Recessive Lethal Mutations Research Articles

An estimate of the average number of recessive lethal mutations carried by humans.

The effects of inbreeding on human health depend critically on the number and severity of recessive, deleterious mutations carried by individuals. In humans, existing estimates of these quantities are based on comparisons between consanguineous and nonconsanguineous couples, an approach that confounds socioeconomic and genetic effects of inbreeding. To overcome this limitation, we focused on a founder population that practices a communal lifestyle, for which there is almost complete Mendelian disease ascertainment and a known pedigree. Focusing on recessive lethal diseases and simulating allele transmissions, we estimated that each haploid set of human autosomes carries on average 0.29 (95% credible interval [0.10, 0.84]) recessive alleles that lead to complete sterility or death by reproductive age when homozygous. Comparison to existing estimates in humans suggests that a substantial fraction of the total burden imposed by recessive deleterious variants is due to single mutations that lead to sterility or death between birth and reproductive age. In turn, comparison to estimates from other eukaryotes points to a surprising constancy of the average number of recessive lethal mutations across organisms with markedly different genome sizes.

PiRNA-mediated transposon regulation and the germ-line mutation rate in Drosophila melanogaster males

Transposons, especially retrotransposons, are abundant in the genome of Drosophila melanogaster. These mobile elements are regulated by small RNAs that interact with the Piwi family of proteins—the piwi-interacting or piRNAs. The Piwi proteins are encoded by the genes argonaute3 (ago3), aubergine (aub), and piwi. Heterochromatin Protein 1 (HP1), a chromatin-organizing protein encoded by the Suppressor of variegation 205 [Su(var)205] gene, also plays a role in this regulation. To assess the mutational impact of weakening the system for transposon regulation, we measured the frequency of recessive X-linked lethal mutations occurring in the germ lines of males from stocks that were heterozygous for mutant alleles of the ago3, aub, piwi, or Su(var)205 genes. These mutant alleles are expected to deplete the wild-type proteins encoded by these genes by as much as 50%. The mutant alleles of piwi and Su(var)205 significantly increased the X-linked lethal mutation frequency, whereas the mutant alleles of ago3 did not. An increased mutation frequency was also observed in males from one of two mutant aub stocks, but this increase may not have been due to the aub mutant. The increased mutation frequency caused by depleting Piwi or HP1suggests that chromatin-organizing proteins play important roles in minimizing the germ-line mutation rate, possibly by stabilizing the structure of the heterochromatin in which many transposons are situated.

Female house mice avoid fertilization by t haplotype incompatible males in a mate choice experiment.

The t haplotype in house mice is a well-known selfish genetic element with detrimental, nonadditive fitness consequences to its carriers: recessive lethal mutations cause t/t homozygotes to perish in utero. Given the severe genetic incompatibility imposed by the t haplotype, we predict females to avoid fertilization by t haplotype incompatible males. Indeed, some of the strongest evidence for compatibility mate choice is related to the t haplotype in house mice. However, all previous evidence for compatibility mate choice in this system is based on olfactory preference. It is so far unknown how general these preferences are and whether they are relevant in an actual mating context. Here, we assess female compatibility mate choice related to t haplotypes in a setting that – for the first time – allowed females to directly interact and mate with males. This approach enabled us to analyse female behaviour during the testing period, and the resulting paternity success and fitness consequences of a given choice. We show that genetic incompatibilities arising from the t haplotype had severe indirect fitness consequences and t females avoided fertilization by t incompatible males. The results are inconclusive whether this avoidance of t fertilization by t females was caused by pre- or post-copulatory processes.

Genetic tools to improve reproduction traits in dairy cattle.

Fertility is a major concern in the dairy cattle industry and has been the subject of numerous studies over the past 20 years. Surprisingly, most of these studies focused on rough female phenotypes and, despite their important role in reproductive success, male- and embryo-related traits have been poorly investigated. In recent years, the rapid and important evolution of technologies in genetic research has led to the development of genomic selection. The generalisation of this method in combination with the achievements of the AI industry have led to the constitution of large databases of genotyping and sequencing data, as well as refined phenotypes and pedigree records. These resources offer unprecedented opportunities in terms of fundamental and applied research. Here we present five such examples with a focus on reproduction-related traits: (1) detection of quantitative trait loci (QTL) for male fertility and semen quality traits; (2) detection of QTL for refined phenotypes associated with female fertility; (3) identification of recessive embryonic lethal mutations by depletion of homozygous haplotypes; (4) identification of recessive embryonic lethal mutations by mining whole-genome sequencing data; and (5) the contribution of high-density single nucleotide polymorphism chips, whole-genome sequencing and imputation to increasing the power of QTL detection methods and to the identification of causal variants.

Developmental genetics of the mouse t-complex.

The proximal third of mouse chromosome 17 is known as the t-complex. The t-haplotype is a variant form of this region containing four tandem inversions compared with the wild-type t-complex, and thus recombination in heterozygotes of the t-haplotype is strongly suppressed along the entire t-complex region. Within this genetically locked t-haplotype, many mutations related to various interesting phenotypes (e.g., taillessness, transmission ratio distortion, recessive lethality) have accumulated, and many mouse geneticists have been attracted to t-haplotype research. Many recessive lethal mutations known as t-complex lethal mutations have been found, and detailed phenotypic analyses have revealed that the functions of t-lethal genes are related to important developmental events. Therefore, identification of the genes responsible for these lethal mutations may contribute to our understanding of the mechanisms of mammalian development. In this review, I introduce the phenotypes of t-lethal mutations and describe recent findings, including our results regarding the molecular identification of a t-lethal gene.

Sodium Copper Chlorophyllin (SCC) Induces Genetic Damage in Postmeiotic and Somatic Wing Cells of Drosophila melanogaster

There is no apparent evidence to indicate that sodium copper chlorophyllin (SCC) is mutagenic. The aim of the present study was thus to determine the mutagenic effect of SCC, in postmeiotic germ cells of the adult male Drosophila. This investigation was based on the ability to examine whether SCC induced sex-linked recessive lethal mutations (SLRL), as well as the somatic mutation and recombination test (SMART). Four different SCC concentrations were used: 0, 45, 69, 80, and 100 mM. For SLRL, two broods were generated to test sperm and primarily spermatids. Results showed a significant frequency of recessive lethal mutations compared with control sperm cells with SCC at 69, 80, and 100 mM. In contrast, the frequency of somatic mutations rose by 0.21 only with 100 mM of SCC. These findings provide evidence that SCC is a weak mutagen in both cell lines. The differential response may be attributed to repair mechanisms that are active in somatic cells but almost absent in germ cells.

Induction of complete and mosaic sex-linked recessive lethal mutations by cigarette smoke filtrate in Drosophila melanogaster

The genotoxic effects of cigarette smoke filtrate (SF) on the germ-line stages were examined in Drosophila melanogaster using the sex-linked recessive lethal test, which detects a broad spectrum of genetic alterations and proved to show correlations between mutagenicity and carcinogenicity of the tested chemicals. SF was extracted from fiberglass filter cartridges; each used in smoking 15 cigarettes. The proper SF concentrations (0.2 µL) in 0.45% NaCl saline were injected intraperitoneally in 2- to 3-day-old wild-type males, alongside with controls injected with 0.2 µL of saline. The genotoxicity effects of SF were examined in all spermatogenesis stages of treated males. Results showed that SF was toxic with an median lethal dose value of approximately 0.2% and induced significant sterility effects. The mutagenicity of SF (0.2%) was significantly stage specific and induced complete sex-linked recessive lethal mutations in the broods representing the spermatocytes and late and early spermatogonia, and induced mosaic mutations in the untreated progeny in the brood representing late spermatogonia. These results indicated, for the first time, that SF induces mosaic mutations, which could result from DNA instabilities and labile permutations that can be replicated and passed to future generations before being fixed into mutations in the untreated progeny of treated males, or originating from mutations that result in increasing hyperplasia of the gonad that subsequently produce the actual mutations in later cell cycles. Such delayed mutagenic effects of SF indicated that SF and, consequently, cigarette smoking have much greater genotoxicity than what was previously predicted.

Chemical composition, antioxidant and antigenotoxic activities of different fractions of Gentiana asclepiadea L. roots extract.

The aim of this study was to evaluate the antioxidant and antigenotoxic activities of chloroform, ethyl acetate and n-butanol fractions obtained from Gentiana asclepiadea L. roots methanolic extract. The main secondary metabolites sweroside, swertiamarin and gentiopicrine were quantified in G. asclepiadea root extracts using HPLC-DAD analysis. Amount of total phenols, flavonoids, flavonols and gallotannins was also determined. The antigenotoxic potential of extracts from roots of G. asclepiadea was assessed using the standard in vivo procedure for the detection of sex linked recessive lethal mutations in Drosophila melanogaster males treated with ethyl methanesulfonate (EMS). The results showed that the most abundant secoiridoid in G. asclepiadea roots was gentiopicrine and its content in the n-butanol fraction (442.89 mg/g) was the highest. Among all extracts, ethyl acetate fraction showed the highest antioxidant activity, as well as total phenolics (146.64 GAE/g), flavonoids (44.62 RUE/g), flavonols (22.71 RUE/g) and gallotannins (0.99 mg GAE/g) content. All the fractions showed antioxidant activity using in vitro model systems and the results have been correlated with total phenolics, flavonoids, flavonols and gallotannins content. In addition to antioxidant activity, G. asclepiadea root extract fractions possess an antigenotoxic effect against DNA damage induced by alkylation with EMS. The antioxidant activity exhibited by G. asclepiadea depended on the phenolic compounds content of the tested extracts, while there was no significant difference in the antigenotoxic potential between fractions.

Autophagy Induction Is a Tor- and Tp53-Independent Cell Survival Response in a Zebrafish Model of Disrupted Ribosome Biogenesis

Ribosome biogenesis underpins cell growth and division. Disruptions in ribosome biogenesis and translation initiation are deleterious to development and underlie a spectrum of diseases known collectively as ribosomopathies. Here, we describe a novel zebrafish mutant, titania (ttis450), which harbours a recessive lethal mutation in pwp2h, a gene encoding a protein component of the small subunit processome. The biochemical impacts of this lesion are decreased production of mature 18S rRNA molecules, activation of Tp53, and impaired ribosome biogenesis. In ttis450, the growth of the endodermal organs, eyes, brain, and craniofacial structures is severely arrested and autophagy is up-regulated, allowing intestinal epithelial cells to evade cell death. Inhibiting autophagy in ttis450 larvae markedly reduces their lifespan. Somewhat surprisingly, autophagy induction in ttis450 larvae is independent of the state of the Tor pathway and proceeds unabated in Tp53-mutant larvae. These data demonstrate that autophagy is a survival mechanism invoked in response to ribosomal stress. This response may be of relevance to therapeutic strategies aimed at killing cancer cells by targeting ribosome biogenesis. In certain contexts, these treatments may promote autophagy and contribute to cancer cells evading cell death.

The ‘obligate diploid’ Candida albicans forms mating-competent haploids

Candida albicans, the most prevalent human fungal pathogen, is considered to be an obligate diploid that carries recessive lethal mutations throughout the genome. Here we demonstrate that C. albicans has a viable haploid state that can be derived from diploid cells under in vitro and in vivo conditions, and that seems to arise through a concerted chromosome loss mechanism. Haploids undergo morphogenetic changes like those of diploids, including the yeast-hyphal transition, chlamydospore formation and a white-opaque switch that facilitates mating. Haploid opaque cells of opposite mating type mate efficiently to regenerate the diploid form, restoring heterozygosity and fitness. Homozygous diploids arise spontaneously by auto-diploidization, and both haploids and auto-diploids show a similar reduction in fitness, in vitro and in vivo, relative to heterozygous diploids, indicating that homozygous cell types are transient in mixed populations. Finally, we constructed stable haploid strains with multiple auxotrophies that will facilitate molecular and genetic analyses of this important pathogen.

Protective role of methanol extracts of Gentiana asclepiadea L. and G. cruciata L. against genotoxic damage induced by ethyl methanesulfonate

The methanol extracts from the underground and aerial part of the two species of Gentiana genus, Gentiana asclepiadea L. and Gentiana cruciata L. from Serbia, were investigated for their antigenotoxic activity against wellestablished mutagenic agent ethyl methanesulfonate (EMS) using the in vivo sexlinked recessive lethal (SLRL) test on Drosophila melanogaster. For this purpose, three days old Canton S males were treated with the potent mutagen EMS in concentration of 0.75 ppm, alone and combined with methanol extracts obtained from underground or aerial part of G. asclepiadea and G. cruciata in concentration of 5%, separately. Although EMS in concentration of 0.75 ppm increased the mutation frequency in all three broods, post-treatments with methanol extracts obtained from the underground and aerial part of G. asclepiadea and G. cruciata in concentration of 5%, respectively, drastically reduced the frequency of sex-linked recessive lethal mutations induced by EMS. Compared to the sucrose, as a negative control, methanol extract obtained from underground part of G. cruciata showed the most potent antigenotoxic activity. Extracts from the underground and aerial part of the two species of Gentiana genus, G. asclepiadea L. and G. cruciata L. from Serbia used in our experiments showed a clear antimutagenic effect, reducing the frequency of mutations induced by a strong mutagen such as EMS.

A De Novo Case of Floating Chromosomal Polymorphisms by Translocation in Quasipaa boulengeri (Anura, Dicroglossidae)

Very few natural polymorphisms involving interchromosomal reciprocal translocations are known in amphibians even in vertebrates. In this study, thirty three populations, including 471 individuals of the spiny frog Quasipaa boulengeri, were karyotypically examined using Giemsa stain or FISH. Five different karyomorphs were observed. The observed heteromorphism was autosomal but not sex-related, as the same heteromorphic chromosomes were found both in males and females. Our results indicated that the variant karyotypes resulted from a mutual interchange occurring between chromosomes 1 and 6. The occurrence of a nearly whole-arm translocation between chromosome no. 1 and no. 6 gave rise to a high frequency of alternate segregation and probably resulted in the maintenance of the translocation polymorphisms in a few populations. The translocation polymorphism is explained by different frequencies of segregation modes of the translocation heterozygote during meiosis. Theoretically, nine karyomorphs should be investigated, however, four expected karyotypes were not found. The absent karyomorphs may result from recessive lethal mutations, position effects, duplications and deficiencies. The phylogenetic inference proved that all populations of Q. boulengeri grouped into a monophyletic clade. The mutual translocation likely evolved just once in this species and the dispersal of the one karyomorph (type IV) can explain the chromosomal variations among populations.

Effect of phenol inducing antioxidant responsive element on D. melanogaster lifespan

The effect of hydrophilic synthetic antioxidant TS-13 (sodium 3-(3′-tert-butyl-4′-hydroxyphenyl)propyl thiosulfonate) on the lifespan of different lines of Drosophila melanogaster under normal conditions and the survival in the oxidative stress induced by hydrogen peroxide and paraquat were studied. The addition of 1% TS-13 to diets extended the lifespan of males and females of the long-living Canton S line of D. melanogaster, had no effect on the lifespan of short-living Oregon R line and shortened the average lifespan of males of the lgl558OR/Cy line of D. melanogaster containing a heterozygous recessive lethal mutation of tumor suppressor. Under the conditions of oxidative stress induced by hydrogen peroxide, TS-13 increased the survival of Canton S males and Oregon R females; under the action of paraquat, the protective effect of antioxidant was manifested toward Canton S females and Oregon R flies of both sexes. Despite the fact that anti-aging and protective properties of synthetic phenolic antioxidant TS-13 strongly depend on the genotype and gender, under extreme conditions of oxidative stress. its positive effect is pronounced.

Identification of human Myofibril‐inducing RNA

The axolotl, Ambystoma mexicanum, carries a c recessive lethal mutation that prevents normal embryonic heart development. In the heart of mutant embryos, expression of tropomyosin is reduced, the development of cardiac sarcomeres fails and the heart does not contract. Myofibril‐Inducing RNA (MIR) from anterior endoderm of normal axolotl embryos restores expression of tropomysin, promotes the formation of sarcomeric myofibrils and induces heart contractions. RNA from fetal and adult human hearts also rescues the axolotl embryonic mutant hearts. To identify the active RNA(s) in humans, we cloned the human heart RNAs and created a RNA library. Two human RNA clones were found to promote mutant axolotl heart development. The hearts treated with these RNAs beat rhythmically, and immunocytochemistry reveals tropomyosin expression and myofibril organization. The RNAs were sequenced; and interestingly, showed no sequence homology to the axolotl MIR. However, two active portions of the secondary structure of the axolotl MIR revealed significant similarities in secondary structure to the human RNA. We hypothesize that the strikingly similar areas of secondary structure in the human and axolotl RNAs are responsible for the rescue phenomenon in the mutant axolotl hearts and may be essential for normal heart development and cardiac myogenesis in all vertebrates.

Study of genotoxicity and antigenotoxicity of the Cotinus coggygria Scop. methanol extract by Drosophila melanogaster sex-linked recessive lethal test

The genotoxic and antigenotoxic effects of Cotinus coggygria Scop. methanol extract was investigated using the Drosophila sex-linked recessive lethal (or SLRL) test. The results presented here show that the methanol extract of Cotinus coggygria in a concentration of 5% and artificial chemical agent ethyl methanesulfonate EMS (0.75 ppm) induce recessive lethal mutations on X-chromosome on Drosophila melanogaster in all broods (I, II and III). Post-treatment with lower concentration of the methanol extract of Cotinus coggygria (2%) was effective in reducing genotoxicity ofmutagen.

Effect of Phenol Inducing the Antioxidant Responsive Element on Drosophila Melanogaster Lifespan

The effect of hydrophilic synthetic antioxidant TC-13 (3-(3'-tert-butyl-4'-hydroxyphenyl)propylthiosulfonate sodium) inducing the antioxidant-responsive element on the lifespan of Drosophila melanogaster was studied. Addition of 1% TC-13 to diets prolonged the lifespan of long-lived D. melanogaster Canton S strain females and males, but not of short-lived Oregon R insects and reduced the mean lifespan of D. melanogaster males of the lgl558OR/Cy strain containing a recessive lethal mutation of tumor suppressor in the heterozygotic state. The geroprotective effects of TC-13 synthetic phenol antioxidant depended on D. melanogaster genotype and gender.

A U-Shaped Dose–Response Relationship between X Radiation and Sex-Linked Recessive Lethal Mutation in Male Germ Cells ofDrosophila

We reported previously that low-dose X irradiation of DNA repair-proficient immature sperm of wild-type Drosophila melanogaster at a low dose rate (50 mGy/min) resulted in a mutation frequency that was lower than that in the sham-irradiated group. Therefore, a U-shaped dose-response relationship was suggested. Here we show that the dose-response curve is actually U-shaped by carrying out a large-scale sex-linked recessive lethal assay using Drosophila. No reduction of the mutation frequency was observed in a strain mutant for the nucleotide excision repair gene mei-9a (Drosophila homologue of human XPF). Introduction of a chromosome fragment containing mei-9+ into the mei-9a mutant strain restored the reduction of the mutation frequency in the low-dose-irradiated group. These results showed that DNA repair was responsible for the U-shaped dose-response relationship in Drosophila.

The mouse frizzy (fr) and rat ‘hairless’ (frCR) mutations are natural variants of protease serine S1 family member 8 (Prss8)

Please cite this paper as: The mouse frizzy (fr) and rat 'hairless' (fr(CR)) mutations are natural variants of protease serine S1 family member 8 (Prss8). Experimental Dermatology 2010; 19: 527-532. Abstract: We have previously suggested (based on genetic mapping analysis) that the allelic 'fuzzy' and 'hairless' mutations in the rat are likely orthologues of the mouse frizzy mutation (fr). Here, we analysed three large intraspecific backcross panels that segregated for mouse fr to restrict this locus to a 0.6-Mb region that includes fewer than 30 genes. DNA sequencing of one of these candidates known to be expressed in skin, protease serine S1 family member 8 (Prss8), revealed a T to A transversion associated with the fr allele that would result in a valine to aspartate substitution at residue 170 in the gene product. To test whether this missense mutation might be the molecular basis of this frizzy variant, we crossed fr/fr mice with mice that carried a recessive perinatal lethal mutation in Prss8. Hybrid offspring that inherited both fr and the Prss8 null allele displayed abnormal hair and skin, showing that these two mutations are allelic, and suggesting strongly that the T to A mutation in Prss8 is responsible for the mutant frizzy phenotype. Sequence analysis of all Prss8 coding regions in the 'hairless' rat identified a 12-bp deletion in the third exon, indicating that mouse fr and the rat 'hairless' mutations are indeed orthologues. However, this analysis failed to detect any alterations to Prss8 coding sequences in the allelic 'fuzzy' rat variant.

Identification and characterization of a mouse recessive lethal mutation which displays cranial neural tube closure defects

Identification and characterization of a mouse recessive lethal mutation which displays cranial neural tube closure defects

Functional Analysis of saxophone, the Drosophila Gene Encoding the BMP Type I Receptor Ortholog of Human ALK1/ACVRL1 and ACVR1/ALK2

In metazoans, bone morphogenetic proteins (BMPs) direct a myriad of developmental and adult homeostatic events through their heterotetrameric type I and type II receptor complexes. We examined 3 existing and 12 newly generated mutations in the Drosophila type I receptor gene, saxophone (sax), the ortholog of the human Activin Receptor-Like Kinase1 and -2 (ALK1/ACVRL1 and ALK2/ACVR1) genes. Our genetic analyses identified two distinct classes of sax alleles. The first class consists of homozygous viable gain-of-function (GOF) alleles that exhibit (1) synthetic lethality in combination with mutations in BMP pathway components, and (2) significant maternal effect lethality that can be rescued by an increased dosage of the BMP encoding gene, dpp+. In contrast, the second class consists of alleles that are recessive lethal and do not exhibit lethality in combination with mutations in other BMP pathway components. The alleles in this second class are clearly loss-of-function (LOF) with both complete and partial loss-of-function mutations represented. We find that one allele in the second class of recessive lethals exhibits dominant-negative behavior, albeit distinct from the GOF activity of the first class of viable alleles. On the basis of the fact that the first class of viable alleles can be reverted to lethality and on our ability to independently generate recessive lethal sax mutations, our analysis demonstrates that sax is an essential gene. Consistent with this conclusion, we find that a normal sax transcript is produced by saxP, a viable allele previously reported to be null, and that this allele can be reverted to lethality. Interestingly, we determine that two mutations in the first class of sax alleles show the same amino acid substitutions as mutations in the human receptors ALK1/ACVRl-1 and ACVR1/ALK2, responsible for cases of hereditary hemorrhagic telangiectasia type 2 (HHT2) and fibrodysplasia ossificans progressiva (FOP), respectively. Finally, the data presented here identify different functional requirements for the Sax receptor, support the proposal that Sax participates in a heteromeric receptor complex, and provide a mechanistic framework for future investigations into disease states that arise from defects in BMP/TGF-beta signaling.