Name: how exons mix to form new genes
Uploaded: 2021-04-07T12:11:59.000Z
Duration: 2 min 32 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

Biological Evolution: Unity And Diversity

HS-LS4-1

Exon Recombination

真核生物の遺伝子は、エクソンと呼ばれるタンパク質コード配列とイントロンと呼ばれる非コード配列の交互のブロックで構成されています。
エクソン組換えとは、同じ遺伝子または異なる遺伝子のエクソンが組み換えて、新しいエクソン-イントロン配列の組み合わせを生み出し、それが新しい遺伝子に進化するプロセスです。
エクソン組換えは、非相同組換えまたはレトロ転位によって媒介され得る。
非相同または非違法な組換えの際には、配列の類似性がないDNA鎖が組み換えられ、新しい遺伝子構造が生成されることがあります。
慢性肉芽腫性疾患 - 免疫系の遺伝性疾患が良い例です。この疾患の多くの患者は、酵素NADPHオキシダーゼをコードするphox遺伝子にまれな変異を持っています。
野生型NADPHオキシダーゼは、感染時にスーパーオキシドなどの活性酸素種を産生し、感染性病原体の食細胞を介した殺傷を助けます。
まれに、phox遺伝子のエクソン8とエクソン11の間の非相同配列が組み換えられ、エクソン9とエクソン10の重複を引き起こす。これにより、酵素NADPHオキシダーゼの活性が低下します。障害のある酵素は、細菌感染を取り除くのに十分な活性酸素種を生成できず、肉芽腫またはマクロファージと関連する免疫細胞の凝集を引き起こします。 
レトロトランスポジションによるエクソン組換えは、アフリカのショウジョウバエにおけるJingwei遺伝子の進化を最もよく説明できます。
約250万年前、Adh mRNAの一部がDNAに逆転写され、Ynd遺伝子のエクソンと再結合して、Jingweiと呼ばれる新しい遺伝子が生まれました。
Ynd遺伝子はショウジョウバエの精巣の発達に関与しており、Adh遺伝子はアルコールデヒドロゲナーゼをコードしています。新しい遺伝子Jingweiは、Yndに由来するドメインとAdhに由来するドメインの2つのドメインを持つタンパク質をコードしています。
したがって、タンパク質Jingweiはショウジョウバエの精巣で発現し、ホルモンとフェロモンの生合成に関与しています。

<ol>
	<li>Long, Manyuan, Esther Betrán, Kevin Thornton, and Wen Wang. "The origin of new genes: glimpses from the young and old." Nature Reviews Genetics 4, no. 11 (2003): 865-875.</li>
	<li>Van Rijk, Anke, and Hans Bloemendal. "Molecular mechanisms of exon shuffling: illegitimate recombination." In Origin and Evolution of New Gene Functions, pp. 245-249.スプリンガー、ドルドレヒト、2003年。</li>
	<li>「エクソンシャッフルによるタンパク質の指向性進化」 Nature Biotechnology 19, no. 5 (2001): 423-428.</li>
	<li>「新規遺伝子の進化」 Current opinion in Genetics & Development 11, no. 6 (2001): 673-680.</li>
</ol>

エクソン組み換え

新しい遺伝子の進化は種分化にとって重要です。エクソン組み換えは、エクソンシャッフリングまたはドメインシャッフリングとも呼ばれ、新しい遺伝子形成の重要な手段です。これは脊椎動物、無脊椎動物、さらにジャガイモやヒマワリなどの一部の植物で観察されます。エクソンの組換え中、同じまたは異なる遺伝子のエクソンが組み換えられ、新しいエクソンとイントロンの組み合わせが生成され、新しい遺伝子に進化する可能性があります。

エクソンシャッフリングは「スプライスフレームルール」に従います。各エクソンには3つの読み取りフレームがあります。入ってくるエクソンは、3つの読み取りフレームのいずれかで再結合して結合し、フレームシフト突然変異を引き起こす可能性があります。したがって、すべての組換えイベントが役立つわけではありません。中には、途中で終止コドンや未熟なタンパク質が生成される場合もあります。

ヒトゲノムにおけるエクソンシャッフリング

遺伝子の重複と分岐に加えて、エクソンシャッフリングは、いくつかのヒト固有の遺伝子の進化に起因すると考えられています。例えば、約2,500万年前、初期の霊長類ではMCH（メラニン凝集ホルモン）と呼ばれる遺伝子がレトロトランスポジションによるエクソン組み換えを受けました。これにより新たにイントロンとエクソンの境界が形成され、後にヒト科に特有の保存遺伝子PMCHL1に進化しました。これは偽遺伝子ですが、アンチセンスRNAは人間の脳で発現します。 元のMCH 遺伝子はげっ歯類のエネルギー要求量と体重のバランスに関与する神経ペプチドをコードしているため、PMCHL-1も同様の機能を持つと予想されます。

不正組換え(IR)は、エクソン組換えまたはエクソンシャッフリングの最も一般的に観察されるメカニズムの1つです。IRはエクソンの重複を引き起こします。これは、デュシェンヌ型およびベッカー型筋ジストロフィー、家族性高コレステロール血症、レシュ・ナイハン症候群、血友病、リポタンパク質リパーゼ欠損症などのいくつかのヒトの病気で観察されています。

新しい遺伝子の進化は、種分化にとって重要です。エクソン組換えは、エクソンシャッフルまたはドメインシャッフルとも呼ばれ、新しい...

Education

JoVE Core

Molecular Biology

分子生物学

Unit 2

ユニット2

Genomes and Evolution

ゲノムと進化

KEY TERMS AND CONCEPTS

主要用語と概念

how exons mix to form new genes

Exon recombination helps new genes form by mixing exons from the same gene or from different genes. This process is also called exon shuffling or domain shuffling. It has been seen in vertebrates, invertebrates, and some plants, including potatoes and sunflowers.

During exon recombination, exons join in new exon-intron combinations. These new combinations may later become new genes. Exon shuffling follows splice frame rules, which means the exons must fit the reading frame correctly.

Each exon has three reading frames. Incoming exons can join in any one of the three frames, and that can cause a frameshift mutation. Because of this, not every recombination event is helpful. Some events can create a premature stop codon and a protein that is not fully made.

In human evolution, exon shuffling has helped shape several human-specific genes. It worked alongside gene duplication and divergence. One example is the MCH gene, which underwent exon recombination by retrotransposition about 25 million years ago in early primates.

That event created new intron-exon boundaries, which later evolved into the Hominidae-specific conserved gene PMCHL1. PMCHL1 is a pseudogene, but its antisense RNA is expressed in the human brain. Because the original MCH gene encoded a neuropeptide involved in energy balance and body weight in rodents, PMCHL-1 is expected to have similar functions.

Illegitimate recombination is one of the most common ways exon recombination happens. It can duplicate exons and has been seen in several human diseases, including Duchenne and Becker muscular dystrophy, familial hypercholesterolemia, Lesch-Nyhan syndrome, hemophilia, and lipoprotein lipase deficiency.

How Exons Mix to Form New Genes

evolutionary relationships through genome comparisons

evolutionary-relationships-through-genome-comparisons

Tracing Evolution with Genome Data

Genome data helps scientists trace how organisms are related over time. When two species share a common feature, it is often encoded by DNA sequences that have stayed conserved in both species. As genome sequencing improved in the late 20th century, researchers gained a better way to compare conserved domains across species and use that evidence to infer evolutionary relationships. Genome comparison can show evolutionary relationships at three levels. At the broadest level, it highlights...

genome copying errors

DNA Replication Error Checks

DNA replication includes built-in error checks that protect the genome during cell division. Even though this process copies millions of base pairs with high fidelity, a wrong base or a longer stretch of wrong bases can still be added to the daughter strands. If these mistakes are not corrected, cells may build up mutations that can threaten survival. One level of repair is proofreading. DNA polymerase enzymes, which build the new DNA strand, can make about 1 incorrect nucleotide per 100,000...

phylogenetic trees

Reading Evolution in Phylogenetic Trees

Phylogenetic trees show how organisms are related through evolution. They map branching patterns that trace common ancestry and help scientists compare species over time. A phylogenetic tree can be read like a family tree for life. Each branch point marks a split from a shared ancestor, and the pattern of branches shows how closely related different organisms are. These trees are used to organize biological information and to study evolutionary change. They can also help scientists understand...

synteny and evolution

Chromosome Rearrangements and Synteny

Chromosome rearrangements and synteny show how shared gene order can reveal evolutionary history. Synteny means genes are found on the same chromosome, even if they are not genetically linked. John H. Renwick coined the term in 1971. Species with common ancestry often keep conserved syntenic regions. Scientists use synteny to compare the evolutionary relationship between species. Human and mouse lineages split from a common ancestor about 80 million years ago. Since then, the ancestral...

multi-species conserved sequences

Conserved DNA Across Species

Conserved DNA across species shows how some genome regions stay nearly unchanged over time. Next-generation sequencing has built large genome databases for many animals and plants. Since the Human Genome Project, scientists have compared the genomes of primates, mammals, and other distant species. These large studies have helped reveal evolutionary relationships between organisms. Although species genomes differ greatly, a few DNA sequences are highly conserved. Conserved DNA sequences found...

gene duplication and divergence

How Duplicate Genes Shape Evolution

Gene duplication helps drive evolution by creating extra copies of DNA that can change over time. The seminal work of Ohno in 1970 helped popularize this idea. DNA sequence comparisons show that many genes in bacteria, archaebacteria, and eukaryotes came from duplication and later divergence, which makes this process important in evolution. The duplicated copies of a gene are called paralogs. When paralogs have similar sequences and functions, they form a gene family. Many gene families have...

exon recombination

Exon recombination helps new genes form by mixing exons from the same gene or from different genes. This process is also called exon shuffling or domain shuffling. It has been seen in vertebrates, invertebrates, and some plants, including potatoes and sunflowers. During exon recombination, exons join in new exon-intron combinations. These new combinations may later become new genes. Exon shuffling follows splice frame rules, which means the exons must fit the reading frame correctly. Each...

comparing copy number variations and snps

comparing-copy-number-variations-and-snps

Genome Variation in CNVs and SNPs

Genome variation in CNVs and SNPs shows how DNA can differ across people in a population. These differences may involve a single nucleotide, which is one DNA base, or a larger chromosomal change. Scientists study them to understand inherited variation in the human genome. Copy number variations, or CNVs, are structural changes that cover more than 1 kb of DNA sequence. A CNV can change the number of copies of a gene or a group of genes. The main forms are deletion, tandem duplication,...

key terms and concepts

Exon recombination, or exon shuffling, can create new gene combinations. Learn how reading frames, frameshifts, and human gene examples fit this process.

How Exons Mix to Form New Genes | JoVE K12

molecular biology

JoVE Core 分子生物学は、明確で簡潔なアニメーション ビデオ レッスンを通じて細胞の分子プロセスを紹介します。さらに、科学者の実際のビデオでは、これらの概念の応用が現代の研究室での実際の実験を通じて実証されています。

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Biology

Evolution

Speciation

Tennessee Academic Standards

Heredity

BIO1.LS3.2

Virginia  Standards of Learning

HIgh School

BIO.5

BIO.5.d

Minnesota Academic Standards in Science

Life Science

3.2.1 9L.3.2.1.3

new-jersey-student-learning-standards-for-science

New Jersey Student Learning Standards for Science

Biological Evolution: Unity and Diversity

Arizona Science Standards

HS+B.L3

HS+B.L3U1.12

HS+B.L4

HS+B.L4U1.13

Alabama Course of Study Science

Unity and Diversity

9-12.B.4.13

The DNA Helix

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Genome Copying Errors

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Phylogenetic Trees

Gene Duplication and Divergence

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Comparing Copy Number Variations and SNPs

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Natural Selection

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Artificial Selection

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Gene Flow

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This ...

Construct an explanation based on evidence that biological diversity is influenced by (1) the potential for a species to increase in number, (2) the heritable genetic variation of individuals in a species due to mutation and sexual reproduction, (3) competition for limited resources, and (4) the proliferation of those organisms that are better able to survive and reproduce in the environment. Emphasis is on using evidence to explain the influence each of the four factors has on number of organisms, behaviors, morphology, or physiology in terms of ability to compete for limited resources and subsequent survival of individuals and adaptation of species. Examples of evidence could include mathematical models such as simple distribution graphs or proportional reasoning.

HS-LS4-2

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Hardy-Weinberg Principle

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Apply concepts of statistics and probability to support explanations that populations of organisms adapt when an advantageous heritable trait increases in proportion to organisms lacking this trait. Emphasis is on analyzing shifts in numerical distribution of traits and using these shifts as evidence to support explanations for adaptations. Explanations could include basic statistical or graphical analysis.

HS-LS4-3

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Formation of Species

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Speciation Rates

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Genetics of Speciation

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Hybrid Zones

Hybrid zones are narrow regions where two closely related species interact, mate, and produce hybrids. Relative to either parent species, hybrids may ...

Extinction

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Evaluate evidence supporting claims that changes in environmental conditions can affect the distribution of traits in a population causing: (1) increases in the number of individuals of some species, (2) the emergence of new species over time, and (3) the extinction of other species. Emphasis is on determining cause and effect relationships for how changes to the environment such as deforestation, overfishing, application of fertilizers, drought, flood, and the rate of change of the environment affect distribution or disappearance of traits in species.

HS-LS4-5

How Exons Mix to Form New Genes

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