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Bread wheat inflorescences, or spikes, are characteristically unbranched and normally bear one spikelet per rachis node. Wheat mutants on which supernumerary spikelets (SS) develop are particularly useful resources for work towards understanding the genetic mechanisms underlying wheat inflorescence architecture and, ultimately, yield components. Here, we report the characterization of genetically unrelated mutants leading to the identification of the wheat FRIZZY PANICLE gene, encoding a member of the APETALA2/Ethylene Response Factor (AP2/ERF) transcription factor family, which drives the SS trait in bread wheat. Structural and functional characterization of the three wheat FRIZZY PANICLE homoeologous genes (WFZP) revealed that coding mutations of WFZP-D cause the SS phenotype with the most severe effect when WFZP-D lesions are combined with a frameshift mutation in WFZP-A. We provide WFZP-based resources that may be useful for genetic manipulations with the aim of improving bread wheat yield by increasing grain number.

Specific structures in mRNA can stimulate programmed ribosomal frameshifting (PRF). PRF efficiency can vary enormously between different stimulatory structures, but the features that lead to efficient PRF stimulation remain uncertain. To address this question, we studied the structural dynamics of the frameshift signal from West Nile virus (WNV), which stimulates −1 PRF at very high levels and has been proposed to form several different structures, including mutually incompatible pseudoknots and a double hairpin. Using optical tweezers to apply tension to single mRNA molecules, mimicking the tension applied by the ribosome during PRF, we found that the WNV frameshift signal formed an unusually large number of different metastable structures, including all of those previously proposed. From force-extension curve measurements, we mapped 2 mutually exclusive pathways for the folding, each encompassing multiple intermediates. We identified the intermediates in each pathway from length changes and the effects of antisense oligomers blocking formation of specific contacts. Intriguingly, the number of transitions between the different conformers of the WNV frameshift signal was maximal in the range of forces applied by the ribosome during −1 PRF. Furthermore, the occupancy of the pseudoknotted conformations was far too low for static pseudoknots to account for the high levels of −1 PRF. These results support the hypothesis that conformational heterogeneity plays a key role in frameshifting and suggest that transitions between different conformers under tension are linked to efficient PRF stimulation.

Heterozygous frameshift variants in PLIN1 encoding perilipin-1, a key protein for lipid droplet formation and triglyceride metabolism, have been implicated in familial partial lipodystrophy type 4 (FPLD4), a rare entity with only six families reported worldwide. The pathogenicity of other PLIN1 null variants identified in patients with diabetes and/or hyperinsulinemia was recently questioned because of the absence of lipodystrophy in these individuals and the elevated frequency of PLIN1 null variants in the general population. To reevaluate the pathogenicity of PLIN1 frameshift variants owing to new data obtained in the largest series of patients with FPLD4. We performed histological and molecular studies for patients referred to our French National Reference Center for Rare Diseases of Insulin Secretion and Insulin Sensitivity for lipodystrophy and/or insulin resistance and carrying PLIN1 frameshift variants. We identified two heterozygous PLIN1 frameshift variants segregating with the phenotype in nine patients from four unrelated families. The FPLD4 stereotypical signs included postpubertal partial lipoatrophy of variable severity, muscular hypertrophy, acromegaloid features, polycystic ovary syndrome and/or hirsutism, metabolic complications (e.g., hypertriglyceridemia, liver steatosis, insulin resistance, diabetes), and disorganized subcutaneous fat lobules with fibrosis and macrophage infiltration. These data suggest that some FPLD4-associated PLIN1 variants are deleterious. Thus, the evidence for the pathogenicity of each variant ought to be carefully considered before genetic counseling, especially given the importance of an early diagnosis for optimal disease management. Thus, we recommend detailed familial investigation, adipose tissue-focused examination, and follow-up of metabolic evolution.

The Type VI secretion system (T6SS) mediates toxin delivery into both eukaryotic and prokaryotic cells. It is composed of a cytoplasmic structure resembling the tail of contractile bacteriophages anchored to the cell envelope through a membrane complex composed of the TssL and TssM inner membrane proteins and of the TssJ outer membrane lipoprotein. The C-terminal domain of TssM is required for its interaction with TssJ, and for the function of the T6SS. In Citrobacter rodentium, the tssM1 gene does not encode the C-terminal domain. However, the stop codon is preceded by a run of 11 consecutive adenosines. In this study, we demonstrate that this poly-A tract is a transcriptional slippery site that induces the incorporation of additional adenosines, leading to frameshifting, and hence the production of two TssM1 variants, including a full-length canonical protein. We show that both forms of TssM1, and the ratio between these two forms, are required for the function of the T6SS in C. rodentium. Finally, we demonstrate that the tssM gene associated with the Yersinia pseudotuberculosis T6SS-3 gene cluster is also subjected to transcriptional frameshifting.

Seizures have been reported in two families with myoclonus-dystonia due to epsilon-sarcoglycan ( SGCE ) mutations. We report a Norwegian family with myoclonus-dystonia and epilepsy associated with a novel SGCE mutation. All six manifesting SGCE mutation carriers had myoclonus, and dystonia was present in two patients. Sequencing of the SGCE gene in the proband identified a novel frameshift c.372delG mutation that predicts the amino acid change [p.Lys125SerfsX7] and the formation of a premature stop codon. The mutation segregated with myoclonus-dystonia in the family. The typical motor symptoms were accompanied by generalized seizures in four of six affected mutation carriers. The seizure type included febrile, absence and generalized tonic–clonic seizures. One deceased patient with severe epilepsy and myoclonus could not be tested for the SGCE mutation. Seizures are rarely observed in myoclonus-dystonia patients with SGCE mutations, and may not be a part of the phenotype. The co-occurrence of seizures and myoclonus-dystonia suggests that they are both due to the same underlying SGCE mutation. However, with epilepsy being a relatively common disorder and lack of complete co-segregation in our and previous families, it is possible that some patients suffer from two different genetic disorders. The presence of seizures and EEG abnormalities should not be considered exclusion criteria for the diagnosis of myoclonus-dystonia.

Unraveling the molecular basis of inherited disorders of epithelial fragility has led to understanding of the complex structure and function of keratin intermediate filaments. Keratins are organized as a central α-helical rod domain flanked by nonhelical, variable end domains. Pathogenic mutations in 19 different keratin genes have been identified in sequences corresponding to conserved regions at the beginning and end of the rod. These areas have been recognized as zones of overlap between aligned keratin proteins and are thought to be crucial for proper assembly of keratin intermediate filaments. Consequently, all keratin disorders of skin, hair, nail, and mucous membranes caused by mutations in rod domain sequences are characterized by perinuclear clumping of fragmented keratin intermediate filaments, thus compromising mechanical strength and cell integrity. We report here the first mutation in a keratin gene (KRT1) that affects the variable tail domain (V2) and results in a profoundly different abnormality of the cytoskeletal architecture leading to a severe form of epidermal hyperkeratosis known as ichthyosis hystrix Curth–Macklin. Structural analyses disclosed a failure in keratin intermediate filament bundling, retraction of the cytoskeleton from the nucleus, and failed translocation of loricrin to the desmosomal plaques. These data provide the first in vivo evidence for the crucial role of a keratin tail domain in supramolecular keratin intermediate filament organization and barrier formation.

Craniofrontonasal syndrome (CFNS) is an X-linked malformation syndrome with variable phenotype that is caused by mutations in the ephrin-B1 gene ( EFNB1 ). Over 50% of EFNB1 mutations result in premature termination codons that may elicit mRNA degradation by the nonsense-mediated decay pathway. To assess the effects of various mutations at the transcript level, expression of EFNB1 mRNA was studied by RT-PCR in fibroblast cultures established from CFNS female patients. Compared to the wild-type and two missense mutation alleles, severe depletion of transcripts was observed for mutant alleles harbouring either splice site mutation c.407-2A>T at the exon 2/3 boundary or frameshift mutation c.377_384delTCAAGAAG in exon 2. In contrast, escape from mRNA decay was observed for mutation c.614_615delCT, which generates a premature termination codon close to the 3′-end of the penultimate exon 4 disobeying the ‘50–55 bp’ rule. These results suggest differential degradation of mutant EFNB1 transcripts by the nonsense-mediated mRNA decay pathway. Although the clinical phenotypes of the patients were not highly suggestive of a phenotype–genotype correlation, the two female patients were diagnosed with diaphragmatic hernia harbouring putative ephrin-B1 truncating mutations. Previously, disease manifestation in heterozygous females had been attributed mainly to cellular interference of divergent cell populations expressing wild-type or mutant EFNB1 , depending on the pattern of X-inactivation. Upon clonal expansion of patient cells with either the wild-type or mutant EFNB1 on the active X-chromosome, we were able to separate mutant and wild-type EFNB1 -expressing cells in vitro , further supporting the concept of cellular interference in CFNS.

We examined mismatch repair (MMR)-defective diploid strains of budding yeast grown for ∼160 generations to determine whether decreases in spore viability due to the uncovering of recessive lethal mutations correlated with an increase in gross chromosomal rearrangements (GCRs). No GCRs were detected despite dramatic decreases in spore viability, suggesting that frameshift and/or other unrepaired DNA replication lesions play a greater role than chromosomal instability in decreasing viability in MMR-defective strains.

Combined pituitary hormone deficiency (CPHD) is a rare disorder resulting from an impaired pituitary function due to different causes, characterized by impaired secretion of growth hormone (GH) and one or more of the other anterior pituitary hormones. To date, 16 distinct human Prophet of Pit-1 (Prop1) gene mutations have been identified in patients with CPHD, inducing a phenotype involving GH, follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin and thyroid-stimulating hormone (TSH), and rarely adrenocorticotropic hormone, deficiency. Herein we present two siblings of different sexes from a family with parental consanguinity presenting the 301-302delAG mutation in the Prop1 gene. The female presented failure of growth from the age of 6 years and was treated for 10 years with GH, ending in a final height (standard deviation score) of −0.28. TSH deficiency was manifested after the initiation of GH and was treated with thyroxine while puberty was initiated with conjugated estrogens. The male presented TSH deficiency since childhood, treated with thyroxine, and growth failure at the age of 14 years, treated for a period of 2 years with GH. Puberty was initiated with increasing doses of testosterone, while human chorionic gonadotropin was added in order to achieve increased testicular volume. In conclusion, these two siblings of different sexes with CPHD carrying the 301-302delAG mutation in the Prop1 gene presented a variable phenotype characterized by GH, TSH, LH and FSH deficiency.

X-linked Charcot-Marie-Tooth disease (CMTX) is an inherited demyelinating neuropathy caused by mutations in the gene encoding the gap junction protein connexin32 (Cx32). Despite the identification of over 160 different mutations in the Cx32 coding sequence, it is not known whether the mutations cause the disease manifestations through a loss of Cx32 function or through toxic effects on peripheral nerve. We created transgenic mice with a frameshift mutation at codon 175 (175fs), identified in a large CMTX pedigree. Light microscopic examination of the peripheral nerves from adult transgenic animals showed no pathological features. Western blotting did not show transgenic Cx32 protein in any of the 26 lines, although expression of transgenic messenger RNA was detected by revcrse-transcriptase polymerase chain reaction and by ribonuclease protection assay. Our findings indicate that the 175fs mutation results in a loss of Cx32 function, without additional toxic effects.