Organs take sides

 作者:唐泣     |      日期:2019-03-08 07:02:00
By Jon Copley A SINGLE gene may choreograph the positions of our organs by directing cell division, say researchers in Germany. In vertebrates, organs inside the chest and abdomen are arranged asymmetrically. The apex of the heart points towards the left, for instance, while the large intestine curls from right to left. Biologists have found several signal molecules that seem to determine the right and left sides at very early embryonic stages (This Week, 25 April 1998, p 15). But how they do this is not clear. “They are gone long before the organs develop,” says Martin Blum of the Karlsruhe Research Centre. But Blum and his colleagues have discovered a clue to what happens. They found that a gene called Pitx2 was switched on in cells destined to become the left sides of the heart and gut in developing embryos of mice, frogs and zebra fish. The gene stayed switched on as these organs developed. The team also tested the effects of Pitx2 on the right-hand sides of frog embryos by injecting messenger RNA corresponding to the gene. Some of these embryos developed mirror images of normal organ arrangements, while others developed extra-large hearts and guts (Development, vol 126, p 1225). “Basically, Pitx2 could serve as a mediator between the signal molecules and the forming organs,” says Blum. The signal molecules may switch on Pitx2 before disappearing, leaving the gene to carry out their instructions as organs develop. Blum thinks the gene works by controlling cell proliferation. If more cells grow on one side of the gut than the other, for example,