Wnt signaling plays critical roles in dorsoventral fate specification and anteroposterior patterning, as well as in morphogenetic cell movements. Dishevelled proteins, or Dvls, mediate the activation of Wnt/ß-catenin and Wnt/planar cell polarity pathways. There are at least three highly conserved Dvl proteins in vertebrates, but the implication of each Dvl in key early developmental processes remains poorly understood. In this study, we use genome-editing approach to generate different combinations of maternal and zygotic dvl mutants in zebrafish, and examine their functions during early development. Maternal transcripts for dvl2 and dvl3a are most abundantly expressed, whereas the transcript levels of other dvl genes are negligible. Phenotypic and molecular analyses show that early dorsal fate specification is not affected in maternal and zygotic dvl2 and dvl3a double mutants, suggesting that the two proteins may be dispensable for the activation of maternal Wnt/ß-catenin signaling. Interestingly, convergence and extension movements and anteroposterior patterning require both maternal and the zygotic functions of Dvl2 and Dvl3a, but these processes are more sensitive to Dvl2 dosage. Zygotic dvl2 and dvl3a double mutants display mild axis extension defect with correct anteroposterior patterning. However, maternal and zygotic double mutants exhibit most strongly impaired convergence and extension movements, severe trunk and posterior deficiencies, and frequent occurrence of cyclopia and craniofacial defects. Our results suggest that Dvl2 and Dvl3a products are required for the activation of zygotic Wnt/ß-catenin signaling and Wnt/planar cell polarity pathway, and regulate zygotic developmental processes in a dosage-dependent manner. This work provides insight into the mechanisms of Dvl-mediated Wnt signaling pathways during early vertebrate development. The embryogenesis of most animals is first supported by maternal gene products accumulated in the oocyte, and then by the expression of genes from the zygote. In all vertebrates, there are at least three Dishevelled (Dvl) proteins, which play critical roles in normal development and human diseases. They are both maternally and zygotically expressed, and can activate the ß-catenin-dependent Wnt pathway that regulates gene expression and cell fate, and the ß-catenin-independent Wnt pathway that orchestrates cell movements. In zebrafish embryo, Dvl2 and Dvl3a are most abundant, but their functions are not fully understood. We find that maternally and zygotically expressed Dvl2 plays a predominant role in the elongation of the anteroposterior axis, and the expression of genes involved in the development of the posterior region. Dvl3a cooperates with Dvl2 in these processes. Analyses after loss-of-function of these genes indicate that deficiency of maternal and zygotic Dvl2 and Dvl3a results in embryos with cyclopia, craniofacial defects, and severe abnormality in the trunk and posterior regions. Many human birth defects and other diseases, like cancer, are attributed to the dysfunction of the Wnt pathways. Our results help to understand the mechanisms of Dvl-mediated Wnt pathway activation, and the causes of developmental disorders.

RNA-binding proteins (RBPs) regulate gene expression at the post-transcriptional level. They play major roles in the tissue- and stage-specific expression of protein isoforms as well as in the maintenance of protein homeostasis. The inner ear is a bi-functional organ, with the cochlea and the vestibular system required for hearing and for maintaining balance, respectively. It is relatively well documented that transcription factors and signaling pathways are critically involved in the formation of inner ear structures and in the development of hair cells. Accumulating evidence highlights emerging functions of RBPs in the post-transcriptional regulation of inner ear development and hair cell function. Importantly, mutations of splicing factors of the RBP family and defective alternative splicing, which result in inappropriate expression of protein isoforms, lead to deafness in both animal models and humans. Because RBPs are critical regulators of cell proliferation and differentiation, they present the potential to promote hair cell regeneration following noise- or ototoxin-induced damage through mitotic and non-mitotic mechanisms. Therefore, deciphering RBP-regulated events during inner ear development and hair cell regeneration can help define therapeutic strategies for treatment of hearing loss. In this review, we outline our evolving understanding of the implications of RBPs in hair cell formation and hearing disease with the aim of promoting future research in this field.

Cell adhesion and polarized cellular behaviors play critical roles in a wide variety of morphogenetic events. In the zebrafish embryo, epiboly represents an important process of epithelial morphogenesis that involves differential cell adhesion and dynamic cell shape changes for coordinated movements of different cell populations, but the underlying mechanism remains poorly understood. The adaptor protein Lurap1 functions to link myotonic dystrophy kinase-related Rac/Cdc42-binding kinase with MYO18A for actomyosin retrograde flow in cell migration. We previously reported that it interacts with Dishevelled in convergence and extension movements during gastrulation. Here, we show that it regulates blastoderm cell adhesion and radial cell intercalation during epiboly. In zebrafish mutant embryos with loss of both maternal and zygotic Lurap1 function, deep cell multilayer of the blastoderm exhibit delayed epiboly with respect to the superficial layer. Time-lapse imaging reveals that these deep cells undergo unstable intercalation, which impedes their expansion over the yolk cell. Cell sorting and adhesion assays indicate reduced cellular cohesion of the blastoderm. These defects are correlated with disrupted cytoskeletal organization in the cortex of blastoderm cells. Thus, the present results extend our previous works by demonstrating that Lurap1 is required for cell adhesion and cell behavior changes to coordinate cell movements during epithelial morphogenesis. They provide insights for a further understanding of the regulation of cytoskeletal organization during gastrulation cell movements.