Improving CRISPR/Cas9 mutagenesis efficiency by delaying the early development of zebrafish embryos

CRISPR/Cas9 driven mutagenesis in zygotes is a popular tool for introducing targeted mutations in model organisms. Compared to mouse, mutagenesis in zebrafish is relatively inefficient and results in somatic mosaicism most likely due to a short single-cell stage of about 40 min. Here we explored two options to improve CRISPR/Cas9 mutagenesis in zebrafish—extending the single-cell stage and defining conditions for carrying out mutagenesis in oocytes prior to in vitro fertilization. Previous work has shown that ovarian fluid from North American salmon species (coho and chinook salmon) prolong oocyte survival ex vivo so that they are viable for hours instead of dying within minutes if left untreated. We found that commonly farmed rainbow trout (Oncorhynchus mykiss) ovarian fluid (RTOF) has similar effect on zebrafish oocyte viability. In order to prolong single-cell stage, we incubated zebrafish zygotes in hydrogen sulfide (H₂S) and RTOF but failed to see any effect. However, the reduction of temperature from standard 28 to 12 °C postponed the first cell division by about an hour. In addition, the reduction in temperature was associated with increased CRISPR/Cas9 mutagenesis rate. These results suggest that the easily applicable reduction in temperature facilitates CRISPR/Cas9 mutagenesis in zebrafish.

Optimizing the Handling of Invasive Fungal Sinusitis Surgical Specimens

Introduction/Objective

Invasive fungal sinusitis (IFS) is an aggressive disease characterized by invasion of fungal hyphae into tissue/neurovascular bundles. This project assessed the handling of IFS specimens and implemented protocols to improve turnaround time (TAT).

Methods

A retrospective review of cases accessioned with a clinical concern for IFS from 2014-2019 was performed. TAT for each step in the specimen processing was recorded. A flowchart was created using stakeholder interviews and a revised protocol was developed after assessing critical needs. Assessment of interventions was performed following implementation of the new protocol. The protocol will be evaluated by prospective direct case-by-case feedback and after a 6-month interval (projected August/2020). At 6-months, goals are a 24 hours median time between frozen section and sign-out and elimination of outliers (greater than 2 working days).

Results

We identified 53 specimens from 32 patients in the pre-intervention period (36 cases positive for IFS). Median time from frozen section to final sign-out was 28 (5-312) hours. Four areas for improvements were identified:

(1) triaging specimens to different protocols according to arrival time, (2) optimized triaging for available histology processors, (3) standardized GMS ordering, and (4) standardized case delivery/communication with sign-out staff. Interventions include: protocol for processing specimens based on time of day, new histology protocols to expedite GMS performance, an email group for rapid communication with staff pathologists and histology, and a worksheet/checklist to track each case. After implementation of the protocol, 8 cases from 7 patients were received. Median time from frozen section to final sign-out was reduced to 20 (2 – 50) hours.

Conclusion

The protocol for handling IFS specimens became live on 2/1/2020. It has reduced TAT of suspected IFS cases, from a median of 28 hours to 20 hours. The longest interval to sign-out went from312 hours to 50 hours.

Loss of mtDNA activates astrocytes and leads to spongiotic encephalopathy

Mitochondrial dysfunction manifests as different neurological diseases, but the mechanisms underlying the clinical variability remain poorly understood. To clarify whether different brain cells have differential sensitivity to mitochondrial dysfunction, we induced mitochondrial DNA (mtDNA) depletion in either neurons or astrocytes of mice, by inactivating Twinkle (TwKO), the replicative mtDNA helicase. Here we show that astrocytes, the most abundant cerebral cell type, are chronically activated upon mtDNA loss, leading to early-onset spongiotic degeneration of brain parenchyma, microgliosis and secondary neurodegeneration. Neuronal mtDNA loss does not, however, cause symptoms until 8 months of age. Findings in astrocyte-TwKO mimic neuropathology of Alpers syndrome, infantile-onset mitochondrial spongiotic encephalopathy caused by mtDNA maintenance defects. Our evidence indicates that (1) astrocytes are dependent on mtDNA integrity; (2) mitochondrial metabolism contributes to their activation; (3) chronic astrocyte activation has devastating consequences, underlying spongiotic encephalopathy; and that (4) astrocytes are a potential target for interventions.

Astrocytes in the brain are metabolically dynamic. Here, Ignatenko, Chilov and colleagues delete mitochondrial DNA (mtDNA) in a cell type specific manner, and show that inactivation of mtDNA helicase Twinkle in astrocytes leads to spongiotic encephalopathy.

Molecular analysis of Turkish mucopolysaccharidosis IVA (Morquio A) patients: identification of novel mutations in the N-acetylgalactosamine-6-sulfate sulfatase (GALNS) gene

Mucopolysaccharidosis IVA (MPS IVA) is a lysosomal storage disorder caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS; EC 3.1.6.4). The deficiency of N-acetylgalactosamine-6-sulfate sulfatase leads to lysosomal accumulation of undegraded glycosaminoglycans, keratan sulfate and chondroitin-6-sulfate. Mutation screening of the GALNS gene was performed by SSCP and direct sequence analyses using genomic DNA samples from 10 Morquio A patients. By nonradioactive SSCP screening, 6 different gene mutations and 2 polymorphisms were identified in 10 severely affected MPS IVA patients. Five of the mutations and one of the polymorphisms are novel. The vast majority of the gene alterations were found to be single nucleotide deletions (389delG, 929delG, and 763delT) or insertions (1232-1233insT). The other two mutations were one previously identified missense mutation (Q473X) and one novel nonsense (P179S) mutation. Together they account for 95% of the disease alleles of the patients investigated. Beside mutations, one previously identified E477 polymorphism and one novel W520 polymorphism were found among Turkish MPS IVA patients.

The molecular basis of glycogen storage disease type 1a: structure and function analysis of mutations in glucose-6-phosphatase

Glycogen storage disease type 1a is caused by a deficiency in glucose-6-phosphatase (G6Pase), a nine-helical endoplasmic reticulum transmembrane protein required for maintenance of glucose homeostasis. To date, 75 G6Pase mutations have been identified, including 48 mutations resulting in single-amino acid substitutions. However, only 19 missense mutations have been functionally characterized. Here, we report the results of structure and function studies of the 48 missense mutations and the DeltaF327 codon deletion mutation, grouped as active site, helical, and nonhelical mutations. The 5 active site mutations and 22 of the 31 helical mutations completely abolished G6Pase activity, but only 5 of the 13 nonhelical mutants were devoid of activity. Whereas the active site and nonhelical mutants supported the synthesis of G6Pase protein in a manner similar to that of the wild-type enzyme, immunoblot analysis showed that the majority (64.5%) of helical mutations destabilized G6Pase. Furthermore, we show that degradation of both wild-type and mutant G6Pase is inhibited by lactacystin, a potent proteasome inhibitor. Taken together, we have generated a data base of residual G6Pase activity retained by G6Pase mutants, established the critical roles of transmembrane helices in the stability and activity of this phosphatase, and shown that G6Pase is a substrate for proteasome-mediated degradation.

Sanfilippo syndrome in Turkey: Identification of novel mutations in subtypes A and B

Sanfilippo syndrome (mucopolysaccharidosis type III, MPS III) is a progressive disorder in which patients are characterized by severe central nervous system degeneration together with mild somatic disease. MPS III results from a deficiency in one of the four enzymes involved in the degradation of heparan sulfate, with sulfamidase (SGSH) being deficient in MPS IIIA and a-N-acetylglucosaminidase (NAGLU) deficient in MPS IIIB. Mutation screening using SSCP/heteroduplex analysis on genomic DNA fragments was performed in five Turkish MPS IIIA and eight Turkish MPS IIIB patients. In this study two mutations of SGSH were identified in MPS IIIA patients: R74C and the novel mutation P288S, and one polymorphism (IVS1+23 C>G). Five different mutations of NAGLU were identified in MPS IIIB patients: L682R, H248R, E153K, g.17703 A>G (novel), and T437I (novel). The clinical data of all patients are reported in detail. A high degree of genetic heterogeneity was observed in the Turkish MPS IIIA and MPS IIIB patients.