Two geneticists have identified a link between the human heart and a group of contracting cells in Hydra, a simple creature that may resemble some of the earliest multicellular animals. The water-dwelling Hydra is basically a quarter-inch tube topped with a set of tentacles for dragging food into one end. The area around
Courtesy of Hiroshi Shimizu and Toshitaka Fujisawa
the other, sealed end of the tube, called the peduncle, can contract in a pumping motion that helps mix nutrients. Hiroshi Shimizu and Toshitaka Fujisawa of Japan’s National Institute of Genetics propose that the heart may have evolved from the peduncle of Hydra
or a similar creature.
Shimizu and Fujisawa injected calligraphy ink into the peduncle and noted that the pumping action there is suggestive of the beating of a heart. Several clues indicate this similarity is no coincidence. Hydra has a gene that instructs nerve cells to produce a molecule that powers the peduncle’s contractions. Higher organisms possess a related gene that similarly revs up the heart. Another gene active in the peduncle is related to one that, in higher organisms, functions prominently in embryonic heart tissue. This finding fits with evidence that embryos at times pass through stages resembling their species’ ancestors, the researchers note.
The peduncle was apparently “refined during evolution and relocated more to the middle of the body,” says Hans Meinhardt, a theoretical biologist at the Max Planck Institute for Developmental Biology in Tübingen, Germany. Even in humans, heart tissue originates at the tip of the embryo, where Hydra’s peduncle would be. Anatomic and genetic evidence suggest another surprise, he adds: Hydra’s mouth corresponds to our rear end.