Wallabies' 'Jumping Genes' Key
Rock wallabies are dog-sized marsupials - small kangaroos - that live around rock outcrops in Australia. They are of intense interest to Rachel O'Neill, assistant professor of molecular and cell biology, who wants to know why so many species of this rarely seen animal have developed in close quarters, and how new species are formed.
But she's not interested in the big picture on rock wallabies - their big feet, their four-meter leaps, their long tails. She looks at the marsupials from a much smaller perspective, examining their chromosomes under a microscope to learn how hybrid rock wallabies may change the genome.
Rock wallabies are ideal candidates for her interest. They have few, large chromosomes, they hybridize readily, and they show extraordinary chromosome diversity in a short period of time.
From studying rock wallabies, O'Neill has suggested that new species can form very rapidly - much more rapidly than evolution is expected to occur - when 'jumping genes,' mobile segments of DNA that act like wild cards, are expressed in a hybrid. In most animals, defense mechanisms stop this expression: in biologists' terms, the jumping genes are silenced.
But in the rock wallaby hybrids she has studied, the "jumping genes" insert themselves into chromosomes at fertilization and repeat themselves thousands of times, scrambling the chromosome arrangement.
If that new arrangement is reproduced in offspring of the hybrid, which can happen fairly rapidly among rock wallabies, and the offspring thrive, a new species may form.
O'Neill proposed this in what New Scientist magazine called a "landmark paper" in Nature in 1998, just before she came to UConn. Since joining the UConn faculty in 1999, she has won a prestigious National Science Foundation (NSF) Career grant that is enabling her to continue her research into why the wallaby hybrids are jumping - not physically, but in their chromosome arrangements.
Jumping genes are massed in the centromere, the 'X' at the center of every chromosome. O'Neill called them the 'black hole' of genetics - they don't code for genes, they can't be sequenced, and not much is known about them. She is proposing that they may have a role in the formation of species.
O'Neill's research adviser at La Trobe University in Australia, Jennifer Marshall Graves, a collaborator on the Nature paper, has likened the speed of the change found in the wallaby genome to five minutes instead of 50 million years. The third collaborator on the paper was Michael O'Neill, assistant professor of molecular and cell biology at UConn, Rachel's husband, and a specialist in genetic imprinting, or gene expression that depends on the sex of the parent that transmitted it.
Rachel O'Neill first encountered rock wallabies when she began working on her doctorate at La Trobe with Graves, who was known for her gene mapping work and was the premier researcher in Australia on rock wallabies. Rachel had earned her bachelor's degree in zoology at the University of Texas, where Michael earned his Ph.D. When he went to Melbourne to take a postdoctoral position, she went too and began graduate studies.
"I was always a science nerd," she says, recalling how she watched Nova and played with a chemistry set as a child.
The rock wallabies have proved particularly fascinating to her. She takes "ear punches" from them - a sample of tissue that she says is like piercing an ear - and studies their chromosomes, stained purple, green, and red, under a microscope. "My work is very visual," she says.
Rock wallabies are hard to catch, so the samples often come from wallabies living in a fauna park.
"They love peanut butter," she says. Lured with it, they are caught and put in a potato sack, which makes them sleepy. "They think they're back in the pouch," she explains. Her biggest challenge with the samples, now that her lab is at UConn, is getting them out of Australia, which requires a variety of permits, as well as getting them through airport security without opening, and destroying, the cultures.
Besides working on the rock wallaby genome, O'Neill studies mice (it's easier to obtain samples, she notes) and, in collaboration with her husband, fish from the Poeciliopsis, or desert top minnow, colony at UConn.
Her $645,000 NSF Career grant, now in its third year, includes a teaching component that helps graduate students travel to Australia to study and gather samples. She also teaches students the latest technical advances in genomics and is developing new curricula for high school, college, and graduate students. Her research group includes four Ph.D. students, two undergraduates, and master's degree and postdoctoral researchers. She and Michael hold joint meetings of their research groups, and they both host high school students for three weeks in the summer as part of the UConn Mentor Connection.
She plans to continue her marsupial research, partly because it is so unusual. Marsupials are considered a "non-model" system by NSF - few researchers work on them - so she has to develop her own resources to understand the marsupial genome, such as developing her own cell lines.
But it also means that everything she learns about the marsupial genome "is new and novel and exciting," she says. "Every question we answer raises six or more questions. We are developing resources for other scientists."