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UND biologist researches how mechanisms related to temperature, in some animals, play a role in sex determination

Posted on 3/18/2016

University of North Dakota Graduate School Program in Biology from University of North Dakota on Vimeo.

UND biologist Turk Rhen spends a lot time thinking about the differences between the sexes.

And today, he tells us his research runs hot and cold.

Rhen recently received a three-year $820,000 grant from the National Science Foundation's Division of Integrative Organismal Systems for research titled "Epigenomic Analysis of Temperature-dependent Sex Determination."

His research-in the Department of Biology within the College of Arts and Sciences-is at the leading edge in biology.

Experiments are answering key questions about the development of sex-or gender differences-in animals. His research examines how undifferentiated gonads develop into either male or female gonads-testes or ovaries.

This work also addresses ongoing questions about how climate has shaped nature.

Temperature control

Rhen says temperature-dependent sex determination was first reported nearly 50 years ago. It has since been shown that temperature determines sex in some fish and amphibians, many lizards, numerous turtles and all crocodilians.

"Yet the molecular mechanism that converts temperature into a biological signal for male versus female development remains a mystery," Rhen said.

Rhen explains the big challenge is that the temperature response is likely regulated by more than one gene.

"Nobody has found the genes that sense temperature and convert it into a signal for the embryonic gonads to develop into testes or ovaries," he said.

Turk Rhen. Photo by Jackie Lorentz. Turk Rhen. Photo by Jackie Lorentz.

Prior research in the Rhen lab, which was also funded by the NSF, identified hundreds of thermosensitive genes in developing gonads of the common snapping turtle. Some of these genes, called epigenetic regulators, are known to turn on or turn off gene expression during embryonic development in other species, Rhen explains.

"Our new research will test the hypothesis that epigenetic mechanisms regulate expression of genes required for testis or ovary development," Rhen said. "In other words, we think these genes act as switches to ‘turn on' or ‘turn off' testis genes and ovary genes."

Lovers or fighters

Rhen says it's especially encouraging to get a grant from a federal funding agency in these days of increasingly stiff competition for dwindling research dollars.

His interest in sex determination started when he was an undergraduate here at UND, working with Dr. Jeffrey Lang (Professor Emeritus). Since then he's discovered that there's a lot more to it than a simple male-female dichotomy.

Rhen's doctoral research with David Crews at the University of Texas-Austin showed that temperature during embryonic development has a permanent effect on the brain and behavior in a lizard with temperature-dependent sex determination.

"For example, males from different incubation temperatures develop alternative reproductive strategies," Rhen said.

"Males from one temperature court females more intensely than do males from another temperature. You could say they are lovers rather than fighters," said Rhen, who's become a mentor who actively trains the next generation of scientists, such as current doctoral students Katie Russart, a native of Fargo.

"Katie is looking at the impact of Atrazine exposure on the hypothalamus and pituitary gland," he added. "These neuroendocrine tissues play a central role in regulating growth and reproduction in all vertebrates, including humans.

"She's found some interesting results--Atrazine alters gene expression in the hypothalamus and pituitary gland of snapping turtles. This is an important finding because Atrazine is a widely used herbicide, but we don't know what effects it may have on humans or on wildlife."

Agricultural link?

Rhen explains that they're potentially exposed to Atrazine because it's sprayed around the same time that turtles are nesting, and it shows up in the runoff into water that the turtles live in. Scientists believe that Atrazine may be an endocrine disruptor-it can change the natural operation of the body's hormonal system. Atrazine use in North Dakota has increased with the extension of the so-called "Corn Belt" into our region.

Research provides far more than an answer to a specific problem, according to Rhen.

"My past National Science Foundation and National Institutes of Health grants have provided extended research experiences for a large number of undergraduates at UND," Rhen said. "These experiences were critical for many of my students to go on to become physicians and Ph.Ds."

Juan Miguel Pedraza
University & Public Affairs Writer

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