Project description:Changes in gene regulation rapidly accumulate between species and may contribute to reproductive isolation through misexpression of genes in interspecific hybrids. Hybrid misexpression, defined by expression levels outside the range of both parental species, is thought to be a result of cis- and trans-acting regulatory changes that interact in the hybrid, or arise from changes in the relative abundance of various tissues or cell types due to defects in developmental. Here, we show that misexpressed genes in a sterile interspecific Saccharomyces yeast hybrid result from a heterochronic shift in the timing of the normal meiotic gene expression program. By tracking nuclear divisions, we find that S. cerevisiae initiates meiosis earlier than its closest known relative, S. paradoxus, yet both species complete meiosis at the same time. Although the hybrid up- and down-regulates genes in a similar manner to both parents, the hybrid meiotic program occurs earlier than both parents. The timing shift results in a heterochronic pattern of misexpression throughout meiosis I and the beginning of meiosis II. Coincident with the timing of misexpression, we find an increase in the relative abundance of opposing cis and trans-acting changes and compensatory changes, as well as a transition from predominantly trans-acting to cis-acting expression divergence over the course of meiosis. However, misexpression does not appear to be a direct consequence of cis- and trans-acting regulatory divergence. Our results demonstrate that hybrid misexpression in yeast results from a heterochronic shift in the meiotic gene expression program.
Project description:Changes in gene regulation rapidly accumulate between species and may contribute to reproductive isolation through misexpression of genes in interspecific hybrids. Hybrid misexpression, defined by expression levels outside the range of both parental species, is thought to be a result of cis- and trans-acting regulatory changes that interact in the hybrid, or arise from changes in the relative abundance of various tissues or cell types due to defects in developmental. Here, we show that misexpressed genes in a sterile interspecific Saccharomyces yeast hybrid result from a heterochronic shift in the timing of the normal meiotic gene expression program. By tracking nuclear divisions, we find that S. cerevisiae initiates meiosis earlier than its closest known relative, S. paradoxus, yet both species complete meiosis at the same time. Although the hybrid up- and down-regulates genes in a similar manner to both parents, the hybrid meiotic program occurs earlier than both parents. The timing shift results in a heterochronic pattern of misexpression throughout meiosis I and the beginning of meiosis II. Coincident with the timing of misexpression, we find an increase in the relative abundance of opposing cis and trans-acting changes and compensatory changes, as well as a transition from predominantly trans-acting to cis-acting expression divergence over the course of meiosis. However, misexpression does not appear to be a direct consequence of cis- and trans-acting regulatory divergence. Our results demonstrate that hybrid misexpression in yeast results from a heterochronic shift in the meiotic gene expression program. We analyzed three biological replicates of the parental yeast strains, S. cerevisiae and S. paradoxus, and four replicates of their hybrid over four developmental time points. Two hybrid replicates contain MATa from S. cerevisiae and MATalpha from S. paradoxus. The other two hybrid replicates are reciprocal crosses. The developmental time points are T0, which serves as a control, and is the moment cells enter sporulation media. M1 is the beginning of meiosis I. M1/M2 is the overlap of the end of meiosis I and the beginning of meiosis II. M2 is the end of meiosis II.
Project description:We compared the genome-wide expression profiles of two yeast species (S. cerevisiae and S. paradoxus) using a two-species microarray that contain species-specific probes and can thus measure the expression levels of the two species simultaneosly. In Addition, we used the array to measure expression levels of the interspecific hybrid of these yeast species, while discriminating between the alleles that correspond to the two parental species. Comparison of the between-species differences and the within-hybrid allele differences allows us to separate cis from trans effects. Also, comparison of the overall expression in the hybrids (both alleles) with their parental species allows us to analyze hybrid over-expression and under-expression. Keywords: comparative transcriptome analysis, hybrid gene expression
Project description:Hybrid sterility is one of the earliest postzygotic isolating mechanisms to evolve between two recently diverged species. Uncovering the mechanisms of hybrid sterilitynot only provides insight into the origins of species but also potentially revealsnovel causes of intra-species infertility.Here we identify causes underlying hybrid infertilityofSchizosaccharomyces pombeand S. kambucha, two fission yeast species that are 99.5% identical at the nucleotide level.These yeasts mate to form viable diploids that efficiently complete meiosis. However,S. kambucha/S. pombe hybrids generate few viable gametes, most of which are either aneuploid or diploid.We find that chromosomal rearrangements and related recombination defectsare major causes of hybrid infertility. Surprisingly, using experiments in which we eliminate meiotic recombination, we find thatrecombination defects cannot completely explain the hybrid infertility. Instead, we find that a significant fraction of hybrid infertility is caused by the action of at least three distinct meiotic drive alleles, one on each S. kambucha chromosome,that “cheat” to be transmitted to more than half (up to 90%) of viable gametes.Two of these driving lociare linked by a chromosomal translocation and thus constitute a novel type of paired meiotic drive complex. We find that all three S. kambuchadrive loci independently contribute to hybrid infertility by causing nonrandom spore death. This study reveals how quickly multiple barriers to fertility can arise.In addition, it provides further support for models in which genetic conflicts, such as those caused by meiotic drive alleles, can drive speciation.
Project description:Hybrid sterility is one of the earliest postzygotic isolating mechanisms to evolve between two recently diverged species. Uncovering the mechanisms of hybrid sterilitynot only provides insight into the origins of species but also potentially revealsnovel causes of intra-species infertility.Here we identify causes underlying hybrid infertilityofSchizosaccharomyces pombeand S. kambucha, two fission yeast species that are 99.5% identical at the nucleotide level.These yeasts mate to form viable diploids that efficiently complete meiosis. However,S. kambucha/S. pombe hybrids generate few viable gametes, most of which are either aneuploid or diploid.We find that chromosomal rearrangements and related recombination defectsare major causes of hybrid infertility. Surprisingly, using experiments in which we eliminate meiotic recombination, we find thatrecombination defects cannot completely explain the hybrid infertility. Instead, we find that a significant fraction of hybrid infertility is caused by the action of at least three distinct meiotic drive alleles, one on each S. kambucha chromosome,that M-bM-^@M-^\cheatM-bM-^@M-^] to be transmitted to more than half (up to 90%) of viable gametes.Two of these driving lociare linked by a chromosomal translocation and thus constitute a novel type of paired meiotic drive complex. We find that all three S. kambuchadrive loci independently contribute to hybrid infertility by causing nonrandom spore death. This study reveals how quickly multiple barriers to fertility can arise.In addition, it provides further support for models in which genetic conflicts, such as those caused by meiotic drive alleles, can drive speciation. Meiotic DNA double-strand break analysis of Schizosaccharomyces kambucha by immunoprecipitating accumulated Rec12-FLAG covalently linked to DNA (without exogenous crosslinking agent used) following nitrogen starvation .
Project description:We compared the genome-wide expression profiles of two yeast species (S. cerevisiae and S. paradoxus) using a two-species microarray that contain species-specific probes and can thus measure the expression levels of the two species simultaneosly. In Addition, we used the array to measure expression levels of the interspecific hybrid of these yeast species, while discriminating between the alleles that correspond to the two parental species. Comparison of the between-species differences and the within-hybrid allele differences allows us to separate cis from trans effects. Also, comparison of the overall expression in the hybrids (both alleles) with their parental species allows us to analyze hybrid over-expression and under-expression. Keywords: comparative transcriptome analysis, hybrid gene expression We analyzed four conditions (rich media, glycerol, heat shock and TSA). For each conditions, we hybridized the pooled sample of both species dyed with cy3/cy5 and a sample of the hybrid dyed with the alternate fluorescent color. Each experiment was done with 2 biological repeats, except for the rich media experiments done with 4 biological repeats.
Project description:According to Dobzhansky-Muller model, hybrid sterility is a consequence of independent evolution of related taxa resulting in incompatible interaction during gametogenesis of their hybrids. We proposed that asynapsis of heterospecific chromosomes in meiotic prophase provides a general and recurrently evolving trigger for the meiotic arrest of interspecific F1 hybrids. We used genome-wide expression profiling to quantify misexpression of Chr X and Chr Y genes.
Project description:Four hybrid yeast strains isolated from a variety of industrial substrates were hybridized to an array-CGH platform containing probes to query the whole genomes of seven different Saccharomyces species. For most of the strains we found evidence of multiple interspecific hybridization events and multiple introgressed regions. The strains queried were GSY205 (isolated from a cider fermentation), GSY505 (a contaminant from a lager beer fermentation), GSY2232 (a commercial wine yeast strain), and GSY312 (a commercial lager beer strain). Additionally, 3 different rare viable spores derived from laboratory-created interspecific S. cerevisiae-S. bayanus (aka S. uvarum) hybrids were queried, before and after evolution in chemostats, via S. cerevisiae-S. bayanus microarrays.
Project description:Genome rearrangements are associated with eukaryotic evolutionary processes ranging from tumorigenesis to speciation. Such rearrangements are especially common following the shock of interspecific hybridization, and some of these could be expected to have strong selective value. To test this expectation we created de novo interspecific yeast hybrids between two diverged but largely syntenic species, Saccharomyces cerevisiae and S. uvarum, then experimentally evolved them under continuous ammonium limitation. We discovered that a characteristic interspecific genome rearrangement arose multiple times in independently evolved populations. We uncovered nine different breakpoints, all occurring in a ~1 kb region of chromosome 14, and all producing an “interspecific fusion junction” within the MEP2 gene coding sequence, such that the 5’ portion derives from S. cerevisiae and the 3’ portion derives from S. uvarum. In most cases the rearrangements altered both chromosomes, resulting in what can be considered to be an introgression of a several-kb region of S. uvarum into an otherwise intact S. cerevisiae chromosome 14, while the S. uvarum chromosome 14 experienced an interspecific reciprocal translocation at the same breakpoint within MEP2, yielding a chimaeric chromosome. The net result is the presence in the cell of two MEP2 fusion genes having identical breakpoints. Given that MEP2 encodes for a high-affinity ammonium permease, that MEP2 fusion genes arise repeatedly under ammonium-limitation, and that three independent evolved isolates carrying MEP2 fusion genes are each more fit than their common ancestor, the novel MEP2 fusion genes are very likely adaptive under ammonium limitation. Our results suggest that when homoploid hybrids form, the admixture of two genomes enables swift and otherwise unlikely evolutionary innovations. Furthermore, the architecture of the MEP2 rearrangement suggests a model for rapid introgression, a phenomenon seen in numerous eukaryotic phyla, that does not invoke repeated backcrossing to one of the parental species. Nomenclature: GSY86 TimeZeroInoculum = ancestral interspecific hybrid used to inoculate ammonium-limited chemostats into 3 replicate vessels A, B, C. 150gen = various single-clone isolates from 150 generations of evolutions from vessels A, B or C. 200gen = various isolates from 200 generations of evolutions from vessels A, B or C.