Role of DENN Domain-Containing Protein 5b (dennd5b) during early embryonic development of zebrafish.

Prior studies on non-canonical Wnt signaling have established Dishevelled Associated Activator of Morphogenesis 1 (Daam1) as a crucial link in cell movements by cytoskeletal rearrangement. Overexpression or depletion of Daam1 blocks gastrulation in Xenopus embryos and results in phenotype characteristic of spina bifida. A yeast two-hybrid screen has been performed to further identify factors required downstream of Daam1. Among many, DENN (Differentially Expressed in Normal versus Neoplastic cells) domain-containing protein 5 (Dennd5A) is identified as a binding partner of Daam1. In zebrafish, dennd5a and dennd5b are human orthologues of DENND5A and DENND5B. Until now, no data on zebrafish dennd5b's expression or function is available. This current study elucidates the expression and function of the dennd5b during the early embryonic development of zebrafish. dennd5b shows 68.18% sequence similarity with human DENND5B and 68.56% with zebrafish dennd5a. Semi-quantitative RT-PCR showed maternal deposition of dennd5b at 0 h post-fertilization (hpf), continued expression through gastrulation, somite formation, and persistence into the larval stage. Spatial analysis demonstrated ubiquitous expression during cleavage and gastrulation, followed by restriction to the brain and neural tube during early somite stages, with brain-specific expression maintained through late embryogenesis and larval stage. Functional studies of dennd5b revealed compressed head and tail deformity. Both loss-of-function and gain-of-function perturbations disrupted convergence and extension movements, affecting rhombomere patterning, neural plate morphology, somite organization, notochord structure, and prechordal plate formation. Together, these findings establish dennd5b as essential for zebrafish embryogenesis, particularly in neural development, highlighting a conserved role downstream of Daam1 in non-canonical Wnt-mediated morphogenesis.