An Epilepsy-Associated CILK1 Variant Compromises KATNIP Regulation and Impairs Primary Cilia and Hedgehog Signaling

Area of Science:

• Cell Biology
• Genetics
• Neuroscience

Background:

• Mutations in human ciliogenesis associated kinase 1 (CILK1) are implicated in ciliopathies and epilepsy.
• While kinase domain mutations impair primary cilia function, the impact of mutations outside this domain is less understood.
• The A615T variant in CILK1, found in juvenile myoclonic epilepsy (JME), resides in the intrinsically disordered C-terminal region.

Purpose of the Study:

• To investigate the functional consequences of the CILK1 A615T variant, identified in JME, on primary cilia and associated signaling pathways.
• To determine the effect of heterozygous and homozygous expression of the CILK1 A612T mutant allele in mouse embryo fibroblasts (MEFs).

Main Methods:

• Generation of a knock-in mouse model mimicking the human CILK1 A615T variant.
• Analysis of ciliation rates, individual cilia length, and ciliary Hedgehog signaling in MEFs from wild-type and mutant mice.
• Gene expression profiling of wild-type versus mutant MEFs to identify changes in cilia-related molecular functions.
• Assessment of CILK1 A615T mutant protein levels in the presence of scaffold protein KATNIP.

Main Results:

• MEFs with heterozygous or homozygous A612T mutant alleles showed increased ciliation rates and shorter cilia.
• Upregulation of ciliary Hedgehog signaling was observed in mutant MEFs, indicating impaired primary cilia function.
• Gene expression analysis revealed significant alterations in cilia-related molecular functions and biological processes in mutant cells.
• KATNIP regulation of the CILK1 A615T mutant protein was compromised, affecting its expression levels.

Conclusions:

• A single A612T mutant allele of CILK1 is sufficient to impair primary cilia maintenance and ciliary Hedgehog signaling.
• The study highlights compromised KATNIP regulation of a JME-associated CILK1 variant, leading to cilia dysfunction.
• These findings provide mechanistic insights into how CILK1 variants contribute to ciliopathies and epilepsy.