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Baby Turtle Turns Into a Male, Adding Fresh Dimensions to Temperature-Dependent Sex Determination Theory

Inching closer to cracking the 50-year-old puzzle of how temperature turns baby turtles male or female, researchers have uncovered a molecular link that connects temperature with sexual development. In turtles and other reptiles, whether an egg hatches male or female depends on the temperature of its nest.

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The phenomenon was first discovered in reptiles more than 50 years ago, but until now the molecular details were a mystery.
turtle, representational image, pixabay
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Inching closer to cracking the 50-year-old puzzle of how temperature turns baby turtles male or female, researchers have uncovered a molecular link that connects temperature with sexual development.

In turtles and other reptiles, whether an egg hatches male or female depends on the temperature of its nest.

The phenomenon was first discovered in reptiles more than 50 years ago, but until now the molecular details were a mystery.

In a study published in the journal Science, the researchers said they have finally identified a critical part of the biological “thermometer” that turns a developing turtle male or female.

The explanation lies not in the DNA sequence itself — the A’s, T’s, C’s and G’s — but in a molecule that affects how genes are expressed without altering the underlying genetic code, the researchers said.

"This is the first functional evidence of a molecular link that connects temperature with sexual development," Capel said.
turtle eggs, pixabay

“Temperature-dependent sex determination has been a puzzle for a really long time,” said Blanche Capel, Professor at Duke University in North Carolina, US.

“This is the first functional evidence of a molecular link that connects temperature with sexual development,” Capel said.

Unlike humans and most other mammals, the sex of many turtles, lizards, and alligators is not determined by the chromosomes they inherit, but by ambient temperatures during a sensitive stage of development.

For a common pond and pet turtle called the red-eared slider, for example, eggs incubated at 32 degrees Celsius produce all female hatchlings, while those kept at 26 degrees Celsius hatch as males.

In the study, the researchers showed that cooler egg incubation temperatures turn up a key gene called Kdm6b in the turtle’s immature sex organs, or gonads.

This, in turn, acts as a biological “on” switch, activating other genes that allow testes to develop.

Unlike humans and most other mammals, the sex of many turtles, lizards and alligators is not determined by the chromosomes they inherit, but by ambient temperatures during a sensitive stage of development.
turtles, pixabay

To home in on the critical Kdm6b gene, the researchers took a group of freshly laid turtle eggs, incubated them at either 26 or 32 degrees Celsius, and looked for differences in the way genes were turned on in the turtles’ gonads early in development — before their fate as ovaries or testes has been decided.

Further experiments showed that the protein encoded by the Kdm6b gene, in turn, interacts with a region of the genome called Dmrt1, which acts as a master switch to turn on testis development.

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“The next step is to find the temperature-sensing trigger,” said study co-author Ceri Weber, a Ph.D. candidate in the Capel lab at Duke.

“We’re trying to narrow down the possibilities,” Weber added. (IANS)

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Gene Therapy Wins Big at Portugal’s Champalimaud Foundation

The foundation, which focuses on neuroscience and oncology research at its Lisbon base, was set up at the bequest of Portugal's late industrialist Antonio Champalimaud.

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Gene Theory
ean Bennett, Albert Maguire, Robin Ali, James Bainbridge, Samuel Jacobson, T. Michael Redmond and Portugal's President Marcelo Rebelo de Sousa attend the 2018 Antonio Champalimaud Vision Awards ceremony at Champalimaud Foundation in Lisbon, Portugal, VOA

Seven scientists in the United States and Britain who have come up with a revolutionary gene therapy cure for a rare genetic form of childhood blindness won a 1 million euro ($1.15 million) prize Tuesday, Portugal’s Champalimaud Foundation said.

Established in 2006, the annual award for work related to vision is one of the world’s largest science prizes, more than the latest 9 million Swedish crown ($987,000) Nobel Prize in Physiology or Medicine.

“This is the first, and still only, example of successful gene therapy in humans that corrects an inherited genetic defect and is therefore a milestone in medical therapeutics,” said Alfred Sommer, Dean Emeritus of the Johns Hopkins Bloomberg School of Public Health and chairman of the award jury.

Gene
Colour sensitivity can also led to Retinal Diseases/Blindness. Pixabay

One of those honored, Michael Redmond of the National Eye Institute in Maryland, had traced the cause of the disease, Leber congenital amaurosis (LCA), to a mutated gene.

Three cooperating research teams later managed to replace the gene in the eye, restoring vision to treated children and adults with one form of LCA and “enabling the entire field of gene therapy for human disease,” the foundation said.

These teams are comprised of U.S. scientists Jean Bennett and Albert Maguire; Samuel Jacobson and William Hauswirth; and Britons Robin Ali and James Bainbridge.

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Their gene augmentation therapy involved the delivery of healthy genes using engineered harmless viruses, described by the foundation as “an elegant solution.”

The foundation, which focuses on neuroscience and oncology research at its Lisbon base, was set up at the bequest of Portugal’s late industrialist Antonio Champalimaud who died in 2004. The first vision prize was awarded in 2006. (VOA)