Birth and death of gene overlaps in vertebrates

<p>Abstract</p> <p>Background</p> <p>Between five and fourteen per cent of genes in the vertebrate genomes do overlap sharing some intronic and/or exonic sequence. It was observed that majority of these overlaps are not conserved among vertebrate lineages. Although several mechanisms have been proposed to explain gene overlap origination the evolutionary basis of these phenomenon are still not well understood. Here, we present results of the comparative analysis of several vertebrate genomes. The purpose of this study was to examine overlapping genes in the context of their evolution and mechanisms leading to their origin.</p> <p>Results</p> <p>Based on the presence and arrangement of human overlapping genes orthologs in rodent and fish genomes we developed 15 theoretical scenarios of overlapping genes evolution. Analysis of these theoretical scenarios and close examination of genomic sequences revealed new mechanisms leading to the overlaps evolution and confirmed that many of the vertebrate gene overlaps are not conserved. This study also demonstrates that repetitive elements contribute to the overlapping genes origination and, for the first time, that evolutionary events could lead to the loss of an ancient overlap.</p> <p>Conclusion</p> <p>Birth as well as most probably death of gene overlaps occurred over the entire time of vertebrate evolution and there wasn't any rapid origin or 'big bang' in the course of overlapping genes evolution. The major forces in the gene overlaps origination are transposition and exaptation. Our results also imply that origin of overlapping genes is not an issue of saving space and contracting genomes size.</p

Overlapping genes in the human and mouse genomes

<p>Abstract</p> <p>Background</p> <p>Increasing evidence suggests that overlapping genes are much more common in eukaryotic genomes than previously thought. In this study we identified and characterized the overlapping genes in a set of 13,484 pairs of human-mouse orthologous genes.</p> <p>Results</p> <p>About 10% of the genes under study are overlapping genes, the majority of which are different-strand overlaps. The majority of the same-strand overlaps are embedded forms, whereas most different-strand overlaps are not embedded and in the convergent transcription orientation. Most of the same-strand overlapping gene pairs show at least a tenfold difference in length, much larger than the length difference between non-overlapping neighboring gene pairs. The length difference between the two different-strand overlapping genes is less dramatic. Over 27% of the different-strand-overlap relationships are shared between human and mouse, compared to only ~8% conservation for same-strand-overlap relationships. More than 96% of the same-strand and different-strand overlaps that are not shared between human and mouse have both genes located on the same chromosomes in the species that does not show the overlap. We examined the causes of transition between the overlapping and non-overlapping states in the two species and found that 3' UTR change plays an important role in the transition.</p> <p>Conclusion</p> <p>Our study contributes to the understanding of the evolutionary transition between overlapping genes and non-overlapping genes and demonstrates the high rates of evolutionary changes in the un-translated regions.</p

The gene structure and expression of human ABHD1: overlapping polyadenylation signal sequence with Sec12

BACKGROUND: Overlapping sense/antisense genes orientated in a tail-to-tail manner, often involving only the 3'UTRs, form the majority of gene pairs in mammalian genomes and can lead to the formation of double-stranded RNA that triggers the destruction of homologous mRNAs. Overlapping polyadenylation signal sequences have not been described previously. RESULTS: An instance of gene overlap has been found involving a shared single functional polyadenylation site. The genes involved are the human alpha/beta hydrolase domain containing gene 1 (ABHD1) and Sec12 genes. The nine exon human ABHD1 gene is located on chromosome 2p23.3 and encodes a 405-residue protein containing a catalytic triad analogous to that present in serine proteases. The Sec12 protein promotes efficient guanine nucleotide exchange on the Sar1 GTPase in the ER. Their sequences overlap for 42 bp in the 3'UTR in an antisense manner. Analysis by 3' RACE identified a single functional polyadenylation site, ATTAAA, within the 3'UTR of ABHD1 and a single polyadenylation signal, AATAAA, within the 3'UTR of Sec12. These polyadenylation signals overlap, sharing three bp. They are also conserved in mouse and rat. ABHD1 was expressed in all tissues and cells examined, but levels of ABHD1 varied greatly, being high in skeletal muscle and testis and low in spleen and fibroblasts. CONCLUSIONS: Mammalian ABHD1 and Sec12 genes contain a conserved 42 bp overlap in their 3'UTR, and share a conserved TTTATTAAA/TTTAATAAA sequence that serves as a polyadenylation signal for both genes. No inverse correlation between the respective levels of ABHD1 and Sec12 RNA was found to indicate that any RNA interference occurred

Forward vs. reverse genetics: a bovine perspective based on visible and hidden phenotypes of inherited disorders

In modern cattle production, we have seen a negative trend for decades in reproduction while productivity and performance have improved. Although considered genetically complex, part of these fecundity, fertility, and rearing success issues are caused by Mendelian monogenic disorders. Traditionally, such disorders are investigated opportunistically based on their sporadic occurrence and through subsequent targeted analysis of affected individuals. This approach is called the forward genetic approach (FGA). Modern genomic technologies, such as single nucleotide polymorphism (SNP) array genotyping and whole-genome sequencing (WGS), allow for straightforward locus mapping and the identification of candidate causal variants in affected individuals or families. Nevertheless, a major drawback is the arbitrary sampling and availability of well-phenotyped individuals for research, especially for mostly invisible defects affecting fecundity, early embryonic death, and abortions. Therefore, the reverse genetic approach (RGA) is applied to screen for underlying recessive lethal or sub-lethal variants. This approach requires the availability of massive population-wide genomic data. By applying a haplotype screen for a significant deviation of the Hardy-Weinberg equilibrium, genomic regions potentially harboring candidate causal variants are identified. The subsequent generation of WGS data of haplotype carriers allows for the mining for pathogenic variants potentially causing a reduction in homozygosity. In the first part of my thesis, I present 18 successful, 1 inconclusive example, and 1 example addressing co-dominant effects of a known disorder. These FGA analyzes include heritable skin (n=7), bone (n=7), neuromuscular (n=1), eye (n=2), as well as syndromic disorders (n=3) in various European cattle breeds. Missense and frameshift variants in the IL17RA, DSP, and FA2H genes were described in three recessive genodermatoses: immunodeficiency with psoriasis-like skin alterations, syndromic ichthyosis, and ichthyosis congenita, respectively. Hypohidrotic ectodermal dysplasia was described as X-linked disorder that is associated with a gross deletion in the EDA gene. In dominant genodermatoses, a missense variant in COL5A2 was shown to lead to classical Ehlers-Danlos syndrome, an in-frame deletion in KRT5 was shown to cause epidermolysis bullosa simplex, and results of a study using an individual case of juvenile angiomatosis remained inconclusive. A recessive disorder described as hemifacial macrosomia was associated with a missense variant in LAMB1. Chondrodysplasia in a single family was shown to be caused by a de novo mutation in the bull leading to a stop-loss of the gene FGFR3. De novo mutations (missense and large deletions) in the COL2A1 and COL1A1 genes were associated with achondrogenesis type II (bulldog calf syndrome), and osteogenesis imperfecta type II, respectively. Another mutation that we found to affect bone morphology was a trisomy in chromosome 29 leading to proportional dwarfism with facial dysplasia. Congenital neuromuscular channelopathy was for the first time associated with a missense variant in KCNG1. Furthermore, a de novo missense variant in ADAMTSL4 and a recessive missense variant in CNGB3 were shown to cause congenital cataract and achromatopsia, respectively. Additionally, cases of pulmonary hypoplasia and anasarca syndrome were analyzed and shown to be caused by trisomy 20 in two unrelated calves and a recessively inherited missense variant in ADAMTS3. Moreover, the fatal syndromic disorder skeletal-cardo-enteric dysplasia was described to be caused by a de novo missense variant in MAP2K2. Finally, I investigated the effects on blood cholesterol and triglyceride levels of heterozygous carriers of the previously described APOB-related cholesterol deficiency. In the second part of my thesis, I present the outcome of the RGA in four main Swiss populations, that was validated with the SWISScow custom array. In the Brown Swiss dairy population, 72 haplotype regions showed significant depletions in homozygosity. Four of these haplotypes (BH6, BH14, BH24, and BH34) were associated with missense and nonsense variants in different genes (MARS2, MRPL55, CPT1C, and ACSL5, respectively). In the Original Braunvieh population, eight haplotype regions were identified. Candidate causal variants included a missense variant in TUBGCP5 gene associated with haplotype OH2, and a splice site frameshift variant in LIG3 gene associated with haplotype OH4. In the Holstein population, 24 haplotype regions were identified with a significant reduction of homozygosity. Subsequently, four novel candidate variants were proposed: a nonsense variant in KIR2DS1 for haplotype HH13, in-frame deletion in the genes NOTCH3 for HH21 haplotype, and RIOX1 for HH25 haplotype, and finally, a missense variant in PCDH15 for HH35 haplotype. In the Simmental population, eleven haplotype regions were detected. The haplotype SH5 was associated with a frameshift variant in DIS3 gene and the haplotypes SH8 and SH9 with missense variants in the CYP2B6 and NUBPL genes, respectively. For the breeds Brown Swiss, Original Braunvieh, and Holstein, association studies were carried out including traits describing fertility, birth, growth, and survival. Thereby most of the described mentioned haplotypes show additive effects. Regardless of the approach, all the described candidate causal variants can be used as a tool of precision diagnostics and represent a step forward towards personalized medicine in cattle. Furthermore, these variants can be easily genotyped and allow for targeted breeding to reduce the number of risk matings, which would lead to a reduction of affected animals and significant improvement in animal health and welfare

New perspectives of genetic disorders in cattle

In the last decades a negative trend in inbreeding has accompanied the evident improvement in productivity and performance of bovine domestic population, predisposing to the occurrence of recessively inherited disorders. The objectives of this thesis were: a) the study of genetic diseases applying a “forward genetic approach” (FGA); b) the estimation of the prevalence of deleterious alleles responsible for eight recessive disorders in different breeds; c) the collection of well-characterized materials in a Biobank for Bovine Genetic Disorders. The FGA allowed the identification of seven new recessive deleterious variants (Paunch calf syndrome - KDM2B; Congenital cholesterol deficiency - APOB; Ichthyosis congenita - FA2H; Hypotrichosis - KRT71; Hypotrichosis - HEPHL1; Achromatopsia - CNGB3; Hemifacial microsomia – LAMB1) and of seven new de novo dominant deleterious variants (Achondrogenesis type II - two variants in COL2A1; Osteogenesis imperfecta - COL1A1; Skeletal-cardio-enteric dysplasia - MAP2K2; Congenital neuromuscular channelopathy - KGNG1; Epidermolysis bullosa simplex - KRT5; Classical Ehlers-Danlos syndrome - COL5A2) in different breeds, associated with a large spectrum of phenotypes affecting different systems. The FGA was based on the sequence of a clinical, genealogical, gross- and/or histopathological and genomic study. In particular, a WGS trio-approach (patient, dam and sire) was applied. The prevalence of deleterious alleles was calculated for the Pseudomyotonia congenita, Paunch calf syndrome, Hemifacial microsomia, Congenital bilateral cataract, Ichthyosis congenita, Ichthyosis fetalis, Achromatopsia and Hypotrichosis. A particular concern resulted the allelic frequency of 12% for the Paunch calf syndrome in Romagnola cattle. In respect to the Biobank for Bovine Genetic Diseases, biological materials of clinical cases and their available relatives as well as controls used for the allelic frequency estimations were stored at -20 °C. Altogether, around 16.000 samples were added to the biobank

Molecular evolution of equine influenza virus non-structural protein 1

Influenza A viruses (IAVs) are common infections of certain avian reservoir species, and they periodically transfer to mammalian hosts. These cross-species jumps are usually associated with sporadic outbreaks, and on rare occasions lead to the establishment of a lineage in the new host species. The immune pressure exerted by the new host on the emergent virus forces it to evolve and adopt strategies to evade immunity in order to survive in nature. Understanding the biological mechanisms that allow successful inter-species transmission and adaptation to mammals is crucial to develop the theoretical tools required to predict and/or control emergence of new viruses in humans and animals. H3N8 equine influenza virus (EIV) represents an interesting model to study the dynamic of within-host variation of an avian-origin IAV. Indeed, this virus has emerged from birds in 1963 and has circulated in horse populations for more than fifty years despite the availability of vaccines. Evidence of evolution of EIV virulence factor non-structural protein 1 (NS1) also exists. NS1 is the main viral antagonist of the host interferon (IFN) response, and it relies on different strategies for overcoming these responses, which varies depending on the viral strain. While some NS1 proteins effectively block the induction of IFN and IFN stimulated genes (ISGs), others block general gene expression at a post-transcriptional level, and therefore reduce the synthesis of IFN and ISGs indirectly. Importantly, little is known about the contribution of these NS1 functions to EIV infection phenotype and adaptation to horses. In this work, we characterised NS1 proteins spanning the entire EIV lineage and showed that NS1s from different time periods after EIV emergence counteract the IFN response using different and mutually exclusive mechanisms. While EIVs circulating in the early 1960s blocked general gene expression by a NS1-mediated blockade of the cleavage and polyadenylation specificity factor 30 (CPSF30), NS1s from contemporary EIVs specifically inhibit the induction of ISGs by interfering with the JAK/STAT pathway. These contrasting anti-IFN strategies are associated with two mutations that appeared sequentially during EIV evolution, E186K substitution and C-terminal truncation. These changes in NS1 allowed contemporary EIVs to replicate in the presence of high levels of IFN. The results shown here with EIV indicate that the interplay between virus evolution and immune evasion plays a key role in IAV mammalian adaptation