Sharks#39; Sixth Sense Related to Human Genes

摘要：The same genes that give sharks their sixth sense and allow them to detect electrical signals are also responsible for the development of head and facial features in humans, a new study suggests. 美國科學家的一項最新研究顯示，使鯊魚具有第六感并讓它們能夠檢測電流信號的基因?qū)θ祟愵^部和面部特征的發(fā)育也起著重要作用。

The same genes that give sharks their sixth sense and allow them to detect electrical signals are also responsible for the development of head and facial features in humans, a new study suggests.

The finding supports the idea that the early sea creatures which eventually evolved into humans could also sense electricity before they emerged onto land.

The study, led by Martin Cohn and his lab at the University of Florida, is detailed in the current issue of the journal Evolution & Development.

Sharks have a network of special cells that can detect electricity, called electroreceptors, in their heads. They use them for hunting and navigation.

This sense is so developed that sharks can find fish hiding under sand by honing in on the weak electrical signals emitted by their twitching muscles.

The researchers examined embryos of the lesser spotted catshark. Using molecular tests, they found two independent genetic markers of neural crest cells in the sharks#39; electroreceptors.

Neural crest cells are embryonic cells that pinch off early in development to form a variety of structures. In humans, these cells contribute to the formation of facial bones and teeth, among other things.

The finding suggests that neural crest cells migrate from the sharks#39; brains to various regions of the head, where they develop into electroreceptors.

Glenn Northcutt, a neuroscientist at the University of California, San Diego, who was not involved in the study, said the finding was interesting, but that more studies are needed before a direct link between neural crest cells and electroreceptors can be established.

"It still requires a definitive experiment, where the developing neural crest cells are marked with dye, the embryo develops and the dye clearly shows up in the electroreceptors," Northcutt said.

In the new study, the researchers found snippets of genetic material associated with neural crest cells in the electroreceptors. They did not dye the neural crest cells and trace their development.

Scientists think that all primitive animals with backbones, including the early ancestors of humans, could sense electricity. As they evolved, mammals, reptiles, birds and most fish lost the ability. Today, only sharks and a few other marine species, such as sturgeons and lampreys, can sense electricity.

"Our fishy ancestors had the anatomy for it," said study team member James Albert, a biologist from the University of Louisiana.

The ability to sense electrical signals is useful in aquatic environments because water is so conductive. On land, however, the sense is useless.

"Air doesn#39;t conduct electricity as well," Albert said. "When it happens, it#39;s called a lightning bolt and you don#39;t need special receptors to sense it."

The development of the electroreceptors is believed to mirror the development of the lateral line, a sense organ in fish that allows them to detect motion in surrounding water. Similar processes are thought also to be involved in the development of the inner ear, the organs which help humans keep their balance.

The electroceptors are also believed to behind many sharks#39; ability to detect changes in the Earth#39;s magnetic field. Other studies indicate that like sailors, sharks can also navigate by celestial cues.

美國科學家的一項最新研究顯示，使鯊魚具有第六感并讓它們能夠檢測電流信號的基因?qū)θ祟愵^部和面部特征的發(fā)育也起著重要作用。

據(jù)“生活科學”2月7日報道，這一發(fā)現(xiàn)支持了此前的一個觀點，即最終進化為人類的早期海洋生物在它們尚未開始陸地生活之前，也能夠探測到水中的電流信號。

鯊魚頭部有個能探測到電流的特殊細胞網(wǎng)狀系統(tǒng)，被稱為電感受器。鯊魚就利用電感受器來捕食獵物及在水中自由游弋。美國研究人員對小斑點貓鯊的胚胎進行了研究。通過分子測試，他們在鯊魚的電感受器中發(fā)現(xiàn)了神經(jīng)嵴細胞的兩種獨立基因標志。神經(jīng)嵴細胞是胚胎發(fā)育早期形成各種組織的胚胎細胞。人類的神經(jīng)嵴細胞對人面部骨骼和牙齒的形成起重要作用。這一發(fā)現(xiàn)說明，神經(jīng)嵴細胞從鯊魚的腦部移至其頭部的各個區(qū)域，并在其頭部發(fā)育為電感受器。

美國其他一些研究者認為這個發(fā)現(xiàn)非常有意思，但是要想在鯊魚神經(jīng)嵴細胞與電感受器之間建立直接聯(lián)系，還需要進行更多的研究。這項研究是由美國佛羅里達大學的馬丁·科恩和其實驗室負責完成的，具體研究結(jié)果被發(fā)表在日前出版的《進化與發(fā)展》雜志上。

科學家認為所有的原始脊椎動物，包括人類早期祖先在內(nèi)都具有電流感受能力。但隨著它們的進化，哺乳動物、爬行動物、鳥類和大部分魚類都喪失了這種能力�，F(xiàn)在，只剩下鯊魚和其它一些海洋生物，如鱘魚和七鰓鰻等還仍舊保留著這種“超能力”。

對此，研究成員之一、路易斯安娜大學的生物學家詹姆斯·阿伯特說：“我們的魚類祖先就擁有這樣的生理結(jié)構(gòu)�！毖芯咳藛T還表示，這種可以探測電流的能力在有水的環(huán)境下具有非常重要的作用，但是在陸地上，它就不起什么作用了。