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Patel PA, LaConte LEW, Liang C, Cecere T, Rajan D, Srivastava S, Mukherjee K. Genetic evidence for splicing-dependent structural and functional plasticity in CASK protein. J Med Genet 2024:jmg-2023-109747. [PMID: 38670634 DOI: 10.1136/jmg-2023-109747] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Accepted: 04/14/2024] [Indexed: 04/28/2024]
Abstract
BACKGROUND Pontocerebellar hypoplasia (PCH) may present with supratentorial phenotypes and is often accompanied by microcephaly. Damaging mutations in the X-linked gene CASK produce self-limiting microcephaly with PCH in females but are often lethal in males. CASK deficiency leads to early degeneration of cerebellar granule cells but its role in other regions of the brain remains uncertain. METHOD We generated a conditional Cask knockout mice and deleted Cask ubiquitously after birth at different times. We examined the clinical features in several subjects with damaging mutations clustered in the central part of the CASK protein. We have performed phylogenetic analysis and RT-PCR to assess the splicing pattern within the same protein region and performed in silico structural analysis to examine the effect of splicing on the CASK's structure. RESULT We demonstrate that deletion of murine Cask after adulthood does not affect survival but leads to cerebellar degeneration and ataxia over time. Intriguingly, damaging hemizygous CASK mutations in boys who display microcephaly and cerebral dysfunction but without PCH are known. These mutations are present in two vertebrate-specific CASK exons. These exons are subject to alternative splicing both in forebrain and hindbrain. Inclusion of these exons differentially affects the molecular structure and hence possibly the function/s of the CASK C-terminus. CONCLUSION Loss of CASK function disproportionately affects the cerebellum. Clinical data, however, suggest that CASK may have additional vertebrate-specific function/s that play a role in the mammalian forebrain. Thus, CASK has an ancient function shared between invertebrates and vertebrates as well as novel vertebrate-specific function/s.
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Affiliation(s)
- Paras A Patel
- Fralin Biomedical Research Institute at VTC, Roanoke, Virginia, USA
| | - Leslie E W LaConte
- Fralin Biomedical Research Institute at VTC, Roanoke, Virginia, USA
- Basic Science Education, Virginia Tech Carilion School of Medicine, Roanoke, VA, USA
| | - Chen Liang
- Fralin Biomedical Research Institute at VTC, Roanoke, Virginia, USA
| | - Thomas Cecere
- Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA
| | - Deepa Rajan
- University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA
| | - Sarika Srivastava
- Fralin Biomedical Research Institute at VTC, Roanoke, Virginia, USA
- Department of Genetics, The University of Alabama at Birmingham Heersink School of Medicine, Birmingham, Alabama, USA
| | - Konark Mukherjee
- Fralin Biomedical Research Institute at VTC, Roanoke, Virginia, USA
- Department of Genetics, The University of Alabama at Birmingham Heersink School of Medicine, Birmingham, Alabama, USA
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Aparicio JG, Hopp H, Harutyunyan N, Stewart C, Cobrinik D, Borchert M. Aberrant gene expression yet undiminished retinal ganglion cell genesis in iPSC-derived models of optic nerve hypoplasia. Ophthalmic Genet 2024; 45:1-15. [PMID: 37807874 PMCID: PMC10841193 DOI: 10.1080/13816810.2023.2253902] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2023] [Accepted: 08/26/2023] [Indexed: 10/10/2023]
Abstract
BACKGROUND Optic nerve hypoplasia (ONH), the leading congenital cause of permanent blindness, is characterized by a retinal ganglion cell (RGC) deficit at birth. Multifactorial developmental events are hypothesized to underlie ONH and its frequently associated neurologic and endocrine abnormalities; however, environmental influences are unclear and genetic underpinnings are unexplored. This work investigates the genetic contribution to ONH RGC production and gene expression using patient induced pluripotent stem cell (iPSC)-derived retinal organoids (ROs). MATERIALS AND METHODS iPSCs produced from ONH patients and controls were differentiated to ROs. RGC genesis was assessed using immunofluorescence and flow cytometry. Flow-sorted BRN3+ cells were collected for RNA extraction for RNA-Sequencing. Differential gene expression was assessed using DESeq2 and edgeR. PANTHER was employed to identify statistically over-represented ontologies among the differentially expressed genes (DEGs). DEGs of high interest to ONH were distinguished by assessing function, mutational constraint, and prior identification in ONH, autism and neurodevelopmental disorder (NDD) studies. RESULTS RGC genesis and survival were similar in ONH and control ROs. Differential expression of 70 genes was identified in both DESeq2 and edgeR analyses, representing a ~ 4-fold higher percentage of DEGs than in randomized study participants. DEGs showed trends towards over-representation of validated NDD genes and ONH exome variant genes. Among the DEGs, RAPGEF4 and DMD had the greatest number of disease-relevant features. CONCLUSIONS ONH genetic background was not associated with impaired RGC genesis but was associated with DEGs exhibiting disease contribution potential. This constitutes some of the first evidence of a genetic contribution to ONH.
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Affiliation(s)
- Jennifer G. Aparicio
- The Vision Center and The Saban Research Institute,
Children’s Hospital Los Angeles, Los Angeles, CA, USA
| | - Hanno Hopp
- The Vision Center and The Saban Research Institute,
Children’s Hospital Los Angeles, Los Angeles, CA, USA
| | - Narine Harutyunyan
- The Vision Center and The Saban Research Institute,
Children’s Hospital Los Angeles, Los Angeles, CA, USA
| | - Carly Stewart
- The Vision Center and The Saban Research Institute,
Children’s Hospital Los Angeles, Los Angeles, CA, USA
| | - David Cobrinik
- The Vision Center and The Saban Research Institute,
Children’s Hospital Los Angeles, Los Angeles, CA, USA
- Department of Biochemistry & Molecular Medicine, Keck
School of Medicine, University of Southern California, Los Angeles, CA, USA
- Norris Comprehensive Cancer Center, Keck School of
Medicine, University of Southern California, Los Angeles, CA, USA
- USC Roski Eye Institute, Department of Ophthalmology, Keck
School of Medicine, University of Southern California, Los Angeles, CA, USA
| | - Mark Borchert
- The Vision Center and The Saban Research Institute,
Children’s Hospital Los Angeles, Los Angeles, CA, USA
- USC Roski Eye Institute, Department of Ophthalmology, Keck
School of Medicine, University of Southern California, Los Angeles, CA, USA
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3
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Tello JA, Jiang L, Zohar Y, Restifo LL. Drosophila CASK regulates brain size and neuronal morphogenesis, providing a genetic model of postnatal microcephaly suitable for drug discovery. Neural Dev 2023; 18:6. [PMID: 37805506 PMCID: PMC10559581 DOI: 10.1186/s13064-023-00174-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2023] [Accepted: 09/08/2023] [Indexed: 10/09/2023] Open
Abstract
BACKGROUND CASK-related neurodevelopmental disorders are untreatable. Affected children show variable severity, with microcephaly, intellectual disability (ID), and short stature as common features. X-linked human CASK shows dosage sensitivity with haploinsufficiency in females. CASK protein has multiple domains, binding partners, and proposed functions at synapses and in the nucleus. Human and Drosophila CASK show high amino-acid-sequence similarity in all functional domains. Flies homozygous for a hypomorphic CASK mutation (∆18) have motor and cognitive deficits. A Drosophila genetic model of CASK-related disorders could have great scientific and translational value. METHODS We assessed the effects of CASK loss of function on morphological phenotypes in Drosophila using established genetic, histological, and primary neuronal culture approaches. NeuronMetrics software was used to quantify neurite-arbor morphology. Standard nonparametric statistics methods were supplemented by linear mixed effects modeling in some cases. Microfluidic devices of varied dimensions were fabricated and numerous fluid-flow parameters were used to induce oscillatory stress fields on CNS tissue. Dissociation into viable neurons and neurite outgrowth in vitro were assessed. RESULTS We demonstrated that ∆18 homozygous flies have small brains, small heads, and short bodies. When neurons from developing CASK-mutant CNS were cultured in vitro, they grew small neurite arbors with a distinctive, quantifiable "bushy" morphology that was significantly rescued by transgenic CASK+. As in humans, the bushy phenotype showed dosage-sensitive severity. To overcome the limitations of manual tissue trituration for neuronal culture, we optimized the design and operation of a microfluidic system for standardized, automated dissociation of CNS tissue into individual viable neurons. Neurons from CASK-mutant CNS dissociated in the microfluidic system recapitulate the bushy morphology. Moreover, for any given genotype, device-dissociated neurons grew larger arbors than did manually dissociated neurons. This automated dissociation method is also effective for rodent CNS. CONCLUSIONS These biological and engineering advances set the stage for drug discovery using the Drosophila model of CASK-related disorders. The bushy phenotype provides a cell-based assay for compound screening. Nearly a dozen genes encoding CASK-binding proteins or transcriptional targets also have brain-development mutant phenotypes, including ID. Hence, drugs that improve CASK phenotypes might also benefit children with disorders due to mutant CASK partners.
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Affiliation(s)
- Judith A Tello
- Graduate Interdisciplinary Program in Neuroscience, University of Arizona, Tucson, AZ, 85721, USA
- Department of Neurology, University of Arizona Health Sciences, 1501 N. Campbell Ave, Tucson, AZ, 85724-5023, USA
- Present address: Department of Molecular Pathobiology, College of Dentistry, New York University, New York, NY, 10010, USA
| | - Linan Jiang
- Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ, 85721, USA
| | - Yitshak Zohar
- Department of Aerospace and Mechanical Engineering, University of Arizona, Tucson, AZ, 85721, USA
- Department of Biomedical Engineering, University of Arizona, Tucson, AZ, 85721, USA
- BIO5 Interdisciplinary Research Institute, University of Arizona, Tucson, AZ, 85721, USA
| | - Linda L Restifo
- Graduate Interdisciplinary Program in Neuroscience, University of Arizona, Tucson, AZ, 85721, USA.
- Department of Neurology, University of Arizona Health Sciences, 1501 N. Campbell Ave, Tucson, AZ, 85724-5023, USA.
- BIO5 Interdisciplinary Research Institute, University of Arizona, Tucson, AZ, 85721, USA.
- Department of Cellular & Molecular Medicine, University of Arizona Health Sciences, Tucson, AZ, 85724, USA.
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The Non-Linear Path from Gene Dysfunction to Genetic Disease: Lessons from the MICPCH Mouse Model. Cells 2022; 11:cells11071131. [PMID: 35406695 PMCID: PMC8997851 DOI: 10.3390/cells11071131] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2022] [Revised: 03/09/2022] [Accepted: 03/24/2022] [Indexed: 11/17/2022] Open
Abstract
Most human disease manifests as a result of tissue pathology, due to an underlying disease process (pathogenesis), rather than the acute loss of specific molecular function(s). Successful therapeutic strategies thus may either target the correction of a specific molecular function or halt the disease process. For the vast majority of brain diseases, clear etiologic and pathogenic mechanisms are still elusive, impeding the discovery or design of effective disease-modifying drugs. The development of valid animal models and their proper characterization is thus critical for uncovering the molecular basis of the underlying pathobiological processes of brain disorders. MICPCH (microcephaly and pontocerebellar hypoplasia) is a monogenic condition that results from variants of an X-linked gene, CASK (calcium/calmodulin-dependent serine protein kinase). CASK variants are associated with a wide range of clinical presentations, from lethality and epileptic encephalopathies to intellectual disabilities, microcephaly, and autistic traits. We have examined CASK loss-of-function mutations in model organisms to simultaneously understand the pathogenesis of MICPCH and the molecular function/s of CASK. Our studies point to a highly complex relationship between the potential molecular function/s of CASK and the phenotypes observed in model organisms and humans. Here we discuss the implications of our observations from the pathogenesis of MICPCH as a cautionary narrative against oversimplifying molecular interpretations of data obtained from genetically modified animal models of human diseases.
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5
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Resveratrol protects retinal ganglion cell axons through regulation of the SIRT1-JNK pathway. Exp Eye Res 2020; 200:108249. [PMID: 32956685 DOI: 10.1016/j.exer.2020.108249] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 08/12/2020] [Accepted: 09/14/2020] [Indexed: 01/21/2023]
Abstract
It is reported that Ischemia and reperfusion damage (I/R damage) can lead to retinal ganglion cell (RGC) death and neurodegeneration, which in turn can lead to irreversible vision loss. In this study, we sought to understand the neuroprotective effect of resveratrol, the important activator of sirtuin1 (SIRT1), on RGC survival in I/R damage model and the molecular mechanism that mediate this effect. Our results show that resveratrol could reverse axonal swelling, holes, and the chaos of the nucleus in axons of RGCs caused by I/R. At the same time, resveratrol could also reverse the activation of retinal astrocytes and the loss of RGCs caused by I/R. Resveratrol increased the expression of SIRT1 while decreasing the phosphorylation of N-terminal kinase (JNK). SP600125(JNK inhibitor) decreased the phosphorylation of JNK while increasing the expression of SIRT1, indicating that SIRT1 and JNK can interact with each other. Simultaneous administration of resveratrol and sirtinol (SIRT1 inhibitor) neither increased the expression of SIRT1 nor decreased the phosphorylation of JNK, indicating that resveratrol affects the phosphorylation of JNK by SIRT1. In total, our research shows that resveratrol treatment significantly reduces apoptosis and axonal degeneration of RGCs, and this protection is partly mediated through the SIRT1-JNK pathway.
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Patel PA, Liang C, Arora A, Vijayan S, Ahuja S, Wagley PK, Settlage R, LaConte LEW, Goodkin HP, Lazar I, Srivastava S, Mukherjee K. Haploinsufficiency of X-linked intellectual disability gene CASK induces post-transcriptional changes in synaptic and cellular metabolic pathways. Exp Neurol 2020; 329:113319. [PMID: 32305418 DOI: 10.1016/j.expneurol.2020.113319] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2019] [Revised: 04/04/2020] [Accepted: 04/15/2020] [Indexed: 12/17/2022]
Abstract
Heterozygous mutations in the X-linked gene CASK are associated with intellectual disability, microcephaly, pontocerebellar hypoplasia, optic nerve hypoplasia and partially penetrant seizures in girls. The Cask+/- heterozygous knockout female mouse phenocopies the human disorder and exhibits postnatal microencephaly, cerebellar hypoplasia and optic nerve hypoplasia. It is not known if Cask+/- mice also display seizures, nor is known the molecular mechanism by which CASK haploinsufficiency produces the numerous documented phenotypes. 24-h video electroencephalography demonstrates that despite sporadic seizure activity, the overall electrographic patterns remain unaltered in Cask+/- mice. Additionally, seizure threshold to the commonly used kindling agent, pentylenetetrazol, remains unaltered in Cask+/- mice, indicating that even in mice the seizure phenotype is only partially penetrant and may have an indirect mechanism. RNA sequencing experiments on Cask+/- mouse brain uncovers a very limited number of changes, with most differences arising in the transcripts of extracellular matrix proteins and the transcripts of a group of nuclear proteins. In contrast to limited changes at the transcript level, quantitative whole-brain proteomics using iTRAQ quantitative mass-spectrometry reveals major changes in synaptic, metabolic/mitochondrial, cytoskeletal, and protein metabolic pathways. Unbiased protein-protein interaction mapping using affinity chromatography demonstrates that CASK may form complexes with proteins belonging to the same functional groups in which altered protein levels are observed. We discuss the mechanism of the observed changes in the context of known molecular function/s of CASK. Overall, our data indicate that the phenotypic spectrum of female Cask+/- mice includes sporadic seizures and thus closely parallels that of CASK haploinsufficient girls; the Cask+/- mouse is thus a face-validated model for CASK-related pathologies. We therefore surmise that CASK haploinsufficiency is likely to affect brain structure and function due to dysregulation of several cellular pathways including synaptic signaling and cellular metabolism.
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Affiliation(s)
- P A Patel
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, United States; Graduate Program in Translational Biology, Medicine, and Health, Virginia Tech, Blacksburg, VA, United States
| | - C Liang
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, United States
| | - A Arora
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, United States
| | - S Vijayan
- School of Neuroscience, Virginia Tech, Blacksburg, VA, United States
| | - S Ahuja
- Biological Sciences, Virginia Tech, Blacksburg, VA, United States
| | - P K Wagley
- Neurology, University of Virginia, Charlottesville, VA, USA
| | - R Settlage
- Advanced Research Computing, Virginia Tech, Blacksburg, VA, United States
| | - L E W LaConte
- Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, United States
| | - H P Goodkin
- Neurology, University of Virginia, Charlottesville, VA, USA
| | - I Lazar
- Biological Sciences, Virginia Tech, Blacksburg, VA, United States
| | - S Srivastava
- Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, United States
| | - K Mukherjee
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, United States; Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, VA, United States; Department of Psychiatry and Behavioral Medicine, Virginia Tech Carilion School of Medicine, Roanoke, VA, United States.
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7
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Kerr A, Patel PA, LaConte LEW, Liang C, Chen CK, Shah V, Fox MA, Mukherjee K. Non-Cell Autonomous Roles for CASK in Optic Nerve Hypoplasia. Invest Ophthalmol Vis Sci 2019; 60:3584-3594. [PMID: 31425583 PMCID: PMC6701874 DOI: 10.1167/iovs.19-27197] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Purpose Heterozygous mutations in the essential X-linked gene CASK associate with optic nerve hypoplasia (ONH) and other retinal disorders in girls. CASK+/− heterozygous knockout mice with mosaic CASK expression exhibit ONH with a loss of retinal ganglion cells (RGCs) but no changes in retinal morphology. It remains unclear if CASK deficiency selectively affects RGCs or also affects other retinal cells. Furthermore, it is not known if CASK expression in RGCs is critical for optic nerve (ON) development and maintenance. Methods The visual behavior of CASK+/− mice was assessed and electroretinography (ERG) was performed. Using a mouse line with a floxed CASK gene that expresses approximately 40% CASK globally in all cells (hypomorph) under hemizygous and homozygous conditions, we investigated effects of CASK reduction on the retina and ON. CASK then was completely deleted from RGCs to examine its cell-autonomous role. Finally, for the first time to our knowledge, we describe a hemizygous CASK missense mutation in a boy with ONH. Results CASK+/− heterozygous mutant mice display reduced visual contrast sensitivity, but ERG is indistinguishable from wildtype. CASK hypomorph mice exhibit ONH, but deletion of CASK from RGCs in this background does not exacerbate the condition. The boy with ONH harbors a missense mutation (p.Pro673Leu) that destabilizes CASK and weakens the crucial CASK–neurexin interaction. Conclusions Our results demonstrate that mosaic or global reduction in CASK expression and/or function disproportionately affects RGCs. CASK expression in RGCs does not appear critical for cell survival, indicating a noncell autonomous role for CASK in the development of ON.
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Affiliation(s)
- Alicia Kerr
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia, United States.,Graduate Program in Translational Biology, Medicine, and Health, Virginia Tech, Blacksburg, Virginia, United States
| | - Paras A Patel
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia, United States.,Graduate Program in Translational Biology, Medicine, and Health, Virginia Tech, Blacksburg, Virginia, United States
| | - Leslie E W LaConte
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia, United States.,Department of Basic Science Education, Virginia Tech Carilion School of Medicine, Roanoke, Virginia, United States
| | - Chen Liang
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia, United States
| | - Ching-Kang Chen
- Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, United States
| | - Veeral Shah
- Department of Ophthalmology, Baylor College of Medicine, Houston, Texas, United States.,Texas Children's Hospital, Houston, Texas, United States
| | - Michael A Fox
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia, United States.,Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States.,Department of Pediatrics, Virginia Tech Carilion School of Medicine, Roanoke, Virginia, United States
| | - Konark Mukherjee
- Center for Neurobiology Research, Fralin Biomedical Research Institute at Virginia Tech Carilion, Roanoke, Virginia, United States.,Department of Psychiatry and Behavioral Medicine, Virginia Tech Carilion School of Medicine, Roanoke, Virginia, United States
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8
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Studtmann C, LaConte LEW, Mukherjee K. Comments on: A de novo in-frame deletion of CASK gene causes early onset infantile spasms and supratentorial cerebral malformation in a female patient. Am J Med Genet A 2019; 179:2514-2516. [PMID: 31532018 DOI: 10.1002/ajmg.a.61358] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Revised: 08/02/2019] [Accepted: 08/27/2019] [Indexed: 11/06/2022]
Affiliation(s)
- Carleigh Studtmann
- Fralin Biomedical Research Institute, Roanoke, Virginia.,Graduate Program in Translational Biology, Medicine, and Health, Virginia Tech, Blacksburg, Virginia
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9
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LaConte LEW, Chavan V, DeLuca S, Rubin K, Malc J, Berry S, Gail Summers C, Mukherjee K. An N-terminal heterozygous missense CASK mutation is associated with microcephaly and bilateral retinal dystrophy plus optic nerve atrophy. Am J Med Genet A 2018; 179:94-103. [PMID: 30549415 DOI: 10.1002/ajmg.a.60687] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2018] [Revised: 09/26/2018] [Accepted: 10/17/2018] [Indexed: 11/08/2022]
Abstract
Heterozygous loss-of-function mutations in the X-linked gene CASK are associated with mental retardation and microcephaly with pontine and cerebellar hypoplasia (MICPCH) and ophthalmological disorders including optic nerve atrophy (ONA) and optic nerve hypoplasia (ONH). Recently, we have demonstrated that CASK(+/-) mice display ONH with 100% penetrance but exhibit no change in retinal lamination or structure. It is not clear if CASK loss-of-function predominantly affects retinal ganglion cells, or if other retinal cells like photoreceptors are also involved. Here, we report a heterozygous missense mutation in the N-terminal calcium/calmodulin-dependent kinase (CaMK) domain of the CASK protein in which a highly conserved leucine is mutated to the cyclic amino acid proline. In silico analysis suggests that the mutation may produce destabilizing structural changes. Experimentally, we observe pronounced misfolding and insolubility of the CASKL209P protein. Interestingly, the remaining soluble mutant protein fails to interact with Mint1, which specifically binds to CASK's CaMK domain, suggesting a mechanism for the phenotypes observed with the CASKL209P mutation. In addition to microcephaly, cerebellar hypoplasia and delayed development, the subject with the L209P mutation also presented with bilateral retinal dystrophy and ONA. Electroretinography indicated that rod photoreceptors are the most prominently affected cells. Our data suggest that the CASK interactions mediated by the CaMK domain may play a crucial role in retinal function, and thus, in addition to ONH, individuals with mutations in the CASK gene may exhibit other retinal disorders, depending on the nature of mutation.
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Affiliation(s)
| | - Vrushali Chavan
- Virginia Tech Carilion Research Institute, Roanoke, Virginia
| | | | - Karol Rubin
- Department of Genetics, Cell Biology & Development, University of Minnesota, Minneapolis, Minnesota
| | - Jessica Malc
- Virginia Tech Carilion Research Institute, Roanoke, Virginia
| | - Susan Berry
- Department of Pediatrics, University of Minnesota, Minneapolis, Minnesota.,Department of Genetics, Cell Biology & Development, University of Minnesota, Minneapolis, Minnesota
| | - C Gail Summers
- Department of Pediatrics, University of Minnesota, Minneapolis, Minnesota.,Department of Ophthalmology & Visual Neurosciences, University of Minnesota, Minneapolis, Minnesota
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10
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Two microcephaly-associated novel missense mutations in CASK specifically disrupt the CASK-neurexin interaction. Hum Genet 2018; 137:231-246. [PMID: 29426960 DOI: 10.1007/s00439-018-1874-3] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2017] [Accepted: 01/31/2018] [Indexed: 12/23/2022]
Abstract
Deletion and truncation mutations in the X-linked gene CASK are associated with severe intellectual disability (ID), microcephaly and pontine and cerebellar hypoplasia in girls (MICPCH). The molecular origin of CASK-linked MICPCH is presumed to be due to disruption of the CASK-Tbr-1 interaction. This hypothesis, however, has not been directly tested. Missense variants in CASK are typically asymptomatic in girls. We report three severely affected girls with heterozygous CASK missense mutations (M519T (2), G659D (1)) who exhibit ID, microcephaly, and hindbrain hypoplasia. The mutation M519T results in the replacement of an evolutionarily invariant methionine located in the PDZ signaling domain known to be critical for the CASK-neurexin interaction. CASKM519T is incapable of binding to neurexin, suggesting a critically important role for the CASK-neurexin interaction. The mutation G659D is in the SH3 (Src homology 3) domain of CASK, replacing a semi-conserved glycine with aspartate. We demonstrate that the CASKG659D mutation affects the CASK protein in two independent ways: (1) it increases the protein's propensity to aggregate; and (2) it disrupts the interface between CASK's PDZ (PSD95, Dlg, ZO-1) and SH3 domains, inhibiting the CASK-neurexin interaction despite residing outside of the domain deemed critical for neurexin interaction. Since heterozygosity of other aggregation-inducing mutations (e.g., CASKW919R) does not produce MICPCH, we suggest that the G659D mutation produces microcephaly by disrupting the CASK-neurexin interaction. Our results suggest that disruption of the CASK-neurexin interaction, not the CASK-Tbr-1 interaction, produces microcephaly and cerebellar hypoplasia. These findings underscore the importance of functional validation for variant classification.
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11
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Monavarfeshani A, Stanton G, Van Name J, Su K, Mills WA, Swilling K, Kerr A, Huebschman NA, Su J, Fox MA. LRRTM1 underlies synaptic convergence in visual thalamus. eLife 2018; 7:e33498. [PMID: 29424692 PMCID: PMC5826289 DOI: 10.7554/elife.33498] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2017] [Accepted: 02/08/2018] [Indexed: 11/13/2022] Open
Abstract
It has long been thought that the mammalian visual system is organized into parallel pathways, with incoming visual signals being parsed in the retina based on feature (e.g. color, contrast and motion) and then transmitted to the brain in unmixed, feature-specific channels. To faithfully convey feature-specific information from retina to cortex, thalamic relay cells must receive inputs from only a small number of functionally similar retinal ganglion cells. However, recent studies challenged this by revealing substantial levels of retinal convergence onto relay cells. Here, we sought to identify mechanisms responsible for the assembly of such convergence. Using an unbiased transcriptomics approach and targeted mutant mice, we discovered a critical role for the synaptic adhesion molecule Leucine Rich Repeat Transmembrane Neuronal 1 (LRRTM1) in the emergence of retinothalamic convergence. Importantly, LRRTM1 mutant mice display impairment in visual behaviors, suggesting a functional role of retinothalamic convergence in vision.
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Affiliation(s)
- Aboozar Monavarfeshani
- Developmental and Translational Neurobiology CenterVirginia Tech Carilion Research InstituteRoanokeUnited States
- Department of Biological SciencesVirginia TechBlacksburgUnited States
| | - Gail Stanton
- Developmental and Translational Neurobiology CenterVirginia Tech Carilion Research InstituteRoanokeUnited States
- Virginia Tech Carilion School of MedicineRoanokeUnited States
| | - Jonathan Van Name
- Developmental and Translational Neurobiology CenterVirginia Tech Carilion Research InstituteRoanokeUnited States
| | - Kaiwen Su
- Developmental and Translational Neurobiology CenterVirginia Tech Carilion Research InstituteRoanokeUnited States
| | - William A Mills
- Developmental and Translational Neurobiology CenterVirginia Tech Carilion Research InstituteRoanokeUnited States
- Translational Biology, Medicine, and Health Graduate ProgramVirginia TechBlacksburgUnited States
| | - Kenya Swilling
- Developmental and Translational Neurobiology CenterVirginia Tech Carilion Research InstituteRoanokeUnited States
| | - Alicia Kerr
- Developmental and Translational Neurobiology CenterVirginia Tech Carilion Research InstituteRoanokeUnited States
- Translational Biology, Medicine, and Health Graduate ProgramVirginia TechBlacksburgUnited States
| | | | - Jianmin Su
- Developmental and Translational Neurobiology CenterVirginia Tech Carilion Research InstituteRoanokeUnited States
| | - Michael A Fox
- Developmental and Translational Neurobiology CenterVirginia Tech Carilion Research InstituteRoanokeUnited States
- Department of Biological SciencesVirginia TechBlacksburgUnited States
- Virginia Tech Carilion School of MedicineRoanokeUnited States
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