Duke Research Blog

Following the people and events that make up the research community at Duke.

Author: Anne Littlewood

Sean Carroll on the Evolution of Snake Venom

What’s in a snake bite?

According to University of Wisconsin-Madison evolutionary biologist Sean Carroll who visited Duke and Durham last week, a snake bite contains a full index of clues.

In his recent research, Carroll has been studying the adaptations of novelties in animal form, such as snake venom. Rattlesnakes, he explains, are the picture of novelty. With traits such as a limbless body, fangs, infrared pits, patterned skin, venom, and the iconic rattle, they represent an amazing incarnation of evolution at work.

Rattlesnakes: the picture of novelty (Photo from USGS)

Snake venoms contain a complex mixture of proteins. This mixture can differ in several ways, but the most interesting difference to Carroll is the presence or absence of neurotoxins. Neurotoxic venom has proven to be a very useful trait, because neurotoxins destroy the nervous tissue of prey, effectively paralyzing the animal’s respiratory system.

Some of today’s rattlesnake species have neurotoxic venom, but some don’t. So how did this happen? That’s what Carroll was wondering too.

Some genes within genomes, such as HOX genes, evolve very slowly from their original position among the chromosomes, and see very few changes in the sequence in millions of years.

But snake venom Pla2 genes are quite the opposite. In recent history, there has been a massive expansion of these genes in the snake genome, Carroll said. When animals evolve new functions or forms, the question always arises: are these changes the result of brand new genes or old genes taking on new functions?

Another important consideration is the concept of regulatory versus structural genes. Regulatory genes control the activity of other genes, such as structural genes, and because of this, duplicates of regulatory genes are generally not going to be a favorable adaptation. In contrast, structural gene activity doesn’t affect other genes, and duplicates are often a positive change. This means it is easier for a new structural gene to evolve than a regulatory one. Carroll explained.

Evolutionary Biologist Sean Carroll (Photo from seanbcarroll.com)

Carroll examined neurotoxic and non-neurotoxic snakes living in overlapping environments. His research showed that the most recent common ancestor of these species was a snake with neurotoxic venom. When comparing the genetic code of neurotoxic snakes to non-neurotoxic ones, he found that the two differed by the presence or absence of 16 genes in the metalloproteinase gene complex. He said this meant that non-neurotoxic venom could not evolve from neurotoxic venom.

So what is the mechanism behind this change? What could be the evolutionary explanation?

When Carroll’s lab compared another pair of neurotoxic and non-neurotoxic species in a different region of the US, they found that the two species differed in exactly the same way, with the same set of genes deleted as had been observed in the first discovery. With this new information, Carroll realized that the differences must have occurred through the mechanism of hybridization, or the interbreeding of neurotoxic and non-neurotoxic species.

Carroll’s lab is now doing the structural work to study if the genes that result in neurotoxic and  non-neurotoxic protein complexes are old genes carrying out new functions or entirely new genes. They are using venom gland organoids to look into the regulatory processes of these genes.

In addition to his research studying the evolution of novelties, Carroll teaches molecular biology and genetics at Madison and has devoted a large portion of his career to  storytelling and science education.

Meet New Blogger Anne Littlewood – Working on Biology and Puppies

My name is Anne Littlewood and I am a sophomore here at Duke. I grew up in San Francisco, spent a brief moment living on the island of Kauai, and finished high school in Pebble Beach, California. I am studying the intersection of biology and psychology here at Duke, in an effort to understand how biological mechanisms inform our interactions with the environment.

Snuggles in Puppy Kindergarten!

Outside the classroom, I can be found frequenting Duke’s beloved Puppy Kindergarten, where I work as a volunteer. Recently, I’ve become an Associate Editor for Duke’s literary magazine, The Archive. I love writing creatively, and it’s been so great to find a community of my literature- loving peers. I’m also participating in a Bass Connections project this year, and working on a team to evaluate the outcomes of different conservation interventions through the synthesis of an evidence gap map for World Wildlife fund.

Me and Cricket on Carmel Beach

Most of all I love to spend time outdoors, whether it’s exploring the mountains of North Carolina on a backpacking trip, lying in my hammock at Eno Quarry, or walking through the gardens each day on my way to class. I’m a huge animal lover, and I’m way too obsessed with my dog, a 12-pound cavalier King Charles spaniel named Cricket.

I’ve always been into science, but I think I really fell in love with Biology my freshman year of high school, when my all time favorite teacher, Mr. Cinti helped me extract my DNA one afternoon, just for fun. Writing is my passion, and I’m excited to explore my skills in a variety of genres this year. This blog is my first ever attempt at journalism/ science writing, and I’m excited to give it a try!

Creating a Gender Inclusive Campus: Reflecting on “Becoming Johanna”

Following Duke’s Oct. 4 screening of the 2016 documentary, “Becoming Johanna,” students, faculty, staff and community members in the audience were eager to ask questions of the panel, which included the film’s director/producer, Jonathan Skurnik, and even the film’s transgender subject, Johanna Clearwater herself.

Johanna Clearwater pictured with the film’s director/producer Jonathan Skurnik

The film showcases the heart-wrenching and empowering story of a latina transgender teenager growing up in Los Angeles. After beginning her transition at age 16, Johanna faced the rejection of her mother and intense opposition from school authorities. Soon after, she was abandoned by her family and entered the foster care system, where she was lucky to find a much more supportive family environment. After changing schools, she connected on a personal level with her school principal, Deb, who helped Johanna find a community where she felt understood and supported. This success story of self-advocacy and resilience in the face of abandonment and exclusion highlights the daily struggles of many transgender teenagers. For these individuals, becoming comfortable in their own skin is the end of a long and demanding journey, often made even more difficult by the ignorance and cruelty of society. Finding and following the path to authentic expression takes a huge amount of courage, as this route is often layered with adversity.

Before the screening, Duke clinical social worker Kristin Russel put the film in context for the audience, inviting our reflection with her words: “A well told story… is really what can help us bridge the unfortunate distance that can remain uncrossed and misunderstood if such stories are silenced.” Chief Diversity Officer for the School of Medicine Judy Seidenstein then introduced the film and facilitated the panel discussion.

After the film, the audience was invited to join the conversation. Questions came from every demographic of the crowd, and provided a nice sampling of opinions. Many audience members pointed out how important these conversations are, especially in a conservative state like North Carolina that has so recently struggled with the protection of LGBTQ rights with last year’s ‘Bathroom Bill.’ Specifically, the questions and comments from hospital staff and faculty from the School of Medicine gave a nice insight into the direction of support on campus for sexual and gender diversity.

Audience members reflect on the film with those nearby

Cheryl Brewer, the Associate Vice President of Nursing, told the room about the inclusion work that she is leading in the School of Nursing. They have developed a new core curriculum to promote acceptance and support of gender and sexual diversity through situational trainings. She noted that there have been some people that struggle with implicit biases more than others, but that the program has been a success overall.

Russell spoke briefly about her work with transgender and gender diverse youth in the clinical setting and emphasized the importance of having family support. Legally and psychologically, maintaining family involvement and support of patients is essential for treatment.

Events like this one reflect ongoing efforts to support sexual and gender diversity within and beyond Duke, by promoting conversation and increasing empathy through storytelling. Duke is well on the way to becoming a much more inclusive community, where everyone can feel a sense of belonging.

Guest post by Anne Littlewood

Page 2 of 2

Powered by WordPress & Theme by Anders Norén