A new study led by an Iowa State University evolutionary biologist links primary cilia—antenna-like cell protrusions widely studied in human health—to how turtle embryos detect sex-deciding nest temperatures. Following research across painted and spiny softshell turtles, the findings open a new avenue bridging basic evolutionary science and biomedical research.
When most baby turtles hatch, the temperature of the sand or soil where their mother laid the eggs determines whether they become male or female. Warm incubation typically produces females, while cooler nests produce males. Now, a new study led by an Iowa State University evolutionary biologist suggests a once-ignored cell component called primary cilia may help turtle embryos detect that sex-deciding warmth.
Cellular Sensors and Turtle Sex Determination at Iowa State University
Primary cilia are antenna-like protrusions extending from most types of animal cells. While they have become a growing focus of human health research due to their recognized importance in development and disease, they have never before been linked to turtle sex determination. That connection has drawn interest from Nicole Valenzuela’s research team at Iowa State University.
“We have concluded we need to open a whole new research avenue to characterize primary cilia in turtles and see how they’re composed, what they are doing, and how they are changing and responding to temperature and other cell signals.”
Nicole Valenzuela, professor of ecology, evolution and organismal biology at Iowa State University
Valenzuela studies how evolution and environmental factors influence complex traits such as sex determination. Over an evolutionary lineage spanning more than 200 million years, some turtle species have developed sex-specific chromosomes that dictate whether an individual becomes male or female. However, most species remain temperature-dependent.
Comparing Painted Turtles and Spiny Softshells to Model Regulatory Networks
To understand the genetic basis behind these divergent reproductive strategies, the research team examined the genes involved in making reproductive organs across two specific species. They analyzed painted turtles, which have retained the ancestral temperature-driven method, and spiny softshell turtles, which utilize sex chromosomes.
Researchers integrated data on gene expression, protein-protein interactions, and protein-DNA interactions to model molecular regulatory networks for sex-development genes. This approach captured a snapshot of cellular control circuitry as gonads emerged during embryonic development.
A comparison of these regulatory networks showed that painted and spiny softshell turtles share 89 transcription factor hubs—specialized proteins responsible for turning clusters of genes on and off. Fifty of those 89 hubs remained unchanged between the two species, potentially representing the core mechanism for building turtle gonads.
However, when researchers examined the hubs that underwent the most change and cross-referenced them against databases tracking known gene functions, a term appeared that they did not anticipate: primary cilia.
Broader Scientific Implications for Biology and Human Health Research
Other scientists in the field shared that initial surprise. When Valenzuela presented the findings at the International Symposium on the Biology of Vertebrate Sex Determination, she asked a roomful of colleagues how many had heard of primary cilia. Only a couple of hands went up.
Despite its unexpected nature, the relationship between primary cilia and sex differentiation in turtles appears robust. Multiple analytical approaches linked transcription factor hubs to primary cilia, with specific gene targets shifting from antenna function in painted turtles to structure and formation in spiny softshells. A forthcoming study from the lab examining turtle embryo histones—proteins that provide spools for DNA to wind around—uncovered related associations.
Primary cilia are known to detect environmental cues outside of cells, including temperature fluctuations, and manage major signaling pathways linked to mammalian sexual development. While further investigation is required to validate the hypothesis that the cellular antenna plays a direct role in determining turtle sex, insights gained from the research could inform broader biomedical inquiries.
Dysfunctional cilia have already been implicated in an expanding roster of human disorders, including cancer as well as brain and lung diseases.