Scholarly Literature

This is a database of scholarly literature that concentrates currently on natural and engineered selfish genetic elements (gene drives).  The latest are shown here.
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Analysis of two additional loci in Neurospora crassa related to Spore killer-2

4319
Turner, BC,  Fungal Genetics and Biology,  39:142-150. 2003-01-17 00:00:00.
Two new loci found in one strain of Neurospora crassa (P2604) collected in Malaya are related to the meiotic drive system Spore killer Sk-2. Sk-2 was found in Neurospora intermedia and introgressed into N. crassa. P2604 showed high resistance to killing when crossed to Sk-2. This resistance was found to be linked to, but not allelic to, resistance locus r(Sk-2) on LGIIIL. Analysis showed that the high resistance phenotype of P2604 requires resistance alleles at two different loci on LGIIIR. Strains carrying a resistance allele at only the proximal or the distal locus, respectively, were obtained and intercrossed. Highly resistant strains were obtained by rejoining the two genes. The proximal locus alone confers a low level of resistance. This locus was named pr(Sk-2) for partial resistance to Sk-2. The distal locus was named mod(pr) because its only known phenotype is to modify pr(Sk-2). (C) 2003 Elsevier Science (USA). All rights reserved.

Common features of segregation distortion in plants and animals

4318
Taylor, DRI, P. K.,  Genetica,  117:27-35. 2003-01-16 00:00:00.
Segregation distortion is increasingly recognized as a potentially powerful evolutionary force. This runs counter to the perception that non-Mendelian genes are rare genetic curiosities, a view that seems to be supported by the near ubiquity of the Mendelian system of inheritance. There are several reasons why segregation distortion may be more important than is evidenced by known empirical examples. One possibility is that the types of segregation distorters we have found are only a subset of a broader range of non-Mendelian systems, many of which go undetected. In this paper, we review what is known about the sex-linked meiotic drive system in the plant, Silene latifolia, and present some data on the mechanism of segregation distortion. We outline the general features that segregation distorters in plants and animals have in common. In some cases, such as the paucity of systems that directly alter meiotic segregation, there are likely to be inherent constraints on the range of systems that can possibly occur. Other generalities, however, support the notion that many forms of meiotic drive are possible, and that the known examples of segregation distortion are likely to be only subset of those that can possibly occur. Non-Mendelian genes may therefore have greater evolutionary importance than their current abundance in nature would suggest.

Genetic dissection of hybrid incompatibilities between Drosophila simulans and D-mauritiana. III. Heterogeneous accumulation of hybrid incompatibilities, degree of dominance, and implications for Haldane’s rule

4317
Tao, YH, D. L.,  Evolution,  57:2580-2598. 2003-01-15 00:00:00.
The genetic basis of Haldane's rule was investigated through estimating the accumulation of hybrid incompatibilities between Drosophila simulans and D. mauritiana by means of introgression. The accumulation of hybrid male sterility (HMS) is at least 10 times greater than that of hybrid female sterility (HFS) or hybrid lethality (HL). The degree of dominance for HMS and HL in a pure D. simulans background is estimated as 0.23-0.29 and 0.33-0.39, respectively; that for HL in an F-1 background is unlikely to be very small. Evidence obtained here was used to test the Turelli-Orr model of Haldane's rule. Composite causes, especially, faster-male evolution and recessive hybrid incompatibilities, underlie Haldane's rule in heterogametic male taxa such as Drosophila (XY male and XX female). However, if faster-male evolution is driven by sexual selection, it contradicts Haldane's rule for sterility in heterogametic-female taxa such as Lepidoptera (ZW female and ZZ male). The hypothesis of a faster-heterogametic-sex evolution seems to fit the current data best. This hypothesis states that gametogenesis in the heterogametic sex, instead of in males per se, evolves much faster than in the homogametic sex, in part because of sex-ratio selection. This hypothesis not only explains Haldane's rule in a simple way, but also suggests that genomic conflicts play a major role in evolution and speciation.

Meiotic drive – Bickering genes shape evolution – Not all genes follow the rules of inheritance; now researchers are discovering how organisms adapt to the troublemakers

4316
Pennisi, E,  Science,  301:1837-1839. 2003-01-14 00:00:00.
Reproduction is supposed to be an equal opportunity event. Consider humans: In developing sperm, the sex chromosomes sort 50:50 such that half the sperm carry the male-defining Y chromosome and the rest sport an X. Only the randomness of fertilization leads to families of nine girls and no boys, for example. The same supposedly holds true for the rest of the genome. But in humans, flies, mice, and perhaps many other organisms, guerrilla warfare within the genome sometimes pits one element against another. This often takes on the appearance of a battle between the sexes, but it is really a fight between genes. In this struggle, typically one or more of the X chromosome’s genes strike out against the Y’s genes. Genes on other chromosomes also can get caught up in this struggle, causing an escalating arms race.

The aging effect in the segregation distorter system of Drosophila melanogaster

4315
Oh, SCN, J. G.,  Korean Journal of Genetics,  25:237-242. 2003-01-13 00:00:00.
The SD/SD+ heterozygous male of Drosophila melanogaster transmits the SD second chromosome to its progeny in excess of the Mendelian frequency of 0.5. The k value is defined as the frequency of the SD chromosome recovered among progeny from such a male. This value has been shown to be affected by the age of the male parent: it tends to decrease with increasing age of the parental male, and this aging effect is heritable. The present study indicates that there is a genotypic condition in which the effect of male age is to increase the k value, and this increase is heritable. Thus, a heritable aging effect can occur in both increasing and decreasing the k values, depending upon the genotypes.

Transmission ratio distortion in mice

4314
Lyon, MF,  Annual Review of Genetics,  37:393-408. 2003-01-12 00:00:00.
The most studied example of transmission ratio distortion (TRD) in mice is that of the t-complex. This is a variant-region of Chromosome 17 which exists as a polymorphism in wild mice. Males heterozygous for a t-haplotype and a normal Chr 17 transmit-the t haplotype to >50% of their young, up to 99%.- Homozygous males are-sterile. The TRD produced by-the t-complex, is due to the action of three or more distorter genes (Tcd) on a responder. gene (Tcr). t-Haplotypes are maintained intact by crossover suppression induced by four neighboring inversions, the Tcd and by Tcr loci lying in different inversions. Sperm formation is normal in t/t males, but sperm function is impaired through gross defects in sperm motility. The responder gene has been identified as a fusion gene formed from a sperm motility kinase and a ribosomal S6 kinase. Three candidate distorter genes have also been identified as genes coding for dynein chains, and thus possibly involved in sperm flagellar function.

Closing the (Ran)GAP on segregation distortion in Drosophila

4313
Kusano, AS, C.; Chan, H. Y. E.; Ganetzky, B.,  Bioessays,  25:108-115. 2003-01-11 00:00:00.
Segregation Distorter (SD) is a meiotic drive system in Drosophila that causes preferential transmission of the SD chromosome from SD/SD+ males owing to induced dysfunction of SD+ spermatids. Since its discovery in 1956, SD and its mode of action have baffled biologists. Recently, substantial progress has been made in elucidating this puzzle. Sd, the primary gene responsible for distortion encodes a mutant RanGAP, a key protein in the Ran signaling pathway required for nuclear transport and other nuclear functions. The mutant protein is enzymatically active but mislocalized to nuclei, which apparently disrupts Ran signaling by reducing intranuclear Ran-GTP levels. Some evidence suggests that a defect in nuclear transport may be the main cause of sperm dysfunction. Although important questions remain, the basic mechanism of distortion is now understood sufficiently well that specific hypotheses can be formulated and tested. This previously mysterious genetic system may now offer unique insights into novel aspects of regulation by Ran. (C) 2003 Wiley Periodicals, Inc.

B chromosomes in plants: escapees from the A chromosome genome?

4312
Jones, NH, A.,  Trends in Plant Science,  8:417-423. 2003-01-10 00:00:00.
B chromosomes are dispensable elements that do not recombine with the A chromosomes of the regular complement and that follow their own evolutionary track. In some cases, they are known to be nuclear parasites with autonomous modes of inheritance, exploiting 'drive' to ensure their survival in populations. Their I selfishness' brings them into conflict with their host nuclear genome and generates a host-parasite relationship, with anti-B-chromosome genes working to ameliorate the worst of their excesses in depriving their hosts of genetic resources. Molecular studies are homing in on their sequence organization to give us an insight into the origin and evolution of these enigmatic chromosomes, which are, with rare exceptions, without active genes.

Responder (Rsp) alleles in the Segregation Distorter (SD) system of meiotic drive in Drosophila may represent a complex family of satellite repeat sequences

4311
Houtchens, KL, T. W.,  Genetica,  117:291-302. 2003-01-09 00:00:00.
In D. melanogaster males carrying Segregation Distorter (SD) second chromosomes, sperm receiving sensitive alleles of the Responder (Rsp) locus are subject to high rates of dysfunction. The Rsp region is located in 2R immediately adjacent to the centromere in heterochromatic band 39, and covers roughly 600 kb of material, of which approximately 85 kb is comprised of several hundred copies of a 240-bp satellite DNA sequence. Cytological observations as well as molecular analysis of rearrangements which bisect h39 indicate that sensitivity of the Rsp target to SD action is also subdivisible, and sensitivities of the component pieces appear to be correlated with copy number of the 240 bp repeat. In an attempt to examine possible higher order sequence structure for these blocks, PCR using single primers derived from a canonical repeat was used to identify potential reversals of direction of tandem arrays; that is, head-to-head or tail-to-tail junctions. Surprisingly, for two different Rsp alleles, only a single such reversal product for each was identified, differing in size and sequence between alleles. Sequencing of PCR products identified diverged copies of the canonical repeats that would not have been found using the levels of DNA stringency employed in earlier studies. Examination of Southern digests and slot-blots for DNA quantification indicates that adding the estimated numbers of such diverged copies to the canonical repeat copies discovered earlier is potentially sufficient to account for the entire 600 kb Rsp region. This adds strength to the hypothesis that this extended family of repeats is in fact the target of SD-mediated sperm dysfunction. Implications of these results for understanding the evolution of repetitive DNA are also discussed.

General principles for risk assessment of living modified organisms: Lessons from chemical risk assessment

4310
Hill, RAS, C.,  Environ. Biosafety Res,  2:81-88. 2003-01-08 00:00:00.
Modern biotechnology has led to the development and use of Living Modified Organisms (LMOs) for agriculture and other purposes. Regulators at the national level are increasingly depending on risk assessment as a tool for assessing potential adverse effects of LMOs on the environment and human health. In addition, the Cartagena Protocol on Biosafety, an international agreement expected to enter into force in the near future, requires risk assessment as the basis for decision-making regarding import of some LMOs. While LMO risk assessment is relatively new, there are other risk assessment disciplines which have developed over longer time periods. The field of assessment of the environmental and human health risks of chemicals is particularly well developed, and is similar in application to LMO risk assessment. This paper aims to draw lessons for LMO risk assessment from the vast experience with chemical risk assessment. Seven general principles are outlined which should serve as a useful checklist to guide assessments of risks posed by LMOs.

Four loci on abnormal chromosome 10 contribute to meiotic drive in maize

4309
Hiatt, END, R. K.,  Genetics,  164:699-709. 2003-01-07 00:00:00.
We provide a genetic analysis of the meiotic drive system on maize abnormal chromosome 10 (Ab10) that causes preferential segregation of specific chromosomal regions to the reproductive megaspore. The data indicate that at least four chromosomal regions contribute to meiotic drive, each providing distinct functions that can be differentiated from each other genetically and/or phenotypically. Previous reports established that meiotic drive requires neocentromere activity at specific tandem repeat arrays (knobs) and that two regions on Ab10 are involved in trans-activating neocentromeres. Here we confirm and extend data suggesting that only one of the neocentromere-activating regions is sufficient to move many knobs. We also confirm the localization of a locus/loci on Ab10, thought to be a prerequisite for meiotic drive, which promotes recombination in structural heterozygotes. In addition, we identified two new and independent functions required for meiotic drive. One was identified through the characterization of a deletion derivative of Ab10 [Df(L)] and another as a newly identified meiotic drive mutation (suppressor Of meiotic drive 3). In the absence of either function, meiotic drive is abolished but neocentromere activity and the recombination effect typical of Ab10 are unaffected. These results demonstrate that neocentromere activity and increased recombination are not the only events required for meiotic drive.

The meiotic drive system on maize abnormal chromosome 10 contains few essential genes

4308
Hiatt, END, R. K.,  Genetica,  117:67-76. 2003-01-06 00:00:00.
In maize, a distal portion of abnormal chromosome 10 (Ab10) causes the meiotic drive of itself as well as many unlinked heterochromatic regions known as knobs. The Ab10 drive system, which encodes trans- as well as cis-acting components, occupies a large region of chromosome 10L equivalent to similar to3% of the genome. Here we describe five new structural mutations of Ab10 (five deletions and a duplication) that arose from a screen for meiotic drive mutants. The high frequency of breakage events, detected both genetically and cytologically, suggest that the chromosome may be especially unstable. Very large deletions within the drive system are female-transmissible and plants homozygous for deficiencies lacking much of this interval can be grown to maturity. The data suggest that few genes required for normal growth and development lie within the portion of Ab10 responsible for meiotic drive. These and other published data suggest that meiotic drive systems tend to evolve in gene-sparse or otherwise information-poor regions of the genome where they are less likely to negatively affect individual fitness.

Sexual transmission of the Het-s prion leads to meiotic drive in Poldospora anserina

4307
Dalstra, HJPS, K.; Debets, A. J. M.; Saupe, S. J.; Hoekstra, R. F.,  Proceedings of the National Academy of Sciences of the United States of America,  100:6616-6621. 2003-01-05 00:00:00.
In the filamentous fungus Podospora anserina, two phenomena are associated with polymorphism at the het-s locus, vegetative incompatibility and ascospore abortion. Two het-s alleles occur naturally, het-s and het-S. The het-s encoded protein is a prion propagating as a self-perpetuating amyloid aggregate. When prion-infected [Het-s] hyphae fuse with [Het-S] hyphae, the resulting heterokaryotic cells necrotize. [Het-s] and [Het-S] strains are sexually compatible. When, however, a female [Het-s] crosses with [Het-S], a significant percentage of het-S spores abort, in a way similar to spore killing in Neurospora and Podospora. We report here that sexual transmission of the [Het-s] prion after nonisogamous mating in the reproductive cycle of Podospora is responsible for the killing of het-S spores. Progeny of crosses between isogenic strains with distinct wild-type or introduced, ectopic het-s/S alleles were cytologically and genetically analyzed. The effect of het-s/S overexpression, ectopic het-s/S expression, absence of het-s expression, loss of [Het-s] prion infection, and the distribution patterns of HET-s/S-GFP proteins were categorized during meiosis and ascospore formation. This study unveiled a het-S spore-killing system that is governed by dosage of and interaction between the [Het-s] prion and the HET-S protein. Due to this property of the [Het-s] prion, the het-s allele acts as a meiotic drive element favoring maintenance of the prion-forming allele in natural populations.

Site-specific selfish genes as tools for the control and genetic engineering of natural populations

4306
Burt, A,  Proceedings of the Royal Society B-Biological Sciences,  270:921-928. 2003-01-04 00:00:00.
Site-specific selfish genes exploit host functions to copy themselves into a defined target DNA sequence, and include homing endonuclease genes, group II introns and some LINE-like transposable elements. If such genes can be engineered to target new host sequences, then they can be used to manipulate natural populations, even if the number of individuals released is a small fraction of the entire population. For example, a genetic load sufficient to eradicate a population can be imposed in fewer than 20 generations, if the target is an essential host gene, the knockout is recessive and the selfish gene has an appropriate promoter. There will be selection for resistance, but several strategies are available for reducing the likelihood of it evolving. These genes may also be used to genetically engineer natural populations, by means of population-wide gene knockouts, gene replacements and genetic transformations. By targeting sex-linked loci just prior to meiosis one may skew the population sex ratio, and by changing the promoter one may limit the spread of the gene to neighbouring populations. The proposed constructs are evolutionarily stable in the face of the mutations most likely to arise during their spread, and strategies are also available for reversing the manipulations.

Marcus Rhoades, preferential segregation and meiotic drive

4305
Birchler, JAD, R. K.; Doebley, J. F.,  Genetics,  164:835-841. 2003-01-03 00:00:00.
LONG before microarray biologists coined and promoted the term “discovery science,” maize geneticists were avid practitioners of this mode of investigation. In fact, one might say that for a number of years, the field of maize genetics basically operated as discovery science. Many have speculated about why maize remains a model organism for genetic analysis, given its long life cycle relative to other species. It has many virtues, sometimes little understood or appreciated by outsiders, but the maize geneticist’s style of science devoted to discovery and an unusually strong commitment to cooperation probably contributes to this trend. One of the great practitioners of this style of science was Marcus Rhoades (Figure 1), who often advised beginning graduate students: “Just get in the lab and start to work; you can’t help but find something.” “What are the facts?” was his common refrain to model building and theorizing. Along with his penchant for discovery was a dogged experimentalist attack to explore the parameters and dimensions of a new finding.

Overlapping deletions spanning the proximal two-thirds of the mouse t complex

Bergstrom, DEB, R. A.; Munroe, R. J.; Lee, B. K.; Browning, V. L.; You, Y.; Eicher, E. M.; Schimenti, J. C.,  Mammalian Genome,  14:817-829. 2003-01-02 00:00:00.
Chromosome deletion complexes in model organisms serve as valuable genetic tools for the functional and physical annotation of complex genomes. Among their many roles, deletions can serve as mapping tools for simple or quantitative trait loci (QTLs), genetic reagents for regional mutagenesis experiments, and, in the case of mice, models of human contiguous gene deletion syndromes. Deletions also are uniquely suited for identifying regions of the genome containing haploinsufficient or imprinted loci. Here we describe the creation of new deletions at the proximal end of mouse Chromosome (Chr) 17 by using the technique of ES cell irradiation and the extensive molecular characterization of these and previously isolated deletions that, in total, cover much of the mouse t complex. The deletions are arranged in five overlapping complexes that collectively span about 25 Mbp. Furthermore, we have integrated each of the deletion complexes with physical data from public and private mouse genome sequences, and our own genetic data, to resolve some discrepancies. These deletions will be useful for characterizing several phenomena related to the t complex and t haplotypes, including transmission ratio distortion, male infertility, and the collection of t haplotype embryonic lethal mutations. The deletions will also be useful for mapping other loci of interest on proximal Chr 17, including T-associated sex reversal (Tas) and head-tilt (het). The new deletions have thus far been used to localize the recently identified t haplolethal (Thl1) locus to an approximately 1.3-Mbp interval.

Adaptation for horizontal transfer in a homing endonuclease

4323
Koufopanou, VG, M. R.; Burt, A.,  Molecular Biology and Evolution,  19:239-246. 2002-01-21 00:00:00.
Selfish genes of no function other than self-propagation are susceptible to degeneration if they become fixed in a population. and regular transfer to new species may be the only means for their long-term persistence. To test this idea we surveyed 24 species of yeast for VDE, a nuclear. intein-associated homing endonuclease gene (HEG) originally discovered in Saccharomyces cerevisiae. Phylogenetic analyses show that horizontal transmission has been a regular occurrence in its evolutionary history. Moreover, VDE appears to be specifically adapted for horizontal transmission. Its 31-bp recognition sequence is an unusually well-conserved region in an unusually well-conserved gene. In addition, the nine nucleotide sites most critical for homing are also unusually well conserved. Such adaptation for horizontal transmission presumably arose as a consequence of selection, both among HEGs at different locations in the genome and among variant,,, at the same location. The frequency of horizontal transmission must therefore be a key feature constraining the distribution and abundance of these genes.

Reciprocal crossover asymmetry and meiotic drive in a human recombination hot spot

4322
Jeffreys, AJN, R.,  Nature Genetics,  31:267-271. 2002-01-20 00:00:00.
Human DNA diversity arises ultimately from germline mutation that creates new haplotypes that can be reshuffled by meiotic recombination. Reciprocal crossover generates recombinant haplotypes but should not influence the frequencies of alleles in a population. We demonstrate crossover asymmetry at a recombination hot spot in the major histocompatibility complex(1), whereby reciprocal exchanges in sperm map to different locations in the hot spot. We identify a single-nucleotide polymorphism at the center of the hot spot and show that, when heterozygous, it seems sufficient to cause this asymmetry, apparently by influencing the efficiency of highly localized crossover initiation. As a consequence, crossovers in heterozygotes are accompanied by biased gene conversion, most likely occurring by gap repair(2), that can also affect nearby polymorphisms through repair of an extended gap. The result is substantial over-transmission of the recombination-suppressing allele and neighboring markers to crossover products. Computer simulations show that this meiotic drive, although weak at the population level, is sufficient to favor eventual fixation of the recombination-suppressing variant. These findings provide an explanation for the relatively uniform widths of human crossover hot spots and suggest that hot spots may be generally prone to extinction by meiotic drive(3).

X chromosome effect on maternal recombination and meiotic drive in the mouse

4321
de la Casa-Esperon, EL-O, J. C.; de Villena, F. P. M.; Briscoe, T. L.; Malette, J. M.; Vaughan, J. E.; Morgan, K.; Sapienza, C.,  Genetics,  161:1651-1659. 2002-01-19 00:00:00.
We observed that maternal meiotic drive favoring the inheritance of DDK alleles at the Om locus on mouse chromosome 11 was correlated with the X chromosome inactivation phenotype of (C57BL/6Pgk1(a) X DDK)F-1 mothers. The basis for this unexpected observation appears to lie in the well-documented effect of recombination on meiotic drive that results from nonrandom segregation of chromosomes. Our analysis of genome-wide levels of meiotic recombination in females that vary in their X-inactivation phenotype indicates that an allelic difference at an X-linked locus is responsible for modulating levels of recombination in oocytes.

Does Stellate cause meiotic drive in Drosophila melanogaster?

4320
Belloni, MT, P.; Bozzetti, M. P.; Palumbo, G.; Robbins, L. G.,  Genetics,  161:1551-1559. 2002-01-18 00:00:00.
Drosophila melanogaster males deficient for the crystal (cry) locus of the Y chromosome that carry between 15 and 60 copies of the X-linked Stellate (Ste) gene are semisterile, have elevated levels of nondisjunction, produce distorted sperm genotype ratios (meiotic drive), and evince hyperactive transcription of Ste in the testes. Ste seems to be the active element in this system, and it has been proposed that the ancestral Ste gene was "selfish" and increased in frequency because it caused meiotic drive. This hypothetical evolutionary history is based on the idea that Ste overexpression, and not the lack of cry, causes the meiotic drive of cry(-) males. To test whether this is true, we have constructed a Ste-deleted X chromosome and examined the phenotype of Ste(-)/cry(-) males. If hyperactivity of Ste were necessary for the transmission defects seen in cry- males, cry males completely deficient for.Ste would be normal. Although it is impossible to construct a completely Ste(-) genotype, we find that Ste(-)/cry(-) males have exactly the same phenotype as Ste(+)/cry(-) males. The deletion of all X chromosome Ste copies not only does not eliminate meiotic drive and nondisjunction, but it also does not even reduce them below the levels produced when the X carries 15 copies of Ste.

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