Universal Code Equivalent of a Yeast Mitochondrial lntron Reading Frame Is Expressed into E. coli as a Specific Double Strand Endonuclease

International audienceThe intron of the mitochondrial21S rRNA gene of Sac-charomyces cerevisiae (rl intron) possesses a 235 codon long internal open reading frame (rl ORF) whose translation product determines the duplicative transposition of that intron during crosses between intron-plus strains (omega+) and intron-minus ones (omega-). Using site-directed mutagenesis, we have constructed a universal code equivalent of the rl ORF that, under appropriate promoter control, allows the overexpression in E. coli of a protein identical to the mitochondrial intron encoded "transposase". This protein exhibits a double strand endonuclease activity specific for the omega-site. This finding demonstrates , for the first time, the enzymatic activity of an intron encoded protein whose function is to promote the spreading of that intron by generating double strand breaks at a specific sequence within a gene

A novel microdeletion syndrome at 3q13.31 characterised by developmental delay, postnatal overgrowth, hypoplastic male genitals, and characteristic facial features

Item does not contain fulltextBACKGROUND: Congenital deletions affecting 3q11q23 have rarely been reported and only five cases have been molecularly characterised. Genotype-phenotype correlation has been hampered by the variable sizes and breakpoints of the deletions. In this study, 14 novel patients with deletions in 3q11q23 were investigated and compared with 13 previously reported patients. METHODS: Clinical data were collected from 14 novel patients that had been investigated by high resolution microarray techniques. Molecular investigation and updated clinical information of one cytogenetically previously reported patient were also included. RESULTS: The molecular investigation identified deletions in the region 3q12.3q21.3 with different boundaries and variable sizes. The smallest studied deletion was 580 kb, located in 3q13.31. Genotype-phenotype comparison in 24 patients sharing this shortest region of overlapping deletion revealed several common major characteristics including significant developmental delay, muscular hypotonia, a high arched palate, and recognisable facial features including a short philtrum and protruding lips. Abnormal genitalia were found in the majority of males, several having micropenis. Finally, a postnatal growth pattern above the mean was apparent. The 580 kb deleted region includes five RefSeq genes and two of them are strong candidate genes for the developmental delay: DRD3 and ZBTB20. CONCLUSION: A newly recognised 3q13.31 microdeletion syndrome is delineated which is of diagnostic and prognostic value. Furthermore, two genes are suggested to be responsible for the main phenotype.1 februari 201

MINPP1 prevents intracellular accumulation of the chelator inositol hexakisphosphate and is mutated in Pontocerebellar Hypoplasia

Inositol polyphosphates are vital metabolic and secondary messengers, involved in diverse cellular functions. Therefore, tight regulation of inositol polyphosphate metabolism is essential for proper cell physiology. Here, we describe an early-onset neurodegenerative syndrome caused by loss-of-function mutations in the multiple inositol-polyphosphate phosphatase 1 gene (MINPP1). Patients are found to have a distinct type of Pontocerebellar Hypoplasia with typical basal ganglia involvement on neuroimaging. We find that patient-derived and genome edited MINPP1−/− induced stem cells exhibit an inefficient neuronal differentiation combined with an increased cell death. MINPP1 deficiency results in an intracellular imbalance of the inositol polyphosphate metabolism. This metabolic defect is characterized by an accumulation of highly phosphorylated inositols, mostly inositol hexakisphosphate (IP6), detected in HEK293 cells, fibroblasts, iPSCs and differentiating neurons lacking MINPP1. In mutant cells, higher IP6 level is expected to be associated with an increased chelation of intracellular cations, such as iron or calcium, resulting in decreased levels of available ions. These data suggest the involvement of IP6-mediated chelation on Pontocerebellar Hypoplasia disease pathology and thereby highlight the critical role of MINPP1 in the regulation of human brain development and homeostasis

Seamless Gene Tagging by Endonuclease-Driven Homologous Recombination

Gene tagging facilitates systematic genomic and proteomic analyses but chromosomal tagging typically disrupts gene regulatory sequences. Here we describe a seamless gene tagging approach that preserves endogenous gene regulation and is potentially applicable in any species with efficient DNA double-strand break repair by homologous recombination. We implement seamless tagging in Saccharomyces cerevisiae and demonstrate its application for protein tagging while preserving simultaneously upstream and downstream gene regulatory elements. Seamless tagging is compatible with high-throughput strain construction using synthetic genetic arrays (SGA), enables functional analysis of transcription antisense to open reading frames and should facilitate systematic and minimally-invasive analysis of gene functions

Optimization of in vivo activity of a bifunctional homing endonuclease and maturase reverses evolutionary degradation

The LAGLIDADG homing endonuclease (LHE) I-AniI has adopted an extremely efficient secondary RNA splicing activity that is beneficial to its host, balanced against inefficient DNA cleavage. A selection experiment identified point mutations in the enzyme that act synergistically to improve endonuclease activity. The amino-acid substitutions increase target affinity, alter the thermal cleavage profile and significantly increase targeted recombination in transfected cells. The RNA splicing activity is not affected by these mutations. The improvement in DNA cleavage activity is largely focused on one of the enzyme's two active sites, corresponding to a rearrangement of a lysine residue hypothesized to act as a general base. Most of the constructs isolated in the screen contain one or more mutations that revert an amino-acid identity to a residue found in one or more close homologues of I-AniI. This implies that mutations that have previously reduced the endonuclease activity of I-AniI are identified and reversed, sometimes in combination with additional ‘artificial’ mutations, to optimize its in vivo activity

Stable Expression of Antibiotic-Resistant Gene ble from Streptoalloteichus hindustanus in the Mitochondria of Chlamydomonas reinhardtii

The mitochondrial expression of exogenous antibiotic resistance genes has not been demonstrated successfully to date, which has limited the development of antibiotic resistance genes as selectable markers for mitochondrial site-directed transformation in Chlamydomonas reinhardtii. In this work, the plasmid pBSLPNCB was constructed by inserting the gene ble of Streptoalloteichus hindustanus (Sh ble), encoding a small (14-kilodalton) protective protein into the site between TERMINVREP-Left repeats and the cob gene in a fragment of mitochondrial DNA (mtDNA) of C. reinhardtii. The fusion DNA-construct, which contained TERMINVREP-Left, Sh ble, cob, and partial nd4 sequence, were introduced into the mitochondria of the respiratory deficient dum-1 mutant CC-2654 of C. reinhardtii by biolistic particle delivery system. A large number of transformants were obtained after eight weeks in the dark. Subsequent subculture of the transformants on the selection TAP media containing 3 ìg/mL Zeomycin for 12 months resulted in genetically modified transgenic algae MT-Bs. Sequencing and Southern analyses on the mitochondrial genome of the different MT-B lines revealed that Sh ble gene had been integrated into the mitochondrial genome of C. reinhardtii. Both Western blot, using the anti-BLE monoclonal antibody, and Zeomycin tolerance analysis confirmed the presence of BLE protein in the transgenic algal cells. It indicates that the Sh ble gene can be stably expressed in the mitochondria of C. reinhardtii

Loss of the sphingolipid desaturase DEGS1 causes hypomyelinating leukodystrophy.

Sphingolipid imbalance is the culprit in a variety of neurological diseases, some affecting the myelin sheath. We have used whole-exome sequencing in patients with undetermined leukoencephalopathies to uncover the endoplasmic reticulum lipid desaturase DEGS1 as the causative gene in 19 patients from 13 unrelated families. Shared features among the cases include severe motor arrest, early nystagmus, dystonia, spasticity, and profound failure to thrive. MRI showed hypomyelination, thinning of the corpus callosum, and progressive thalamic and cerebellar atrophy, suggesting a critical role of DEGS1 in myelin development and maintenance. This enzyme converts dihydroceramide (DhCer) into ceramide (Cer) in the final step of the de novo biosynthesis pathway. We detected a marked increase of the substrate DhCer and DhCer/Cer ratios in patients' fibroblasts and muscle. Further, we used a knockdown approach for disease modeling in Danio rerio, followed by a preclinical test with the first-line treatment for multiple sclerosis, fingolimod (FTY720, Gilenya). The enzymatic inhibition of Cer synthase by fingolimod, 1 step prior to DEGS1 in the pathway, reduced the critical DhCer/Cer imbalance and the severe locomotor disability, increasing the number of myelinating oligodendrocytes in a zebrafish model. These proof-of-concept results pave the way to clinical translation

Caretaker Brca1: keeping the genome in the straight and narrow

Inheritance of germline BRCA1 mutations is associated with a high risk of breast and ovarian cancers. A multitude of cellular functions has been ascribed to BRCA1, including transcription activation and various aspects of DNA repair. So far, indirect evidence has indicated a role for BRCA1 in the repair of double-strand breaks. Recently, an elegant gene targeting design was used to provide definitive evidence that BRCA1 promotes homologous recombination and limits nonhomologous mutagenic repair processes. This reaffirms the role of BRCA1 as caretaker in preserving genomic integrity

Recognition and cleavage site of the intron-encoded omega transposase.

The optional group I intron of the mitochondrial 21S rRNA gene of Saccharomyces cerevisiae contains a 235-codon-long open reading frame the translation product of which (the omega transposase) catalyzes the formation of a double-strand break within the intron-minus (omega-) copies of the same gene. Purified omega transposase generates in vitro a 4-base-pair staggered cut with 3' hydroxyl overhangs at the exact position where the intron eventually inserts in the gene. Using randomly mutagenized synthetic oligonucleotides, single-base mutants were produced at 21 positions around the cleavage site. Experiments with these oligonucleotides show that the recognition site extends over an 18-base pair-long sequence within which minimal sequence degeneracy is tolerated. The intron-encoded omega transposase is, therefore, one of the most specific restriction endonucleases known to date