X-linked intellectual disability gene CASK regulates postnatal brain growth in a non-cell autonomous manner.

Sarika Srivastava,Konark Mukherjee,Helen Clark,Haiyan Zhang,Jeffery Willis,Matthew Hulver,Chen Liang,Ryan Mcmillan,Vrushali Chavan

doi:10.1186/s40478-016-0295-6

Sarika Srivastava, Konark Mukherjee + Show 7 more

Open Access

https://doi.org/10.1186/s40478-016-0295-6

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Abstract

The phenotypic spectrum among girls with heterozygous mutations in the X-linked intellectual disability (XLID) gene CASK (calcium/calmodulin-dependent serine protein kinase) includes postnatal microcephaly, ponto-cerebellar hypoplasia, seizures, optic nerve hypoplasia, growth retardation and hypotonia. Although CASK knockout mice were previously reported to exhibit perinatal lethality and a 3-fold increased apoptotic rate in the brain, CASK deletion was not found to affect neuronal physiology and their electrical properties. The pathogenesis of CASK associated disorders and the potential function of CASK therefore remains unknown. Here, using Cre-LoxP mediated gene excision experiments; we demonstrate that deleting CASK specifically from mouse cerebellar neurons does not alter the cerebellar architecture or function. We demonstrate that the neuron-specific deletion of CASK in mice does not cause perinatal lethality but induces severe recurrent epileptic seizures and growth retardation before the onset of adulthood. Furthermore, we demonstrate that although neuron-specific haploinsufficiency of CASK is inconsequential, the CASK mutation associated human phenotypes are replicated with high fidelity in CASK heterozygous knockout female mice (CASK(+/-)). These data suggest that CASK-related phenotypes are not purely neuronal in origin. Surprisingly, the observed microcephaly in CASK(+/-) animals is not associated with a specific loss of CASK null brain cells indicating that CASK regulates postnatal brain growth in a non-cell autonomous manner. Using biochemical assay, we also demonstrate that CASK can interact with metabolic proteins. CASK knockdown in human cell lines cause reduced cellular respiration and CASK(+/-) mice display abnormalities in muscle and brain oxidative metabolism, suggesting a novel function of CASK in metabolism. Our data implies that some phenotypic components of CASK heterozygous deletion mutation associated disorders represent systemic manifestation of metabolic stress and therefore amenable to therapeutic intervention.Electronic supplementary materialThe online version of this article (doi:10.1186/s40478-016-0295-6) contains supplementary material, which is available to authorized users.

Highlights

CASK is an evolutionarily conserved gene which encodes for a member of the membrane-associated guanylate kinase (MAGUK) protein family [31]
It has been demonstrated that mice carrying a floxed CASK gene (CASKfloxed) express ~ 33 % CASK compared to the wildtype littermates, and exhibit hypoplasia of cerebellar vermis [3, 45]
In contrast to CASK, only a minor fraction of PSD95 is present in the aqueous phase (Fig. 5d). These results suggest that a large fraction of CASK protein may be cytosolic in the mouse brain, and in this aspect CASK differs substantially from other MAGUK proteins such as PSD95, which is tethered to the membrane to orchestrate cell-to-cell signaling

Summary

Introduction

CASK is an evolutionarily conserved gene which encodes for a member of the membrane-associated guanylate kinase (MAGUK) protein family [31]. In mammals CASK was discovered due to its ability to bind to the cytosolic tail of neuronal adhesion molecules neurexins and is primarily identified as a scaffolding protein at the neuronal synapse [21]. CASK deletion does not alter synapse formation in C. elegans [25], Drosophila [56] or mouse [3]. CASK ortholog lin-2 was identified in C. elegans as early as 1980 and was found in screens for cell lineage specificity rather than synaptic function [16, 24]. CASK evolved before the emergence of the nervous system [31, 43] and is present in tissues from all three germ layers in mammals [21, 60]. CASK has been noted to play a role in wide variety of cellular functions including transcription regulation [27], insulin signaling and secretion [67, 72], and cancer biology [68]

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