CaMK-II activation is essential for zebrafish inner ear development and acts through Delta–Notch signaling

Abstract

Zebrafish inner ear development is characterized by the crystallization of otoliths onto immotile kinocilia that protrude from sensory "hair" cells. The stereotypical formation of these sensory structures is dependent on the expression of key patterning genes and on Ca2+ signals. One potential target of Ca2+ signaling in the inner ear is the type II Ca2+/calmodulin-dependent protein kinase (CaMK-II), which is preferentially activated in hair cells, with intense activation at the base of kinocilia. In zebrafish, CaMK-II is encoded by seven genes; the expression of one of these genes (camk2g1) is enriched in hair cells. The suppression of camk2g1 expression by antisense morpholino oligonucleotides or inhibition of CaMK-II activation by the pharmacological antagonist, KN-93, results in aberrant otolith formation without preventing cilia formation. In fact, CaMK-II suppression results in additional ciliated hair cells and altered levels of Delta-Notch signaling members. DeltaA and deltaD transcripts are increased and DeltaD protein accumulates in hair cells of CaMK-II morphants, indicative of defective recycling and/or exocytosis. Our findings indicate that CaMK-II plays a critical role in the developing ear, influencing cell differentiation through extranuclear effects on Delta-Notch signaling. Continued expression and activation of CaMK-II in maculae and cristae in older embryos suggests continued roles in auditory sensory maturation and transduction.

Germ cell differentiation requires Tdrd7-dependent chromatin and transcriptome reprogramming marked by germ plasm relocalization

“…Hence, we performed differential gene expression analysis of isolated germ-plasmcarrying cells and somatic cells at each stage spanning ZGA period and found several differentially regulated genes (Figure 3A). This analysis revealed that, before ZGA, already 23 genes were differentially expressed between the two cell types (FDR < 0.1) ( Table S2), confirming that maternal mRNAs are selectively retained in PGCs as shown previously (Eno et al, 2018;Gazdag et al, 2009;Gerovska and Araú zo-Bravo, 2016;Gorokhova et al, 2007;Levine et al, 2000;Rothschild et al, 2013). However, it is noteworthy that 12 out of 23 identified transcripts have not yet been associated with germ cell or PGC functions and are candidates for novel maternal germ plasm transcripts.…”

Essentiality of Regulator of G Protein Signaling 6 and Oxidized Ca 2+ /Calmodulin‐Dependent Protein Kinase II in Notch Signaling and Cardiovascular Development

“…The precise nature of the pathway by which ox‐CaMKII cooperates with RGS6 to ensure proper Notch signaling is not yet clear. Among numerous possible mechanisms is the potential role of ox‐CaMKII in trafficking/recycling of Notch ligands, as observed in zebrafish inner ear, or in phosphorylation‐mediated degradation of a Notch co‐repressor (silencing mediator of retinoic acid and thyroid hormone receptor), the only known links between activated (phosphorylated) CaMKII and Notch signaling. Importantly, the knock‐in MM to VV mutation eliminates ROS‐mediated activation, but does not interfere with CaMKII autophosphorylation …”

Cilia in the developing zebrafish ear

“…The active phosphorylated form of type II calcium/calmodulin kinase CaMK-II is expressed in the zebrafish ear in hair cell kinocilia, most strongly at their base, where it may localise to the ciliary transition zone and/or stereociliary bundle (Rothschild et al, 2013). Interestingly, disruption of CaMK-II activity-either pharmacologically, or via morpholino-mediated knockdown of camk2g1-results in a disruption of Delta-Notch signalling, and the development of supernumerary tether cells.…”