Pseudogene

About: Pseudogene is a research topic. Over the lifetime, 5528 publications have been published within this topic receiving 336634 citations. The topic is also known as: Ψ & pseudogenes.

Hypomorphic Mutations in the Gene Encoding a Key Fanconi Anemia Protein, FANCD2, Sustain a Significant Group of FA-D2 Patients with Severe Phenotype

Abstract: FANCD2 is an evolutionarily conserved Fanconi anemia (FA) gene that plays a key role in DNA double-strand–type damage responses. Using complementation assays and immunoblotting, a consortium of American and European groups assigned 29 patients with FA from 23 families and 4 additional unrelated patients to complementation group FA-D2. This amounts to 3%–6% of FA-affected patients registered in various data sets. Malformations are frequent in FA-D2 patients, and hematological manifestations appear earlier and progress more rapidly when compared with all other patients combined (FA–non-D2) in the International Fanconi Anemia Registry. FANCD2 is flanked by two pseudogenes. Mutation analysis revealed the expected total of 66 mutated alleles, 34 of which result in aberrant splicing patterns. Many mutations are recurrent and have ethnic associations and shared allelic haplotypes. There were no biallelic null mutations; residual FANCD2 protein of both isotypes was observed in all available patient cell lines. These analyses suggest that, unlike the knockout mouse model, total absence of FANCD2 does not exist in FA-D2 patients, because of constraints on viable combinations of FANCD2 mutations. Although hypomorphic mutations arie involved, clinically, these patients have a relatively severe form of FA.

Gene duplication and fragmentation in the zebra finch major histocompatibility complex

Abstract: Background: Due to its high polymorphism and importance for disease resistance, the major histocompatibility complex (MHC) has been an important focus of many vertebrate genome projects. Avian MHC organization is of particular interest because the chicken Gallus gallus, the avian species with the best characterized MHC, possesses a highly streamlined minimal essential MHC, which is linked to resistance against specific pathogens. It remains unclear the extent to which this organization describes the situation in other birds and whether it represents a derived or ancestral condition. The sequencing of the zebra finch Taeniopygia guttata genome, in combination with targeted bacterial artificial chromosome (BAC) sequencing, has allowed us to characterize an MHC from a highly divergent and diverse avian lineage, the passerines. Results: The zebra finch MHC exhibits a complex structure and history involving gene duplication and fragmentation. The zebra finch MHC includes multiple Class I and Class II genes, some of which appear to be pseudogenes, and spans a much more extensive genomic region than the chicken MHC, as evidenced by the presence of MHC genes on each of seven BACs spanning 739 kb. Cytogenetic (FISH) evidence and the genome assembly itself place core MHC genes on as many as four chromosomes with TAP and Class I genes mapping to different chromosomes. MHC Class II regions are further characterized by high endogenous retroviral content. Lastly, we find strong evidence of selection acting on sites within passerine MHC Class I and Class II genes. Conclusion: The zebra finch MHC differs markedly from that of the chicken, the only other bird species with a complete genome sequence. The apparent lack of synteny between TAP and the expressed MHC Class I locus is in fact reminiscent of a pattern seen in some mammalian lineages and may represent convergent evolution. Our analyses of the zebra finch MHC suggest a complex history involving chromosomal fission, gene duplication and translocation in the history of the MHC in birds, and highlight striking differences in MHC structure and organization among avian lineages.

Simulating evolution by gene duplication.

Abstract: By considering the recent finding that unequal crossing over and other molecular interactions are contributing to the evolution of multigene families, a model of the origin of repetitive genes was studied by Monte Carlo simulations. Starting from a single gene copy, how genetic systems evolve was examined under unequal crossing over, random drift and natural selection. Both beneficial and deteriorating mutations were incorporated, and the latter were assumed to occur ten times more frequently than the former. Positive natural selection favors those chromosomes with more beneficial mutations in redundant copies than others in the population, but accumulation of deteriorating mutations (pseudogenes) have no effect on fitness so long as there remains a functional gene. The results imply the following: (1) Positive natural selection is needed in order to acquire gene families with new functions. Without it, too many pseudogenes accumulate before attaining a functional gene family. (2) There is a large fluctuation in the outcome even if parameters are the same. (3) When unequal crossing over occurs more frequently, the system evolves more rapidly. It was also shown, under realistic values of parameters, that the genetic load for acquiring a new gene is not as large as J. B. S. Haldane suggested, but not so small as in a model in which a system for selection started from already redundant genes.

Organization, structure and evolution of the CYP2 gene cluster on human chromosome 19.

Abstract: The cytochrome P450 superfamily of mixed-function oxygenases has been extensively studied due to its many critical metabolic roles, and also because it is a fascinating example of gene family evolution. The cluster of genes on human chromosome 19 from the CYP2A, 2B, and 2F subfamilies has been previously described as having a complex organization and many pseudogenes. We describe the discovery of genes from three more CYP2 subfamilies inside the cluster, and assemble a complete map of the region. We comprehensively review the organization, structure, and expression of genes from all six subfamilies. A general hypothesis for the evolution of this complex gene cluster is also presented.