Recessive Lethals Research Articles

When a Fly Has to Fly to Reproduce: Selection against Conditional Recessive Lethals in Drosophila

We propose an experimental model suitable for demonstrating allele frequency change in Drosophila melanogaster populations caused by selection against an easily scorable conditional lethal, namely recessive flightless alleles such as apterous and vestigial. Homozygotes for these alleles are excluded from reproduction because the food source used to establish each generation is accessible only by flight. The observed dynamics of flightless-allele frequencies generally follows the theoretically predicted pattern, with slight deviation toward less intense selection. We also suggest observing selection against flight-independent visible marker alleles in the same population as a meaningful comparison. The proposed experiments can easily be scheduled within one semester, and the expected data provide ample opportunities for discussion of quantitative evolutionary patterns.

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.

RADIOSENSITIVITY IN DIFFERENT STAGES OF SPERMATOGENESIS IN DROSOPHILA MELANOGASTER

The male flies of various ages were irradiated with 1150- to 3300-r doses of Co/sup 60/ gamma radiation to elucidate the relative radiosensitivity in different stages of spermatogenesis. This was evaluated by studying the sensitivity pattern for different kinds of mutations, such as visibles, sex- linked lethals, II-III translocations, and induced crossovers in males. A peak in the frequency of recessive sex-linked lethals was observed on day 5 after irradiation, while translocation frequency showed a peak on day 7. The frequency of visibles showed no peak, but the statistical calculation suggested an increase in frequency up to day 5. A period of excessive sterility was observed on days 7 and 8 or days 8 and 9 after irradiation. The first crossovers were observed on day 6 or 7, concurrently with a low fertility but prior to the minimum of fertility. The time required for spermiogenesis should be about 6 to 7 days at 25 deg C in adult males. It was found that the radiosensitivity of fully mature sperms (day 1) was somewhat higher than that of nearly mature sperms (day 2). With further immaturity an increasing sensitivity was obseived for all effects studied up to day 5 or 6.more » However, if sterility is used as a measure of radiation effect, the maximum occurs on days 8 and 9. (TCO)« less

Rates of autosomal recessive lethals after x-ray treatment of spermatogonia and spermatozoa in Drosophila melanogaster.

Rates of autosomal recessive lethals after x-ray treatment of spermatogonia and spermatozoa in Drosophila melanogaster.

Salivary gland analysis and localization of second chromosome recessive lethals obtained after irradiation of spermatogonia and spermatozoa in Drosophila melanogaster.

Salivary gland analysis and localization of second chromosome recessive lethals obtained after irradiation of spermatogonia and spermatozoa in Drosophila melanogaster.

CYTOGENETIC STUDIES OF X-RAY AND INGESTED P32 INDUCED SEX-LINKED RECESSIVE LETHALS IN DROSOPHILA MELANOGASTER

Male flies were either irradiated with 1000 r or fed a sugar solution containing Pa/sup 32/. The latter flies attained an average activity of 75 C. The males were immediately mated with unirradiated females according to the brood pattern technique. Chromosomal aberrations (deletions, translocations, and inversions) were recovered following treatment with either mutagen. The distribution of point mutation lethals induced on the X chromosome by P/sup 32/ was identical to the one found after x-ray treatment. The highest frequency of sex-linked recessive lethals in the P/sup 32/ series was found on days 7 and 8, as compared with day 5 for the x-ray series. The sterile period in the x-ray series following the exhaustive mating system used may be attributed partially to dominant lethals, lack of functional sperm, and to meiotic or mitotic inhibition due to irradiation. P/sup 32/ incorporated into the DNA of mature sperm was recovered 7 to 8 days after a single meal, under conditions of excessive mating, which coincides with maximum genetic effect. Thus the results favor the concept that the period of maximum DNA synthesis corresponds to the period of maximum lethal induction and/or of chromosome breakage. (H.H.D.)

The persistency in experimental populations of second chromosome recessive lethals obtained after irradiation of spermatogonia and spermatozoa in Drosophila melanogaster.

The persistency in experimental populations of second chromosome recessive lethals obtained after irradiation of spermatogonia and spermatozoa in Drosophila melanogaster.

Both the RGS Domain and the Six C-Terminal Amino Acids of Mouse Axin Are Required for Normal Embryogenesis

Axin is a negative regulator of canonical Wnt signaling, which promotes the degradation of beta-catenin, the major effector in this signaling cascade. While many protein-binding domains of Axin have been identified, their significance has not been evaluated in vivo. Here, we report the generation and analysis of mice carrying modified Axin alleles in which either the RGS domain or the six C-terminal amino acids (C6 motif) were deleted. The RGS domain is required for APC-binding, while the C6 motif has been implicated in the activation of c-Jun N-terminal kinase, but is not required for the effects of Axin on the Wnt/beta-catenin pathway, in vitro. Both mutant Axin alleles caused recessive embryonic lethality at E9.5-E10.5, with defects indistinguishable from those caused by a null allele. As Axin-DeltaRGS protein was produced at normal levels, its inability to support embryogenesis confirms the importance of interactions between Axin and APC. In contrast, Axin-DeltaC6 protein was expressed at only 25-30% of the normal level, which may account for the recessive lethality of this allele. Furthermore, many Axin(DeltaC6/DeltaC6) embryos that were heterozygous for a beta-catenin null mutation survived to term, demonstrating that early lethality was due to failure to negatively regulate beta-catenin.

Genetic load in a repeatedly irradiated Drosophila melanogaster population.

A population of Drosophila melanogaster irradiated at an early larval stage in the course of more than one hundred generations with 1120 R, and its non-irradiated control population with the same isogenic background, were investigated. The frequency of the second chromosome recessive lethals as well as with their allelism and the viability of individual chromosomes when homozygous and heterozygous were analysed. In some respects considerable differences were established between the two populations. The irradiated population had a higher frequency of lethals and a different distribution of viability of homozygous, lethal-free chromosomes than the control. However, the frequency of allelism among the lethals was higher in the control population. No effects of dominance of the recessive lethals were detected in the material studied.

Mutagenicity of Bacillus thuringiensis exotoxin

The results of four submammalian tests indicate a slight mutagenic activity in two test types of the heat-stable exotoxin produced by Bacillus thuringiensis, serotype 1. No definite clastogenic findings were made; instead, various other C-mitotic effects and chromatin pulverization were observed in concentrations higher than 10% of the autoclaved supernatant of serotype 1 in root tips of Allium. A significant (P=0.0104) increase in the frequency of X-linked recessive lethals among the offspring of Drosophila males reared in 1% medium of serotype 1 supernatant suggested the mutagenic potential of exotoxin. However, no induction of sex chromosomal non-disjunctions were observed in the same Drosophila males. Also tests with the yeast Saccharomyces cerevisae able to detect mitotic recombination induction proved to be negative.

Divergent Evolution of Duplicate Genes Leads to Genetic Incompatibilities Within A. thaliana

Genetic incompatibilities resulting from interactions between two loci represent a potential source of postzygotic barriers and may be an important factor in evolution when they impair the outcome of interspecific crosses. We show that, in crosses between strains of the plant Arabidopsis thaliana, loci interact epistatically, controlling a recessive embryo lethality. This interaction is explained by divergent evolution occurring among paralogs of an essential duplicate gene, for which the functional copy is not located at the same locus in different accessions. These paralogs demonstrate genetic heterogeneity in their respective evolutionary trajectories, which results in widespread incompatibility among strains. Our data suggest that these passive mechanisms, gene duplication and extinction, could represent an important source of genetic incompatibilities across all taxa.

Deletion of eIF2beta suppresses testicular cancer incidence and causes recessive lethality in agouti-yellow mice

The agouti-yellow (A(y)) deletion is the only genetic modifier known to suppress testicular germ cell tumor (TGCT) susceptibility in mice or humans. The A(y) mutation deletes Raly and Eif2s2, and induces the ectopic expression of agouti, all of which are potential TGCT-modifying mutations. Here we report that the reduced TGCT incidence of heterozygous A(y) males and the recessive embryonic lethality of A(y) are caused by the deletion of Eif2s2, the beta subunit of translation initiation factor eIF2. We found that the incidence of affected males was reduced 2-fold in mice that were partially deficient for Eif2s2 and that embryonic lethality occurred near the time of implantation in mice that were fully deficient for Eif2s2. In contrast, neither reduced expression of Raly in gene-trap mice nor ectopic expression of agouti in transgenic or viable-yellow (A(vy)) mutants affected TGCT incidence or embryonic viability. In addition, we provide evidence that partial deficiency of Eif2s2 attenuated germ cell proliferation and differentiation, both of which are important to TGCT formation. These results show that germ cell development and TGCT pathogenesis are sensitive to the availability of the eIF2 translation initiation complex and to changes in the rate of translation.

γTub23CInteracts Genetically With Brahma Chromatin-Remodeling Complexes inDrosophila melanogaster

The brahma gene encodes the catalytic subunit of the Drosophila melanogaster BRM chromatin-remodeling complexes. Screening for mutations that interact with brahma, we isolated the dominant-negative Pearl-2 allele of gammaTub23C. gammaTub23C encodes one of the two gamma-tubulin isoforms in Drosophila and is essential for zygotic viability and normal adult patterning. gamma-Tubulin is a subunit of microtubule organizer complexes. We show that mutations in lethal (1) discs degenerate 4, which encodes the Grip91 subunit of microtubule organizer complexes, suppress the recessive lethality and the imaginal phenotypes caused by gammaTub23C mutations. The genetic interactions between gammaTub23C and chromatin-remodeling mutations suggest that gamma-tubulin might have a role in regulating gene expression.

QTL mapping of inbreeding‐related cold sensitivity and conditional lethality in Drosophila melanogaster

Inbreeding depression is a central theme within genetics, and is of specific interest for researchers within evolutionary and conservation genetics and animal and plant breeding. Inbreeding effects are thought to be caused by the joint expression of conditional and unconditional deleterious alleles. Whenever the expression of deleterious alleles is conditional, this can result in extreme environmental sensitivity in certain inbred lineages. Analysis of conditional lethal effects can reveal some of the loci that are sensitive to inbreeding. We performed a QTL (quantitative trait locus) mapping study of inbreeding-related and conditionally expressed lethality in Drosophila melanogaster. The lethal effect was triggered by exposure to a cold shock. We used a North Carolina crossing Design 3 to establish the mapping population, as well as to estimate the average dominance ratio and heritability. We found two QTL on the major autosomes carrying recessive lethals that caused male mortality, one of which also affected female mortality. More detailed study of these loci will provide information on the mechanistic basis and environmental sensitivity of inbreeding depression.

Consanguineous marriages and endemic malaria: can inbreeding increase population fitness?

BackgroundThe practice of consanguineous marriages is widespread in countries with endemic malaria. In these regions, consanguinity increases the prevalence of α+-thalassemia, which is protective against malaria. However, it also causes an excessive mortality amongst the offspring due to an increase in homozygosis of recessive lethal alleles. The aim of this study was to explore the overall effects of inbreeding on the fitness of a population infested with malaria.MethodsIn a stochastic computer model of population growth, the sizes of inbred and outbred populations were compared. The model has been previously validated producing results for inbred populations that have agreed with analytical predictions. Survival likelihoods for different α+-thalassemia genotypes were obtained from the odds of severe forms of disease from a field study. Survivals were further estimated for different values of mortality from malaria.ResultsInbreeding increases the frequency of α+-thalassemia allele and the loss of life due to homozygosis of recessive lethal alleles; both are proportional to the coefficient of inbreeding and the frequency of alleles in population. Inbreeding-mediated decrease in mortality from malaria (produced via enhanced α+-thalassemia frequency) mitigates inbreeding-related increases in fatality (produced via increased homozygosity of recessive lethals). When the death rate due to malaria is high, the net effect of inbreeding is a reduction in the overall mortality of the population.ConclusionConsanguineous marriages may increase the overall fitness of populations with endemic malaria.

Genotoxicity of paracetamol on the germ cells of Drosophilla melanogaster

Paracetamol is a common analgesic and antipyretic drug. The aim of the present study is to determine the potential genetic effects of Paracetamol in Drosophilla melanogaster using two methods: Sex Linked Recessive Lethals (SLRL) test and effect of Paracetamol on enzyme activity using spectrophotometric analysis. Three concentrations of drug were used (5, 10, and 20 mM). The results reveal significant differences in S.L.R.L, except spermatozoa stages showed insignificant increases when the data of the four broods were considered all together in three treatments. Meanwhile, Paracetamol showed a genotoxic effects in the three categories of the two generations of S.L.R.L, F1 heterozygous females, F2 bar eye females and F2 wild type males on the genetic back ground of Cholinesterase in all treatments.

RAB23 Mutations in Carpenter Syndrome Imply an Unexpected Role for Hedgehog Signaling in Cranial-Suture Development and Obesity

Carpenter syndrome is a pleiotropic disorder with autosomal recessive inheritance, the cardinal features of which include craniosynostosis, polysyndactyly, obesity, and cardiac defects. Using homozygosity mapping, we found linkage to chromosome 6p12.1-q12 and, in 15 independent families, identified five different mutations (four truncating and one missense) in RAB23, which encodes a member of the RAB guanosine triphosphatase (GTPase) family of vesicle transport proteins and acts as a negative regulator of hedgehog (HH) signaling. In 10 patients, the disease was caused by homozygosity for the same nonsense mutation, L145X, that resides on a common haplotype, indicative of a founder effect in patients of northern European descent. Surprisingly, nonsense mutations of Rab23 in open brain mice cause recessive embryonic lethality with neural-tube defects, suggesting a species difference in the requirement for RAB23 during early development. The discovery of RAB23 mutations in patients with Carpenter syndrome implicates HH signaling in cranial-suture biogenesis--an unexpected finding, given that craniosynostosis is not usually associated with mutations of other HH-pathway components--and provides a new molecular target for studies of obesity.

The xbp-1 gene is essential for development in Drosophila

We report in this paper the characterization of Dxbp-1, the Drosophila homologue of the xpb-1 gene that encodes a "bZIP"-containing transcription factor that plays a key role in the unfolded protein response (UPR), an evolutionarily conserved signalling pathway activated by an overload of misfolded proteins in the endoplasmic reticulum (ER). Dxbp-1 is ubiquitously transcribed, and high levels are found in embryonic salivary glands and in the ovarian follicle cells committed to the synthesis of the respiratory appendages. Loss of function of Dxbp-1 induced a recessive larval lethality, thus, revealing an essential requirement for this gene. The Dxbp-1 transcript was submitted to an "unconventional" splicing that generated a processed Dxbp-1s transcript encoding a DXbp-1 protein isoform, as is the case for yeast, Caenorhabditis elegans and vertebrate hac1/xbp-1 transcripts after UPR activation. However, in the absence of exogenously induced ER stress, the Dxbp-1s transcript was also detectable not only throughout embryonic and larval development but also in adults with a high level of accumulation in the male sexual apparatus and, to a lesser extent, in the salivary glands of the third-instar larvae. Using a Dxbp-1:GFP transgene as an in vivo reporter for Dxbp-1 mRNA unconventional splicing, we confirmed that Dxbp-1 processing took place in the salivary glands of the third-instar larvae. The Dxbp-1 gene appears, thus, to play an essential role during the development of Drosophila, hypothetically by stimulating the folding capacities of the ER in cells committed to intense secretory activities.

Mapping of Rym16 Hb , the second soil-borne virus-resistance gene introgressed from Hordeum bulbosum

Rym16(Hb), a gene conferring resistance to soil-borne viruses, was introgressed from Hordeum bulbosum to barley chromosome 2HL. Mechanical inoculation with BaMMV and field tests on a plot contaminated with different viruses demonstrated that Rym16(Hb) is effective against all European viruses of the soil-borne virus complex (BaMMV, BaYMV-1, -2). Genetic analysis revealed a dominant inheritance of the resistance controlled by Rym16(Hb). Using 2HL anchor markers, the size of the introgression was estimated to be about 30 M. In its proximal part, the introgression was characterized by a rearrangement of markers Xbcd266, ABC153 and ABC252, accompanied with pronounced linkage drag by factor 4 in segregating mapping populations. The introgression was found to be associated with a recessive lethality factor, l(Hb), which was closely linked to the markers mentioned above. Recombination occurring within the introgressed H. bulbosum segment allowed us to separate l(Hb) from Rym16(Hb) and to reduce the size of the introgression to 23 cM or less.

Genes in conflict: the biology of selfish genetic elements

Genes in conflict: the biology of selfish genetic elements