TAOK1 is associated with neurodevelopmental disorder and essential for neuronal maturation and cortical development

Abstract

Thousand and one amino-acid kinase 1 (TAOK1) is a MAP3K protein kinase, regulating different mitogen-activated protein kinase pathways, thereby modulating a multitude of processes in the cell. Given the recent finding of TAOK1 involvement in neurodevelopmental disorders (NDDs), we investigated the role of TAOK1 in neuronal function and collected a cohort of 23 individuals with mostly de novo variants in TAOK1 to further define the associated NDD. Here, we provide evidence for an important role for TAOK1 in neuronal function, showing that altered TAOK1 expression levels in the embryonic mouse brain affect neural migration in vivo, as well as neuronal maturation in vitro. The molecular spectrum of the identified TAOK1 variants comprises largely truncating and nonsense variants, but also missense variants, for which we provide evidence that they can have a loss of function or dominant-negative effect on TAOK1, expanding the potential underlying causative mechanisms resulting in NDD. Taken together, our data indicate that TAOK1 activity needs to be properly controlled for normal neuronal function and that TAOK1 dysregulation leads to a neurodevelopmental disorder mainly comprising similar facial features, developmental delay/intellectual disability and/or variable learning or behavioral problems, muscular hypotonia, infant feeding difficulties, and growth problems.

Keywords: TAOK1; cortical development; functional genomics; in utero electroporation; neurodevelopmental disorders.

Figure 1

Knockdown of Taok1 by in utero electroporation at embryonic day 14.5 results in a severe migration deficit. (a) Representative images from postnatal day 1 brain, showing the transfected cells (mRFP+) from the subventricular zone (SVZ; indicated by the arrow) to the cortical plate (CP; indicated by the arrowheads). (b) Cumulative distribution of the transfected neurons at P1 from the cortical plate (CP) to the intermediate zone (IZ). Inset, percentage of neurons reaching the superficial layers of the cortex (sum of bins 1 through 4). (c) Representative images from postnatal Day 7 brains, showing the transfected cells (mRFP+) from the SVZ to the cerebral cortex layer 2/3 (indicated by the arrowheads). (d) Cumulative distribution of the transfected neurons from layer 2/3 to the IZ. Inset, percentage of neurons reaching layer 2/3 of the cortex (sum of bins 2–4). Data are presented as mean ± SEM. Numbers between brackets indicate the number of images analyzed for each condition. TAOK1, thousand and one amino‐acid kinase 1; SEM, standard error of the means. ***p < .001

Figure 2

Facial features of patients with de novo variants in thousand and one amino‐acid kinase 1 (TAOK1) and schematic overview of TAOK1 showing the location of the variants. (a) Facial profiles of seven unrelated patients and their facial composite created by the research tool of the Face2Gene application (FDNA Inc.), using the DeepGestalt algorithm (Gurovich et al., 2019). The facial features suggestive for the TAOK1‐associated disorder include high forehead/frontal bossing (individuals 4, 5, 6, 7, and 12), downslanting palpebral fissures (individuals 3, 4, 5, 14, and 16), long and/or pronounced philtrum, small chin (6, 7, and 12) and a bulbous nose (individuals 4, 5, 6, 7, and 12). (b) Schematic overview of the protein domain organization (top) and the corresponding messenger RNA structure (bottom) of TAOK1, with on top in gray the localization of the variants found previously (Dulovic‐Mahlow et al., 2019), and below in black the localization of the novel variants identified here. (c) Structure of the TAOK1 protein from the N‐terminal to amino acid 870, showing the localization of four of the missense variants (TAOK1^Arg150Ile, TAOK1^Leu167Arg, TAOK1^Met231Val, TAOK1^Leu315Phe, and TAOK1^Leu548Pro) identified here

Figure 3

Differential effect of TAOK1 variants on protein expression and neuronal development in vitro. (a) Western blot analysis revealing altered expression levels of some TAOK1 variants compared to TAOK1^WT when overexpressed in HEK‐293T cells. The number of samples is indicated between brackets for each condition. (b) Representative confocal images of hippocampal neurons transfected with empty vector (EV), TAOK1^WT, or TAOK1 variants, showing clear overexpression of the TAOK1 protein upon staining for TAOK1 for each TAOK1 condition. (c) Total neurite length and arborization normalized to control. Data are presented as mean ± SEM. The number of independently analyzed culture wells/cells is indicated between brackets for each condition. TAOK1, thousand and one amino‐acid kinase 1; WT, wild‐type. *Compared to empty vector condition and ^#compared to TAOK1^WT condition. **p< .01, ***p< .001, and ^### p< .001

Figure 4

Differential effect of thousand and one amino‐acid kinase 1 (TAOK1) variants on neuronal migration in vivo. (a) Representative images from postnatal Day 1 brain, showing the transfected cells (tdTomato+) from the subventricular zone (SVZ; indicated by the arrow) to the cortical plate (CP; indicated by the arrowheads). (b) Cumulative distribution of the transfected neurons at P1 from the CP to the intermediate zone (IZ). (c) Percentage of neurons reaching the superficial layers of the cortex (sum of bins 1–4). Data are presented as mean ± SEM. Number of images analyzed is indicated for each condition. *Compared to empty vector condition and ^#compared to TAOK1^WT condition. *p < .05, **p < .01, ***p < .001, ^## p < .01, and ^### p < .001