Risk of congenital heart disease is determined by the age of the mother, not her eggs

As a woman of child-bearing age, I am acutely aware that the longer I postpone having children, the greater the risk that my future offspring may have a medical or developmental disorder. It seems like every few weeks, a new study makes it into the news cycle linking advanced maternal age to disease X or condition Y. (Men don’t get off scotch free – recent studies have linked advanced paternal age to autism.) A study published in Nature this week has shed light on maternal age-associated risk of congenital heart disease and risk-modifying factors.

Despite advances in diagnoses and treatment, congenital heart disease remains one of the leading causes of childhood illness and mortality. Roughly one in 100 children will have minor congenital heart disease whereas one in 1000 will require heart surgery. The risk factors for congenital heart disease include genetics, infections, maternal diabetes and advanced maternal age. A team of researchers led by Dr. Patrick Jay at Washington University School of Medicine asked whether the maternal age effect was based on the age of the mother’s eggs or the mother herself.

To tease apart these scenarios, the researchers carried out reciprocal ovarian transplants where the ovaries of young mice were transplanted into older mice and vice versa. Young mice were less than 100 days old whereas old mice were on average 318 days old (lab mice live on average two and a half years or roughly 850 days). They compared what proportion of the offspring of these two groups of mice had congenital heart disease by looking for ventricular septal defects (VSD). Ventricular septal defects are a common birth defect of the heart where there is a hole in the wall separating the lower chambers of the heart. The offspring of older mothers with young ovaries developed VSD significantly more frequently than the offspring of young mothers with old ovaries. This result provides compelling evidence that the risk of congenital heart disease is associated with the increased age of the mother and not of her eggs. Continue reading

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How whales lost their sense of smell and taste

humpback-whale-436115_1280

Whales are very likeable creatures. They are highly intelligent, sentient and social. But without a doubt, they would make terrible chefs and untrustworthy food critics. It seems that somewhere along the evolutionary path, whales lost their sense of smell and much of their sense of taste.

Baleen whales are some of the largest animals in the world and spend most of their time below the water surface, making them difficult to find and even more difficult to study. The group of Japanese researchers at Kyoto University worked around these challenges by using genome sequencing and fossil records to study the evolution of smell and taste in toothed and baleen whales. The researchers isolated DNA from minke whale meat purchased at a fish market and sequenced it to assemble the entire genome of the minke whale. For comparison, they also used the previously sequenced genomes of the bottlenose dolphin, a toothed whale, and cow, which, along with pigs and hippos, belongs to the same clade as cetaceans.

In mammals, odours in the air are detected by different receptors in our nasal cavity. When they compared the whale genomes to the cow genome, the researchers found that both whale genomes had lost a large number of genes required for odour detection. The most notable of these is the family of genes known as olfactory receptors (OR). The cow genome contained over 900 functional OR genes while the minke whale and dolphin genomes contained just 70 and 12, respectively. Mice, with their keen sense of smell, have over 1000 OR genes. Continue reading

You are what you eat: new evidence shows that sea slugs carry algal gene

One of the most commonly touted attributes of science is that its ability to self-correct. New models and theories are constantly being generated based on experimental results but just as frequently, these new theories and ideas are challenged and sometimes, proven to be wrong by other scientists. Encouragingly, this type of academic rigor is not exclusively applied to high-impact research (recently examples include a deceptively simple method to create stem cell and a bacteria that uses arsenic to build its DNA) but also to the seemingly insignificant curiosities of life. The case of the green sea slug falls into this latter category.

Green sea slugs get their vibrant emerald green colour from the algae that they eat, specifically from the chloroplasts contained within the algae. Chloroplasts are specialized compartments in plant cells that house all of the machinery required for photosynthesis. Think of them as little solar panels, converting sunlight into the energy plants need to grow. Green sea slugs are able to extract chloroplasts from algae and store them in special cells along their digestive tract. In some cases, chloroplasts are stored for more than nine months! For a long time, scientists believed that the main role of these chloroplasts was to generate energy for their new slug hosts by photosynthesis. This finding generated a lot of hype and understandably so. Green sea slugs are one of a small handful of animal species that can photosynthesize and quickly became known as “solar-powered slugs” and “leaves that crawl”.

The green sea slug Elysia chlorotica (Source)
The green sea slug Elysia chlorotica (Source)

In 2014, the idea that green sea slugs use their chloroplasts exclusively to generate energy through photosynthesis was challenged when a group of researchers found that blocking photosynthesis had no effect on weight loss or survival rate of green sea slugs during starvation. If the main purpose of chloroplasts was to generate energy for the slugs during starvation, then blocking photosynthesis should lead to lower survival and more weight loss. Based on these new findings, the researchers proposed a new theory for why green sea slugs hoard so many chloroplasts. Instead of using them as solar panels to create energy, the sea slugs are breaking down the chloroplasts into its many components and eating those parts as food. Maybe green sea slugs store chloroplasts for the same reason that bears store fat and squirrels store nuts before winter hibernation. This is not to say that green sea slugs don’t photosynthesize. They are undoubtedly capable of photosynthesizing and may use it to some extent to survive periods of starvation but just how significant of a contribution that is remains to be seen. Continue reading