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Xu receives prestigious early career award for evolutionary biology research

William “Bill” Ross Meacham, January 12, 1923-September 22, 2020
Sen Xu, UTA assistant professor of biology

An evolutionary biologist at The University of Texas at Arlington has been recognized for his outstanding research with a prestigious national award to study how genetic diversity is achieved at the molecular level.

Sen Xu, assistant professor of biology, received a National Science Foundation Faculty Early Career Development (CAREER) Program Award, which includes grants totaling $1,150,000 over a five-year period. Xu’s project title is “CAREER: Understanding the Evolution and Genetic Basis of Meiotic Recombination Rate.”

CAREER awards are given in support of early-career faculty who have the potential to serve as academic role models in research and education and to lead advances in the mission of their department or organization, according to the NSF.

“I am very grateful that NSF funds this innovative research direction,” Xu said. “Personally, it is a great honor to be recognized with this award.”

College of Science Dean Morteza Khaledi said the award is a fitting recognition of the quality of Xu’s research and its importance in his field.

“This is a tremendous achievement for Dr. Xu and shows again the high level of research and teaching being done in the College of Science,” Khaledi said. “Dr. Xu’s work has the potential to make significant advances in our knowledge of evolutionary processes and how they affect genetic diversity.”

In his research, Xu examines how the process of recombination in sexual organisms is modified by genetic variants and through interaction with environmental changes.

Recombination is a process in which parts of DNA are broken and recombined to produce new combinations of alleles, or specific forms of genes. This process creates genetic diversity at the level of genes that reflects differences in the DNA sequences of different organisms.

Recombination is a fundamental part of meiosis, a special type of cell division that gives rise to sperm and eggs. Recombination is essential for safeguarding the integrity of genomes of sperm and eggs, Xu said.

Xu’s CAREER project will address an important yet understudied question in evolutionary biology – whether recombination rates evolve in response to natural selection in animals and plants, and what genes control the variation of recombination rates.

“What recombination does is to shuffle the DNA sequences of a pair of chromosomes, for example, between our two copies of chromosome 1,” Xu said. “We humans inherit half of our genomes from our father and half from our mother. Interestingly, what we inherit from our parents is a shuffled combination of genes from our grandfather and grandmother, thanks to recombination that happens in meiosis. It is also interesting to note that recombination rate varies extensively between individuals, populations, and species.”

Despite recombination being such an important process, relatively little is known about what evolutionary processes govern the evolution of recombination rates, Xu noted.

“This stems from the current limitation of how we estimate recombination rates,” he said. “Estimating the recombination rate through constructing a genetic map for a species is tedious and labor expensive, often requiring us to sample hundreds of individuals in a crossing experiment and collect information on hundreds of molecular markers. All these efforts in the end would give us one genetic/recombination map. That is why for most species we study in biology, we have at most a handful of genetic maps.”

To overcome the limitation of how recombination is estimated, Xu’s project will develop a novel approach of whole-genome sequencing single sperms. Building on his previous work, this approach will allow Xu and his research group to sequence the entire genome of hundreds of sperm with thousands of molecular markers in a rapid and economical way, he said.

Xu and his team will use this approach with their chosen model organism, the microcrustacean Daphnia, or water flea, which lives in freshwater habitats around the world.

“Hopefully, the development of this approach will stimulate researchers working on other species to use this technology for studying recombination rate as well,” Xu said.

The funded research project will also take advantage of this single sperm sequencing approach to estimate the recombination rate for multiple populations in two Daphnia species.

“In each population, we will build genetic maps for multiple individuals, which would yield hundreds of genetic maps for each species,” he said. “This large number of genetic maps will then empower us to understand whether the divergence of recombination rates between populations and between species is driven by natural selection.”

Lastly, with these recombination rate estimates from hundreds of Daphnia individuals, Xu will perform genome-wide association analyses to pinpoint the genes and genetic variants that contribute to the variation of recombination rate among individuals, populations, and species. Once identified, he and his team will use a gene editing technique called the Crispr-Cas9 approach to introduce these genetic variants to a common genetic background to test their effects on recombination rates in Daphnia.

In 2019, Xu was awarded a five-year, $1.89 million grant from the National Institutes of Health for a study which also utilizes Daphnia, in this case to investigate fundamental biological processes that can lead to fertility problems in humans.

Xu received a B.S. in Biological Sciences from Ocean University of China in Qingdao, China, in 2003; an M.S. in Biological Sciences from the University of Amsterdam in 2005; and a Ph.D. in Environmental Science from the University of Windsor in Ontario, Canada, in 2011. He served postdoctoral fellowships at Indiana University from 2012-15 and at Great Lakes Institute for Environment Research, University of Windsor, in 2015-16. He came to UTA in fall 2016.

Xu is the third College of Science faculty member to receive a national early career award in the past four years. He Dong, associate professor of chemistry and biochemistry, received an NSF CAREER award in 2018, and Matt Walsh, associate professor of biology, received an NSF Presidential Early Career Award for Scientists and Engineers (PECASE) in 2019.