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A Second X Chromosome Could Explain Why Women Live Longer Than Men

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Researchers say that women may be born with an advantage when it comes to longevity. (Credit: Pressmaster/Shutterstock.com)

Women have an average life expectancy that’s about 4 years longer than men’s – regardless of culture or geography. Even among animal species, females outlive males.

Why females have an advantage in the longevity department hadn’t been well understood. In the past, some had assumed it had to do with lifestyle. But scientists say there may be a genetic mechanism underlying this age-old phenomenon. In a new study, researchers found that mice with two X chromosomes lived longer, regardless of other biological factors. Researchers say the finding suggests the second X chromosome may govern longevity and explain why women outlive men.

X Marks Longer Lifespans

All mammals are born with two sex chromosomes. Females have two X chromosomes, whereas males have one X and one Y. X chromosomes are necessary for survival and contain important genes related to the brain. Y chromosomes, on the other hand, are found only in males and are not crucial for survival. Y chromosomes carry relatively few genes beyond those related to secondary sex characteristics such as male genitals and facial hair.

To investigate the link between chromosomes and survival, researchers tested different chromosome and gonad combinations among genetically identical mice. Some mice had biological male or female combinations mirroring those found in nature — XX with ovaries and XY with testes. Other mice had XX chromosomes paired with testes and XY chromosomes paired with ovaries.

Researchers found that mice with natural female mouse biology — two X-chromosomes and ovaries — outlived all the mice. But mice with two X-chromosomes tended to live longer, regardless of whether they had ovaries or testes. Among this group of mice, the longevity effect was observed beginning at 21 months, which is at the end of a normal mouse lifespan. Researchers say the results point to a potential role of the second X chromosome in longer lifespans.

“This suggests that the hormones produced by female gonads increase lifespan in mice with two X chromosomes, either by influencing how the mouse develops or by activating certain biological pathways during their lives,” said Dena Dubal, a neurologist and senior author of the study published in Aging Cell.

Scientists don’t understand exactly why the second X chromosome contributes to a longer lifespan. It may be that the second X and its genetic expression has a protective effect that increases survival. Another theory is that the presence of a Y chromosome is somehow harmful. However, the scientists hope to understand this interplay by embarking on future chromosonal studies.

“When things go wrong in aging, having more of the X chromosome, along with its diversity of expression, could be really beneficial,” Dubal said.

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Ecology

Today’s letters: ‘Visionary’ plans don’t always work in Ottawa

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The opinion piece written by Tobi Nussbaum, CEO of the NCC, declares that a “bold, visionary transit plan” would showcase the capital.

As a long-term resident of Ottawa, I’ve had it with visionary plans. In the 1950s, the streetcars serving Ottawa so well were sent to the scrapyards. In the early ’60s, Queensway construction bulldozed established neighbourhoods and ripped the city apart. Later in the decade, the downtown railway station, which could have formed the hub of a commuter network, was relocated to the suburbs. These actions, in the name of “progress,” were undertaken with the “vision” to make Ottawa a car-reliant city.

Now we have an LRT, built just in time for most people to realize that they do not have to go downtown as they can work from home.

Current thinking is pushing a new “link” between Ottawa and Gatineau, with yet more expensive and disruptive infrastructure projects being touted, including a tramway or another tunnel under the downtown core.

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Ecology

That was then: Biggest earthquake since 1653 rocked Ottawa in 1925

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A regular weekly look-back at some offbeat or interesting stories that have appeared in the Ottawa Citizen over its 175-year history. Today: The big one hits.

The Ottawa Senators were playing a Saturday night game against the Montreal Canadiens at the Auditorium, the score tied 0-0 halfway through the second period. Sens’ rookie Ed Gorman and the Habs’ Billy Boucher had just served penalties for a dustup when the building began to make “ominous creaking sounds.” A window crashed to the ground.

Nearby, at Lisgar Collegiate, all eyes were on teenager Roxie Carrier, in the role of Donna Cyrilla in the musical comedy El Bandido. She had the stage to herself and was singing “Sometime” when the building rocked, the spotlight went out, and someone in the audience yelled “Fire!”

At a home on Carey Avenue, one woman’s normally relaxed cat suddenly arched its back, rushed around the room two or three times, spitting angrily, and climbed up the front-window curtains.

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Ecology

Ottawa delays small nuclear reactor plan as critics decry push for new reactors

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TORONTO — Canadians will have to wait a little while longer to see the federal government’s plan for the development of small nuclear reactors, seen by proponents as critical to the country’s fight against global warming.

Speaking at the opening of a two-day virtual international conference on Wednesday, the parliamentary secretary to the minister of natural resources said the plan will lay out key actions regarding the reactors. Its launch, Paul Lefebvre said, would come in the next few weeks.

“We’re still putting the finishing touches on it,” Lefebvre said. “The action plan is too important to be rushed.”

Small modular reactors — SMRs — are smaller in size and energy output than traditional nuclear power units, and more flexible in their deployment. While conventional reactors produce around 800 megawatts of power, SMRs can deliver up to 300 megawatts.

Proponents consider them ideal as both part of the regular electricity grid as well as for use in remote locations, including industrial sites and isolated northern communities. They could also play a role in the production of hydrogen and local heating.

“SMRs will allow us to take a bold step of meeting our goal of net-zero (emissions) by 2050 while creating good, middle class jobs and strengthening our competitive advantage,” said Lefebvre.

Natural Resources Minister Seamus O’Regan had been scheduled to speak at the conference but did not due to a family emergency.

Industry critics were quick to pounce on the government’s expected SMR announcement. They called on Ottawa to halt its plans to fund the experimental technology.

While nuclear power generation produces no greenhouse gas emissions, a major problem facing the industry is its growing mound of radioactive waste. This week, the government embarked on a round of consultations about what do with the dangerous material.

Dozens of groups, including the NDP, Bloc Quebecois, Green Party and some Indigenous organizations, oppose the plan for developing small modular reactors. They want the government to fight climate change by investing more in renewable energy and energy efficiency.

“We have options that are cheaper and safer and will be available quicker,” Richard Cannings, the NDP natural resources critic, said in a statement.

Lefebvre, however, said the global market for SMRs is expected to be worth between $150 billion and $300 billion a year by 2040. As one of the world’s largest producers of uranium, Canada has to be part of the wave both for economic and environmental reasons, he said.

“There’s a growing demand for smaller, simpler and affordable nuclear technology energy,” Lefebvre said.

Joe McBrearty, head of Canadian Nuclear Laboratories, told the conference the company had signed a host agreement this week with Ottawa-based Global First Power for a demonstration SMR at its Chalk River campus in eastern Ontario. A demonstration reactor will allow for the assessment of the technology’s overall viability, he said.

“When talking about deploying a new technology like an SMR, building a demonstration unit is vital to the success of that process,” McBrearty said. “Most importantly, it allows the public to see the reactor, to kick the tires so to speak, and to have confidence in the safety of its operation.”

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