AI Summary
EHBP1 is a protein involved in the development of dendritic arbors in neurons. It interacts with another protein called syndapin I, and this interaction is critical for the function of EHBP1 in neuromorphogenesis. EHBP1's role in dendritic arbor formation does not require its binding to Rab GTPases, but it does depend on its binding to syndapin I. The presence of syndapin I in developing neurons and its overlapping dynamics with EHBP1 further support this finding. Two additional domains of EHBP1, the C2 and CH domains, are also necessary for dendritic arborization. In addition, the actin nucleator protein Cobl is involved in EHBP1's function, suggesting that actin nucleation plays a role in dendritic arbor formation. EHBP1, syndapin I, and Cobl form protein complexes that are necessary for proper cell shape during neuronal development.
The coordinated action of a plethora of factors is required for the organization and dynamics of membranous structures critically underlying the development and function of cells, organs, and organisms. The evolutionary acquisition of additional amino acid motifs allows for expansion and/or specification of protein functions. We identify a thus far unrecognized motif specific for chordata EHBP1 proteins and demonstrate that this motif is critically required for interaction with syndapin I, an F-BAR domain-containing, membrane-shaping protein predominantly expressed in neurons. Gain-of-function and loss-of-function studies in rat primary hippocampal neurons (of mixed sexes) unraveled that EHBP1 has an important role in neuromorphogenesis. Surprisingly, our analyses uncovered that this newly identified function of EHBP1 did not require the domain responsible for Rab GTPase binding but was strictly dependent on EHBP1’s syndapin I binding interface and on the presence of syndapin I in the developing neurons. These findings were underscored by temporally and spatially remarkable overlapping dynamics of EHBP1 and syndapin I at nascent dendritic branch sites. In addition, rescue experiments demonstrated the necessity of two additional EHBP1 domains for dendritic arborization, the C2 and CH domains. Importantly, the additionally uncovered critical involvement of the actin nucleator Cobl in EHBP1 functions suggested that not only static association with F-actin via EHBP1’s CH domain is important for dendritic arbor formation but also actin nucleation. Syndapin interactions organize ternary protein complexes composed of EHBP1, syndapin I, and Cobl, and our functional data show that only together these factors give rise to proper cell shape during neuronal development.