two genes that encode SFKs: src42 and src64. Both act in the remodeling of the microfilament cytoskeleton during dorsal closure. However, in ring canal growth in the egg chamber, src64 seems to function independently of src42. Ring canals are intercellular bridges linking the nurse cells to the developing oocyte, formed from the actin-rich. Src64 is required for ring canal growth. src64 is also required for microfilament contraction during the formation of the cellular blastoderm. During early Drosophila embryogenesis, synchronized nuclear division proceeds without concomitant cell division. After nuclear division stops, a single layer of cells is formed by the simultaneous and uniform INCB28060 c-Met inhibitor invagination of plasma membrane between the peripheral nuclei. The leading edge of membrane invagination, the cellularization front, consists of stable infoldings of membrane called furrow canals surrounded by microfilaments.