Male or female? Chinese scientists find gene that determines central bearded dragon’s sex

In arid parts of central Australia, temperature plays a big part in determining whether central bearded dragon embryos emerge from their eggs as male or female. While the sex of mammals and birds is determined solely by genetics, the dragons are like turtles and crocodiles in that incubation temperature plays a part in the process. If incubated at 32 degrees Celsius (89.6 degrees Fahrenheit) or higher, some male embryos will emerge as female. If the temperature is cooler, genetics will determine the sex and these males will remain males. Rising global temperatures could have profound implications for the lizards and other reptiles that rely on this system for reproduction. The switch that caused that change was a mystery until scientists in China identified it using new sequencing technology called CycloneSEQ. In an article published in the peer-reviewed journal GigaScience in August, scientists from BGI Research said they were able to sequence longer DNA fragments to produce a near-complete genome of the lizard and identify the “master sex-determining gene”. The researchers focused on the dragon because it “is a fantastic model in studying the molecular cascades of sex determination”. Central bearded dragons have a ZW sex determination system. Dragon embryos with Z and W chromosomes normally develop as females, while those with ZZ chromosomes emerge as males. However, high incubation temperatures can cause ZZ males to sex-reverse to females. “The capacity of a ZZ embryo to develop as a normal female without the help of the W chromosome suggests that sexual fate is most likely determined by a dosage-sensitive gene on the Z chromosome,” the team wrote in the paper. The team identified the “master sex-determining gene” as the Z-linked anti-Müllerian hormone (AMH), a protein-coding gene known to drive sexual differentiation. AMH regulates the regression of Müllerian ducts in male embryos. Without AMH, these ducts develop into female reproductive organs. And temperature can make all the difference. “Developing into a male is quite challenging – only at the right temperature,” said corresponding author Li Qiye, senior researcher and director of the Digital Earth Research Institute at BGI Research. “In other words, female is the default developmental pathway for this species. Only when the expression of AMH is sufficient will the pathway be pushed towards male development.” Asked about the possibility of having mostly female hatchlings under higher temperatures, Li said global warming could become a fundamental cause of reptile extinction. “This is why we are concerned about species whose sex determination is influenced by environmental temperature and want to find out the underlying mechanism.” He said knowledge about the mechanism offered insight into possible sex interventions in the future to allow ZZ embryos to develop into males even if temperatures were above 32 degrees. “Understanding the sex determination mechanism is similar to knowing a target for a disease. Researchers can then develop targeted treatments,” Li said. “Now that we know [AMH] is a critical switch, the expression of this gene could potentially be intervened to maintain the ratio of males,” he said, adding that more work was needed to make such interventions practical and cost-effective. Li said the CycloneSEQ technology helped reveal where this gene was, answering a question that researchers raised a decade ago. “In 2015, I was part of a team that sequenced the genome of the central bearded dragon. But the technology at the time was not advanced enough to help us find the answers we were looking for,” he said. “Sex chromosomes often accumulate a lot of highly similar repetitive DNA sequences, which complicates the process for scientists trying to piece the fragments together during sequencing. “Conventional methods usually generate short DNA fragments, and they may overlook some segments. “Without technology that enabled us to assemble the entire sequence accurately, we could not identify specific regions and observe what genes there were. The story could not move forward. “Now, with the new long-read technology that can produce much longer strands of DNA accurately, scientists can assemble complex genomes.” Passionate about science? Dive deeper with the Dark Matters newsletter, a weekly in-depth analysis on China’s rise in science, technology and military that goes beneath the surface. Sign up for free now.

Male or female? Chinese scientists find gene that determines central bearded dragon’s sex

.css-1c6uqr6{color:inherit;font-weight:inherit;font-size:inherit;font-family:inherit;line-height:inherit;overflow-wrap:break-word;}Researchers warn climate change could affect the future of a species heavily influenced by temperature

Researchers warn climate change could affect the future of a species heavily influenced by temperature