Loss‐of‐function mutations in CDKL5 kinase cause severe neurodevelopmental delay and early‐onset seizures. Identification of CDKL5 substrates is key to understanding its function. Using chemical genetics, we found that CDKL5 phosphorylates three microtubule‐associated proteins: MAP1S, EB2 and ARHGEF2, and determined the phosphorylation sites. Substrate phosphorylations are greatly reduced in CDKL5 knockout mice, verifying these as physiological substrates. In CDKL5 knockout mouse neurons, dendritic microtubules have longer EB3‐labelled plus‐end growth duration and these altered dynamics are rescued by reduction of MAP1S levels through shRNA expression, indicating that CDKL5 regulates microtubule dynamics via phosphorylation of MAP1S. We show that phosphorylation by CDKL5 is required for MAP1S dissociation from microtubules. Additionally, anterograde cargo trafficking is compromised in CDKL5 knockout mouse dendrites. Finally, EB2 phosphorylation is reduced in patient‐derived human neurons. Our results reveal a novel activity‐dependent molecular pathway in dendritic microtubule regulation and suggest a pathological mechanism which may contribute to CDKL5 deficiency disorder.

Zebrafish are increasingly used in neurobiological and behavioral studies. Possible stimuli to manipulate zebrafish behavior are being investigated. The presentation of colors appears to be one of the most used approaches, but there is much debate about the exact color preference. Here we have investigated the color preference in both larvae and adult zebrafish. We have studied the effects of wavelength, contrast, intensity, and location. Furthermore, we have tried to manipulate the preference with anxiolytic drugs (ethanol and buspirone). Our results show that both adults and larvae have a clear preference for blue zones while they avoid yellow-colored zones. Red and green zones have an intermediate preference. Part of the yellow aversion is caused by a fear for this color and can be diminished by the treatment with anxiolytic drugs. The location of the color appears to be of critical importance. Presentation of the color on the walls induces an approach response whereas presentation on the bottom induces an aversion. In conclusion, colors are important stimuli to manipulate zebrafish behavior and can be used in behavioral models. Standardization of the procedures and a clear description of the used methodologies are, however, essential.