Project description:CGH arrays for Smukowski Heil, et al MBE 2017. Hybridization is often considered maladaptive, but sometimes hybrids can invade new ecological niches and adapt to novel or stressful environments better than their parents. The genomic changes that occur following hybridization that facilitate genome resolution and/or adaptation are not well understood. Here, we address these questions using experimental evolution of de novo interspecific hybrid yeast Saccharomyces cerevisiae x Saccharomyces uvarum and their parentals. We evolved these strains in nutrient limited conditions for hundreds of generations and sequenced the resulting cultures to identify genomic changes. Analysis of 16 hybrid clones and 16 parental clones identified numerous point mutations, copy number changes, and loss of heterozygosity events, including species biased amplification of nutrient transporters. We focused on a particularly interesting example, in which we saw repeated loss of heterozygosity at the high affinity phosphate transporter gene PHO84 in both intra- and interspecific hybrids. Using allele replacement methods, we tested the fitness of different alleles in hybrid and S. cerevisiae strain backgrounds and found that the loss of heterozygosity is indeed the result of selection on one allele over the other in both S. cerevisiae and the hybrids. This is an example where hybrid genome resolution is driven by positive selection on existing heterozygosity, and demonstrates that even infrequent outcrossing may have lasting impacts on adaptation.
Project description:Genetic analyses of speciation have focused nearly exclusively on retrospective analyses of reproductive isolation between highly divergent species. Yet, a full understanding of the speciation process must encompass analysis of the consequences of genomic divergence in young lineages still capable of exchanging genes under natural conditions. The accumulation of conditionally neutral genetic variation may lead to the evolution of divergent gene networks. In a hybrid background, such mutations may no longer compensate one another, resulting in the appearance of selectively disadvantageous traits, including disruption of gene expression regulation. Here, we documented genome-wide patterns of gene expression divergence between young lineages of normal and dwarf lake whitefish and their backcross hybrids for which strong, yet incomplete post-zygotic isolation barriers exist. A significant proportion (33%) of backcross hybrids showed developmental abnormalities not seen in parental forms and eventually leading to death. While the transcriptome of parental forms was nearly identical during embryonic development, suggesting a role for stabilizing selection, all hybrids displayed strongly divergent patterns of gene expression. By comparing healthy, surviving hybrids against moribund ones, we observed that over 2000 genes were misregulated in these abnormal embryos. In particular, misregulation was significantly biased towards essential developmental genes which were strongly underexpressed. Furthermore, genes previously documented to be highly transgressive (exaggerated inter-individual variance) were almost invariably underexpressed in hybrids. Our results thus clearly showed a transcriptome-wide signature of hybrid breakdown in young, incipient species and demonstrated a persuasive link between misexpression of essential developmental genes and post zygotic isolation.
Project description:Genetic analyses of speciation have focused nearly exclusively on retrospective analyses of reproductive isolation between highly divergent species. Yet, a full understanding of the speciation process must encompass analysis of the consequences of genomic divergence in young lineages still capable of exchanging genes under natural conditions. The accumulation of conditionally neutral genetic variation may lead to the evolution of divergent gene networks. In a hybrid background, such mutations may no longer compensate one another, resulting in the appearance of selectively disadvantageous traits, including disruption of gene expression regulation. Here, we documented genome-wide patterns of gene expression divergence between young lineages of normal and dwarf lake whitefish and their backcross hybrids for which strong, yet incomplete post-zygotic isolation barriers exist. A significant proportion (33%) of backcross hybrids showed developmental abnormalities not seen in parental forms and eventually leading to death. While the transcriptome of parental forms was nearly identical during embryonic development, suggesting a role for stabilizing selection, all hybrids displayed strongly divergent patterns of gene expression. By comparing healthy, surviving hybrids against moribund ones, we observed that over 2000 genes were misregulated in these abnormal embryos. In particular, misregulation was significantly biased towards essential developmental genes which were strongly underexpressed. Furthermore, genes previously documented to be highly transgressive (exaggerated inter-individual variance) were almost invariably underexpressed in hybrids. Our results thus clearly showed a transcriptome-wide signature of hybrid breakdown in young, incipient species and demonstrated a persuasive link between misexpression of essential developmental genes and post zygotic isolation. Samples of dwarf, normal, backcross-healthy and backcross-moribund were hybridized in a loop design, involving eight biological replicates for the backcross-healthy and backcross-moribund comparison and six for the others. Dye swap was performed between each replicate. As a result, we obtained a final set of 32 microarray slides.
Project description:Hybrids between species contain a mixture of two divergent proteomes, the combination of which may lead to dysfunctional protein-protein interactions. We performed an integrative study on hybrids between the swordtail fishes Xiphophorus malinche and Xiphophorus birchmanni, and found that the combination of X. birchmanni ndufs5 (a nuclear-encoded subunit of mitochondrial Complex I) with X. malinche mtDNA (which codes for multiple Complex I subunits) was lethal. We reasoned that if this lethality was due to dysfunctional protein-protein interactions in Complex I causing improper assembly, then in heterozygotes which possess one functional and one dysfunctional allele, the dysfunctional allele might be more likely to exist in an improperly integrated/folded state, and thus be more likely to be degraded by protein quality control mechanisms. This preferential degradation would be measurable as a bias in the proteome towards the compatible allele of ndufs5, and so we sought to measure the relative abundance of peptides derived from the X. malinche and X. birchmanni alleles of ndufs5 in hybrids heterozygous at ndufs5, with X. malinche ancestry in the mtDNA. Peptides derived from each allele are distinguishable by multiple amino acids, and we used heavy-labeled spike-ins to target multiple ndufs5 peptides from each species in 5 hybrids. We successfully detected one pair of birchmanni/malinche peptides, and compared their relative abundance using peak integration, then compared the ratio to that observed in the heavy-labeled spike-in, for which the true ratio was known. We found that the endogenous peptides were skewed towards the allele from the same species as the mtDNA (X. malinche), consistent with our hypothesis.
Project description:RNA/DNA hybrids form when RNA hybridizes with its template DNA generating a three-stranded structure known as the R-loop. Knowledge of how they form and resolve, and their functional roles are limited. Here, we identified proteins that bind to RNA/DNA hybrids.
Project description:Determining the role of DDX17 in the formation of DNA:RNA-hybrids around active DNA double-strand breaks (DSBs) using DRIP-seq in the damaged induced via AsiSI (DIvA) cell system that induced DSBs at known genomic loci in response to hydroxytamoxifen (OHT) treatment via and AsiSI enzyme fused to an oestrogen receptor. Sequencing was done using either control or DDX17 siRNA, and mock or 4 hours 300nM OHT treatment. Paired-end 150 cycles was completed on an Illumina NextSeq 500 and library prep was completed using the NEB NEBNext Ultra II library prep kit.
Project description:Sex chromosomes and more particularely the X chromosomes are known to have a major effect on hybrid male sterility. In this experiment by making use of the reciprocal hybrids between D. simulans and D. sechellia, we are showing the effect of these chromosomes on gene expression in male hybrids Keywords: X chromosome, hybrid Testes from for days old individuals (D. simulans, D. sechellia, hybrid D. simulans female x D. sechellia male, hybrid D. sechellia female x D. simulans male) were dissected and RNA was extracted and hybridized along with a reference RNA from the whole body of 4 days old D. melanogaster male. Gene expression in hybrids were compared to parental gene expression in order to isolate misexpressed genes in each hybrids. In order to reveal the cross effect misexpressed genes in hybrids were compared to identify genes commonly misexpressed and genes genes misexpressed in only one hybrid.
Project description:Through a two-year field experiment, G70×GDH11 with strong heterosis and K326×GDH11 with weak heterosis were screened out. Transcriptome analyses revealed that 80.89% and 57.28% of the differentially expressed genes (DEGs) in the strong and weak heterosis combinations exhibited an overdominant expression pattern, respectively. The genes that up-regulated the overdominant expression in the strong heterosis hybrids were significantly enriched in the ion homeostasis. Genes involved in K+ transport (KAT1/2, GORK, AKT2 and KEA3), activity regulation complex (CBL-CIPK5/6), and vacuole (TPKs) genes were overdominant expressed in strong heterosis hybrids, which contributed to K+ homeostasis and heterosis in tobacco leaves.
Project description:Despite of the paramount importance of heterosis in agriculture, the molecular mechanisms underlying heterosis remain elusive. Recent studies in Arabidopsis suggested possible involvement of DNA methylation in heterosis. We tested this hypothesis genetically by crossing homozygous mutants in DNA methylation-related genes in the Columbia (Col) ecotype with homozygous mutants in the same DNA methylation-related genes in the C24 ecotype. When genes in the RNA-directed DNA methylation (RdDM) pathway were mutated, the resultant F1 hybrids did not show appreciable loss of best parent heterosis (BPH) performances in early seedling growth. In contrast, mutations in the putative chromatin remodeling protein DECREASE OF DNA METHYLATION 1 (DDM1) caused ddm1-Col like growth pattern of ddm1-F1 hybrids, a mid-parent heterosis (MPH) performance. To understand the underlying molecular mechanisms, we compared the transcriptomes of the parental plants and reciprocal F1 hybrids in the wild type and ddm1 mutant backgrounds, and identified 183 non-additively expressed (NAE) genes, which were functionally enriched in defense response, a group of genes negatively associated with plant size. Interestingly, for the expression levels of the NAE genes, WT-F1 hybrids were enriched in the Golden Ration between mid-parent values (MPVs) and Col parents in WT, but ddm1-F1 hybrids were comparable to ddm1-Col parent in ddm1 mutant, which explained the MPH performance of ddm1-F1 hybrids. DNA methylation analyses revealed only one third of the NAE genes with highly methylated promoters whose expression is negatively associated with DNA methylation of promoters, strongly suggesting that DDM1 regulates heterosis by multiple epigenetic modifications.