development-knock-out-muscle-cell-lines-using-lentivirus-mediated

Development of Knock-Out Muscle Cell Lines using Lentivirus-Mediated CRISPR/Cas9 Gene Editing

One important application of clustered regulatory interspaced short palindromic repeats (CRISPR)/Cas 9 is the development of knock-out cell lines, ...

University Grenoble Alpes, INSERM, U1216, CHU Grenoble Alpes, Grenoble Institut Neurosciences

Fingerprint bodies are observed in a variety of clinical situations with no definite genetic cause identified so far. We report for the first time the association of fingerprint bodies with rods in a patient who developed a slowly progressive myopathy affecting the face and limb extremities. Ultrastructural examination first disclosed fingerprint bodies and on a second biopsy, associated cytoplasmic bodies and rods. Next Generation Sequencing panel of congenital nemaline myopathy genes allowed the identification of two novel variants, a deleterious missense variant (c.1628G>T, p.Arg543Leu) located in the WASP-homology 2 domain, and a deletion (c.366delG, p.Lys122AsnFs*6) in the LMOD3 gene, generally causing severe nemaline myopathy with antenatal onset and early death. Recently, a less severe phenotype similar to our case has been reported. Our study confirms the existence of milder phenotypes linked to LMOD3 mutations and underlines that fingerprint bodies, though not specific, may be an early ultrastructural marker that could be linked, among others, to nemaline myopathy.

Association of fingerprint bodies with rods in a case with mutations in the LMOD3 gene.

Lowe syndrome (LS) is an oculocerebrorenal syndrome of Lowe (OCRL1) genetic disorder resulting in a defect of the OCRL protein, a phosphatidylinositol-4,5-bisphosphate 5-phosphatase containing various domains including a Rho GTPase-activating protein (RhoGAP) homology domain catalytically inactive. We previously reported surgery-associated bleeding in patients with LS, suggestive of platelet dysfunction, accompanied with a mild thrombocytopenia in several patients. To decipher the role of OCRL in platelet functions and in megakaryocyte (MK) maturation, we conducted a case-control study on 15 patients with LS (NCT01314560). While all had a drastically reduced expression of OCRL, this deficiency did not affect platelet aggregability, but resulted in delayed thrombus formation on collagen under flow conditions, defective platelet spreading on fibrinogen and impaired clot retraction. We evidenced alterations of the myosin light chain phosphorylation (P-MLC), with defective Rac1 activity and, inversely, elevated active RhoA. Altered cytoskeleton dynamics was also observed in cultured patient MKs showing deficient proplatelet extension with increased P-MLC that was confirmed using control MKs transfected with OCRL-specific small interfering(si)RNA (siOCRL). Patients with LS also had an increased proportion of circulating barbell-shaped proplatelets. Our present study establishes that a deficiency of the OCRL protein results in a defective actomyosin cytoskeleton reorganisation in both MKs and platelets, altering both thrombopoiesis and some platelet responses to activation necessary to ensure haemostasis.

Role of oculocerebrorenal syndrome of Lowe (OCRL) protein in megakaryocyte maturation, platelet production and functions: a study in patients with Lowe syndrome.

The ryanodine receptor RyR1 is the main sarcoplasmic reticulum Ca channel in skeletal muscle and acts as a connecting link between electrical stimulation and Ca-dependent muscle contraction. Abnormal RyR1 activity compromises normal muscle function and results in various human disorders including malignant hyperthermia, central core disease, and centronuclear myopathy. However, RYR1 is one of the largest genes of the human genome and accumulates numerous missense variants of uncertain significance (VUS), precluding an efficient molecular diagnosis for many patients and families. Here we describe a recurrent RYR1 mutation previously classified as VUS, and we provide clinical, histological, and genetic data supporting its pathogenicity. The heterozygous c.12083C>T (p.Ser4028Leu) mutation was found in thirteen patients from nine unrelated congenital myopathy families with consistent clinical presentation, and either segregated with the disease in the dominant families or occurred de novo. The affected individuals essentially manifested neonatal or infancy-onset hypotonia, delayed motor milestones, and a benign disease course differing from classical RYR1-related muscle disorders. Muscle biopsies showed unspecific histological and ultrastructural findings, while RYR1-typical cores and internal nuclei were seen only in single patients. In conclusion, our data evidence the causality of the RYR1 c.12083C>T (p.Ser4028Leu) mutation in the development of an atypical congenital myopathy with gradually improving motor function over the first decades of life, and may direct molecular diagnosis for patients with comparable clinical presentation and unspecific histopathological features on the muscle biopsy.

John Rendu

University Grenoble Alpes, INSERM, U1216, CHU Grenoble Alpes, Grenoble Institut Neurosciences

Development of Knock-Out Muscle Cell Lines using Lentivirus-Mediated CRISPR/Cas9 Gene Editing