Studies in Drosophila help implicate a variant in the human MTSS2/MTSS1L gene in a a syndromic form of intellectual disability

Am J Hum Genet. 2022 Oct 6;109(10):1923-1931. doi: 10.1016/j.ajhg.2022.08.011

The recurrent de novo c.2011C>T missense variant in MTSS2 causes syndromic intellectual disability

Huang Y, Lemire G, Briere LC, Liu F, Wessels MW, Wang X, Osmond M, Kanca O, Lu S, High FA, Walker MA, Rodan LH; Undiagnosed Diseases Network; Care4Rare Canada Consortium, Kernohan KD, Sweetser DA, Boycott KM, Bellen HJ

Abstract:

MTSS2, also known as MTSS1L, binds to plasma membranes and modulates their bending. MTSS2 is highly expressed in the central nervous system (CNS) and appears to be involved in activity-dependent synaptic plasticity. Variants in MTSS2 have not yet been associated with a human phenotype in OMIM. Here we report five individuals with the same heterozygous de novo variant in MTSS2 (GenBank: NM_138383.2: c.2011C>T [p.Arg671Trp]) identified by exome sequencing. The individuals present with global developmental delay, mild intellectual disability, ophthalmological anomalies, microcephaly or relative microcephaly, and shared mild facial dysmorphisms. Immunoblots of fibroblasts from two affected individuals revealed that the variant does not significantly alter MTSS2 levels. We modeled the variant in Drosophila and showed that the fly ortholog missing-in-metastasis (mim) was widely expressed in most neurons and a subset of glia of the CNS. Loss of mim led to a reduction in lifespan, impaired locomotor behavior, and reduced synaptic transmission in adult flies. Expression of the human MTSS2 reference cDNA rescued the mim loss-of-function (LoF) phenotypes, whereas the c.2011C>T variant had decreased rescue ability compared to the reference, suggesting it is a partial LoF allele. However, elevated  expression of the variant, but not the reference MTSS2 cDNA, led to similar defects as observed by mim LoF, suggesting that the variant is toxic and may act as a dominant-negative allele when expressed in flies. In summary, our findings support that mim is important for appropriate neural function, and that the MTSS2 c.2011C>T variant causes a syndromic form of intellectual disability.

DOI: 10.1016/j.ajhg.2022.08.011
PMID: 36067766

Video Protocol: Fly models of heart function

J Vis Exp. 2022 Aug 25;(186). doi: 10.3791/63939.

Developing Drosophila melanogaster Models for Imaging and Optogenetic Control of Cardiac Function

Gracheva E, Wang F, Matt A, Liang H, Fishman M, Zhou C

Abstract:

Using Drosophila melanogaster (fruit fly) as a model organism has ensured significant progress in many areas of biological science, from cellular organization and genomic investigations to behavioral studies. Due to the accumulated scientific knowledge, in recent years, Drosophila was brought to the field of modeling human diseases, including heart disorders. The presented work describes the experimental system for monitoring and manipulating the heart function in the context of a whole live organism using red light (617 nm) and without invasive procedures. Control over the heart was achieved using optogenetic tools. Optogenetics combines the expression of light-sensitive transgenic opsins and their optical activation to regulate the biological tissue of interest. In this work, a custom integrated optical coherence tomography (OCT) imaging and optogenetic stimulation system was used to visualize and modulate the functioning D. melanogaster heart at the 3rd instar larval and early pupal developmental stages. The UAS/GAL4 dual genetic system was employed to express halorhodopsin (eNpHR2.0) and red-shifted channelrhodopsin (ReaChR), specifically in the fly heart. Details on preparing D. melanogaster for live OCT imaging and optogenetic pacing are provided. A lab-developed integration software processed the imaging data to create visual presentations and quantitative characteristics of Drosophila heart function. The results demonstrate the feasibility of initiating cardiac arrest and bradycardia caused by eNpHR2.0 activation and performing heart pacing upon ReaChR activation.

DOI: 10.3791/63939
PMID: 36094265

Fly model helps illuminate mechanisms underlying contribution of GEMIN4 in an inherited neurodevelopmental disorder

Am J Med Genet A. 2022 Oct;188(10):2932-2940. doi: 10.1002/ajmg.a.62894 

Further delineation of GEMIN4 related neurodevelopmental disorder with microcephaly, cataract, and renal abnormalities syndrome

Altassan R, Qudair A, Alokaili R, Alhasan K, Faqeih EA, Alhashem A, Alowain M, Alsayed M, Rahbeeni Z, Albadi L, Alkuraya FS, Anderson EN, Rajan D, Pandey UB

Abstract:

Pathogenic variants in GEMIN4 have recently been linked to an inherited autosomal recessive neurodevelopmental disorder characterized with microcephaly, cataracts, and renal abnormalities (NEDMCR syndrome). This report provides a retrospective review of 16 patients from 11 unrelated Saudi consanguineous families with GEMIN4 mutations. The cohort comprises 11 new and unpublished clinical details from five previously described patients. Only two missense, homozygous, pathogenic variants were found in all affected patients, suggesting a founder effect. All patients shared global developmental delay with variable ophthalmological, renal, and skeletal manifestations. In addition, we knocked down endogenous Drosophila GEMIN4 in neurons to further investigate the mechanism of the functional defects in affected patients. Our fly model findings demonstrated developmental defects and motor dysfunction suggesting that loss of GEMIN4 function is detrimental in vivo; likely similar to human patients. To date, this study presents the largest cohort of patients affected with GEMIN4 mutations. Considering that identifying GEMIN4 defects in patients presenting with neurodevelopmental delay and congenital cataract will help in early diagnosis, appropriate management and prevention plans that can be made for affected families.

DOI: 10.1002/ajmg.a.62894
PMID: 35861185

Drosophila studies contribute to a study associating variants of PP2A/PPP2R4 with juvenile-onset parkinsonism

Brain. 2022 Sep 8:awac326. doi: 10.1093/brain/awac326 

PTPA variants and impaired PP2A activity in early-onset parkinsonism with
intellectual disability

Fevga C, Tesson C, Mascaro AC, Courtin T, van Coller R, Sakka S, Ferraro F, Farhat N, Bardien S, Damak M, Carr J, Ferrien M, Boumeester V, Hundscheid J, Grillenzoni N, Kessissoglou IA, Kuipers DJS, Quadri M; French and Mediterranean Parkinson disease Genetics Study Group; International Parkinsonism Genetics Network, Corvol JC, Mhiri C, Hassan BA, Breedveld GJ, Lesage S, Mandemakers W, Brice A, Bonifati V

Abstract:

The protein phosphatase 2A complex (PP2A), the major Ser/Thr phosphatase in the brain, is involved in a number of signaling pathways and functions, including the regulation of crucial proteins for neurodegeneration, such as alpha-synuclein, tau, and LRRK2. Here, we report the identification of variants in the PTPA/PPP2R4 gene, encoding a major PP2A activator, in two families with early-onset parkinsonism and intellectual disability. We carried out clinical studies and genetic analyses, including genome-wide linkage analysis, whole-exome sequencing, and Sanger sequencing of candidate variants. We next performed functional studies on the disease-associated variants in cultured cells and knock-down of ptpa in Drosophila melanogaster. We first identified a homozygous PTPA variant, c.893T > G (p.Met298Arg), in patients from a South African family with early-onset parkinsonism and intellectual disability. Screening of a large series of additional families yielded a second homozygous variant, c.512C > A (p.Ala171Asp), in a Libyan family with a similar phenotype. Both variants co-segregate with disease in the respective families. The affected subjects display juvenile-onset parkinsonism and intellectual disability. The motor symptoms were responsive to treatment with levodopa and deep brain stimulation of the subthalamic nucleus. In overexpression studies, both the PTPA p.Ala171Asp and p.Met298Arg variants were associated with decreased PTPA RNA stability and decreased PTPA protein levels; the p.Ala171Asp variant additionally displayed decreased PTPA protein stability. Crucially, expression of both variants was associated with decreased PP2A complex levels and impaired PP2A phosphatase activation. PTPA ortholog knock-down in Drosophila neurons induced a significant impairment of locomotion in the climbing test. This defect was age-dependent and fully reversed by L-DOPA treatment. We conclude that bi-allelic missense PTPA variants associated with impaired activation of the PP2A phosphatase cause autosomal recessive early-onset parkinsonism with intellectual disability. Our findings might also provide new insights for understanding the role of the PP2A complex in the pathogenesis of more common forms of neurodegeneration.

DOI: 10.1093/brain/awac326
PMID: 36073231

Drosophila studies contribute to identification of a novel disease-associated gene, ZMYND8

Genet Med. 2022 Sep;24(9):1952-1966. doi: 10.1016/j.gim.2022.06.001

De Novo ZMYND8 variants result in an autosomal dominant neurodevelopmental
disorder with cardiac malformations

Dias KR, Carlston CM, Blok LER, De Hayr L, Nawaz U, Evans CA, Bayrak-Toydemir P, Htun S, Zhu Y, Ma A, Lynch SA, Moorwood C, Stals K, Ellard S, Bainbridge MN, Friedman J, Pappas JG, Rabin R, Nowak CB, Douglas J, Wilson TE, Guillen Sacoto MJ, Mullegama SV, Palculict TB, Kirk EP, Pinner JR, Edwards M, Montanari F, Graziano C, Pippucci T, Dingmann B, Glass I, Mefford HC, Shimoji T, Suzuki T, Yamakawa K, Streff H, Schaaf CP, Slavotinek AM, Voineagu I, Carey JC, Buckley MF, Schenck A, Harvey RJ, Roscioli T

Abstract:

PURPOSE: ZMYND8 encodes a multidomain protein that serves as a central interactive hub for coordinating critical roles in transcription regulation, chromatin remodeling, regulation of super-enhancers, DNA damage response and tumor suppression. We delineate a novel neurocognitive disorder caused by variants in the ZMYND8 gene. 

METHODS: An international collaboration, exome sequencing, molecular modeling, yeast two-hybrid assays, analysis of available transcriptomic data and a knockdown Drosophila model were used to characterize the ZMYND8 variants. 

RESULTS: ZMYND8 variants were identified in 11 unrelated individuals; 10 occurred de novo and one suspected de novo; 2 were truncating, 9 were missense, of which one was recurrent. The disorder is characterized by intellectual disability with variable cardiovascular, ophthalmologic and minor skeletal anomalies. Missense variants in the PWWP domain of ZMYND8 abolish the interaction with Drebrin and missense variants in the MYND domain disrupt the interaction with GATAD2A. ZMYND8 is broadly expressed across cell types in all brain regions and shows highest expression in the early stages of brain development. Neuronal knockdown of the Drosophila ZMYND8 ortholog results in decreased habituation learning, consistent with a role in cognitive function. 

CONCLUSION: We present genomic and functional evidence for disruption of ZMYND8 as a novel etiology of syndromic intellectual disability.

DOI: 10.1016/j.gim.2022.06.001
PMID: 35916866

Assay in fly eye contributes to study related to ALS & FTD

J Biol Chem. 2022 Aug;298(8):102191. doi: 10.1016/j.jbc.2022.102191. 

Casein kinase 1δ/ε phosphorylates fused in sarcoma (FUS) and ameliorates FUS-mediated neurodegeneration

Kishino Y, Matsukawa K, Matsumoto T, Miyazaki R, Wakabayashi T, Nonaka T, Kametani F, Hasegawa M, Hashimoto T, Iwatsubo T

From the abstract:

Aberrant cytoplasmic accumulation of an RNA-binding protein, fused in sarcoma (FUS), characterizes the neuropathology of subtypes of ALS and frontotemporal lobar degeneration ... we show that casein kinase 1δ (CK1δ) phosphorylates FUS at 10 serine/threonine residues in vitro ... We also show that phosphorylation by CK1δ or CK1ε significantly increased the solubility of FUS in human embryonic kidney 293 cells. In transgenic Drosophila that overexpress wt or P525L ALS-mutant human FUS in the retina or in neurons, we found coexpression of human CK1δ or its Drosophila isologue Dco in the photoreceptor neurons significantly ameliorated the observed retinal degeneration, and neuronal coexpression of human CK1δ extended fly life span. .. our data suggest a novel regulatory mechanism of the assembly and toxicity of FUS through CK1δ/CK1ε-mediated phosphorylation, which could represent a potential therapeutic target in FUS proteinopathies.

DOI: 10.1016/j.jbc.2022.102191
PMCID: PMC9293781
PMID: 35753345

Multi-species study identifies the vacuolar H+ ATPase component ATP6V0C as a human disease-associated gene

Brain. 2022 Sep 8:awac330. doi: 10.1093/brain/awac330

ATP6V0C variants impair vacuolar V-ATPase causing a neurodevelopmental disorder
often associated with epilepsy

Mattison KA, Tossing G, Mulroe F, Simmons C, Butler KM, Schreiber A, Alsadah A, Neilson DE, Naess K, Wedell A, Wredenberg A, Sorlin A, McCann E, Burghel GJ, Menendez B, Hoganson GE, Botto LD, Filloux FM, Aledo-Serrano Á, Gil-Nagel A, Tatton-Brown K, Verbeek NE, van Hirtum-Das M, Breckpot J, Hammer TB, Møller RS, Whitney A, Douglas AGL, Kharbanda M, Brunetti-Pierri N, Morleo M, Nigro V, May HJ, Tao JX, Argili E, Sherr EH, Dobyns WB, Consortium GER, Baines RA, Warwicker J, Parker JA, Banka S, Campeau PM, Escayg A

Abstract:

The vacuolar H+-ATPase (V-ATPase) is an enzymatic complex that functions in an ATP-dependent manner to pump protons across membranes and acidify organelles, thereby creating the proton/pH gradient required for membrane trafficking by several different types of transporters. We describe heterozygous point variants in ATP6V0C, encoding the c-subunit in the membrane bound integral domain of the V-ATPase, in 27 patients with neurodevelopmental abnormalities with or without epilepsy. Corpus callosum hypoplasia and cardiac abnormalities were also present in some patients. In silico modeling suggested that the patient variants interfere with the interactions between the ATP6V0C and ATP6V0A subunits during ATP hydrolysis. Consistent with decreased V-ATPase activity, functional analyses conducted in Saccharomyces cerevisiae revealed reduced LysoSensor fluorescence and reduced growth in media containing varying concentrations of CaCl2. Knockdown of ATP6V0C in Drosophila resulted in increased duration of seizure-like behavior, and the expression of selected patient variants in Caenorhabditis elegans led to reduced growth, motor dysfunction, and reduced lifespan. In summary, this study establishes ATP6V0C as an important disease gene, describes the clinical features of the associated neurodevelopmental disorder, and provides insight into disease mechanisms.

DOI: 10.1093/brain/awac330
PMID: 36074901