South American lungfish has largest genome of any animal
By Will Dunham
WASHINGTON, Aug 16 (Reuters) -The South American lungfish is an extraordinary creature - in some sense, a living fossil. Inhabiting slow-moving and stagnant waters in Brazil, Argentina, Peru, Colombia, Venezuela, French Guiana and Paraguay, it is the nearest living relative to the first land vertebrates and closely resembles its primordial ancestors dating back more than 400 million years.
This freshwater species, called Lepidosiren paradoxa, also has another distinction: the largest genome - all the genetic information of an organism - of any animal on Earth. Scientists have now sequenced its genome, finding it to be about 30 times the size of the human genetic blueprint.
The metric for genome size was the number of base pairs, the fundamental units of DNA, in an organism's cellular nuclei. If stretched out like from a ball of yarn, the length of the DNA in each cell of this lungfish would extend almost 200 feet (60 meters). The human genome would extend a mere 6-1/2 feet (2 meters).
"Our analyses revealed that the South American lungfish genome grew massively during the past 100 million years, adding the equivalent of one human genome every 10 million years," said evolutionary biologist Igor Schneider of Louisiana State University, one of the authors of the study published this week in the journal Nature.
In fact, 18 of the 19 South American lungfish chromosomes - the threadlike structures that carry an organism's genomic information - are each individually larger than the entire human genome, Schneider said.
While huge, there are plants whose genome is larger. The current record holder is a fork fern species, called Tmesipteris oblanceolata, in the French overseas territory of New Caledonia in the Pacific. Its genome is more than 50 times the human genome's size.
Until now, the largest-known animal genome was that of another lungfish, the Australian lungfish, Neoceratodus forsteri. The South American lungfish's genome was more than twice as big. The world's four other lungfish species live in Africa, also with large genomes.
Lungfish genomes are largely composed of repetitive elements - about 90% of the genome. The researchers said the massive genome expansion documented in lungfish genomes seems to be related to a reduction in these species of a mechanism that ordinarily suppresses such genomic repetition.
"Animal genome sizes vary greatly, but the significance and causes of genome size variation remain unclear. Our study advances our understanding of genome biology and structure by identifying mechanisms that control genome size while maintaining chromosome stability," Schneider said.
The South American lungfish reaches up to about 4 feet (1.25 meters) long. While other fish rely upon gills to breathe, lungfish also possess a pair of lung-like organs. It lives in oxygen-starved, swampy environs of the Amazon and Parana-Paraguay River basins, and supplements the oxygen gotten from the water by breathing in oxygen from the air.
Lungfish first appeared during the Devonian Period. It was during the Devonian that one of the most important moments in the history of life on Earth occurred - when fish possessing lungs and muscular fins evolved into the first tetrapods, the four-limbed land vertebrates that now include amphibians, reptiles, birds and mammals.
Because the forerunners of today's lungfish were ancestral to the tetrapods, their genomes can provide insight into how vertebrates long ago evolved features such as limbs that enabled life on land.
For instance, the researchers showed that the genetic machinery controlling the activity of the so-called Sonic Hedgehog Shh gene, which regulates important events during embryonic development, likely governed the formation of the bony equivalent of digits in the lungfish fin. Those digits present in the lungfish fin eventually evolved into fingers and toes in tetrapods.
"Tetrapod ancestors conquered land with limbs that evolved from fins, and were breathing air through lungs. These features probably predated the colonization of land. Only by studying the biology of the surviving lungfish lineages can we investigate the genomic basis and molecular-developmental mechanisms that facilitated the water-land transition of vertebrates," Schneider said.
Humble fern from New Caledonia boasts world's largest genome nL1N3HV2RW
Understanding of Earth's flowering plants blossoms in genome study nL2N3GW3C9
Genome study deepens mystery of what doomed Earth's last mammoths nL1N3IL04M
Genome study reveals prehistoric Ethiopian origins of coffee nL2N3GN0DF
Reporting by Will Dunham, Editing by Rosalba O'Brien
면책조항: XM Group 회사는 체결 전용 서비스와 온라인 거래 플랫폼에 대한 접근을 제공하여, 개인이 웹사이트에서 또는 웹사이트를 통해 이용 가능한 콘텐츠를 보거나 사용할 수 있도록 허용합니다. 이에 대해 변경하거나 확장할 의도는 없습니다. 이러한 접근 및 사용에는 다음 사항이 항상 적용됩니다: (i) 이용 약관, (ii) 위험 경고, (iii) 완전 면책조항. 따라서, 이러한 콘텐츠는 일반적인 정보에 불과합니다. 특히, 온라인 거래 플랫폼의 콘텐츠는 금융 시장에서의 거래에 대한 권유나 제안이 아닙니다. 금융 시장에서의 거래는 자본에 상당한 위험을 수반합니다.
온라인 거래 플랫폼에 공개된 모든 자료는 교육/정보 목적으로만 제공되며, 금융, 투자세 또는 거래 조언 및 권고, 거래 가격 기록, 금융 상품 또는 원치 않는 금융 프로모션의 거래 제안 또는 권유를 포함하지 않으며, 포함해서도 안됩니다.
이 웹사이트에 포함된 모든 의견, 뉴스, 리서치, 분석, 가격, 기타 정보 또는 제3자 사이트에 대한 링크와 같이 XM이 준비하는 콘텐츠 뿐만 아니라, 제3자 콘텐츠는 일반 시장 논평으로서 "현재" 기준으로 제공되며, 투자 조언으로 여겨지지 않습니다. 모든 콘텐츠가 투자 리서치로 해석되는 경우, 투자 리서치의 독립성을 촉진하기 위해 고안된 법적 요건에 따라 콘텐츠가 의도되지 않았으며, 준비되지 않았다는 점을 인지하고 동의해야 합니다. 따라서, 관련 법률 및 규정에 따른 마케팅 커뮤니케이션이라고 간주됩니다. 여기에서 접근할 수 있는 앞서 언급한 정보에 대한 비독립 투자 리서치 및 위험 경고 알림을 읽고, 이해하시기 바랍니다.