Science Focus (issue 26)

By Sonia Choy 蔡蒨珩 Lazarus Rising: The Attempted Resurrection of the Gastric Brooding Frog The arrival of Dolly, the first cloned mammal in 1996, marked an important page in human history. It was the first time humans were able to create a mammal in a laboratory. Pictures of Dolly made headlines across the world. But did you know that scientists also tried to use the same technology to bring extinct frogs back to life? The southern and northern gastric brooding frogs (Rheobatrachus silus and Rheobatrachus vitellinus) were discovered in 1972 and 1984 in Queensland, Australia respectively. Both being very small (about 30– 54 mm for the southern and 55–80 mm for the northern species) and living in a limited rainforest area (less than 1000 km2), they lived in streams of the Queensland mountain ranges [1, 2]. Like many native Australian species, the frogs were unique to the land down under, and possessed extremely unique characteristics. One such thing that caught headlines at that time was how they reproduce [3]. The mother swallows a number of eggs and stops producing acid in its stomach to allow the eggs to hatch into tadpoles, and later into frogs. It was suggested that a substance called prostaglandin E2 secreted by the tadpoles can inhibit the acid secretion of the mother [4]. Then the mother does not eat for six weeks and stops breathing through the lungs but the skin, as its bloated stomach has squeezed the lungs to collapse. Eventually, the mother gives birth to fully formed baby frogs via “propulsive vomiting”, much like a Russian doll. This dramatic method caught the attention of many, including zoologists who couldn’t believe this was true…until they saw it for themselves. Sadly, these frogs did not live very long, and by 1981, the southern breed had gone extinct in the wild; the northern breed was also extinct in 1985, within a year after its discovery. Mike Archer, a researcher from the University of New South Wales, had read about the frog and decided to 拉撒路復活: 絕種胃育蛙重生記 do something no one had seriously attempted before – to bring it back to life [3]. His plan was to use somatic cell nuclear transfer (SCNT) to transfer a somatic cell nucleus obtained from the frozen frog sample to a fresh egg of a reasonably close but existing relative, the barred frog (Mixophyes fasciolatus). With a full set of the southern gastric brooding frog’s DNA as the blueprint of life, they hoped the cell can divide and develop into a fullfledged individual. SCNT is divided into a few main steps. The first step was to use ultraviolet radiation to destroy the nuclear DNA of a donor egg [5]. Into this “empty” egg, scientists inserted a nucleus collected from the long frozen gastric brooding frog’s tissue sample. For the cell to divide and grow into an embryo, an electrical or chemical stimulation is usually given to activate the manipulated oocyte [6]. After many cell divisions, the embryo then underwent the crucial step of development, known as gastrulation, when cells in its exterior migrate internally – and there it stopped [3]. In the best-case scenario, the cell division and differentiation would continue further, to the point that we have a fully formed tadpole of the southern gastric brooding frog. Current technology is very far from even creating a southern gastric brooding frog tadpole, but Mike Archer’s great dream is to bring the frog back to life. This is partially for the potential medical benefits it may bring. As mentioned earlier in the article, female frogs temporarily stop the production of gastric acid after they swallow the egg and let it hatch. However, the species was extinct before scientists could further study them [7, 8]. If the cloning process is successful, this would lead to a better understanding of the southern gastric brooding frogs, and potentially help human patients suffering from too much or unwanted gastric acid. From acid reflux to ulcers and even more serious diseases, this