#34 Southern Fin Whales Documented, Why Human Reproduction is so Hard and Cells Killing Neurons...
A large group of 150 whales sighted, why human reproduction is so hard and so wasteful as well as research identifying the cells that cause the death of neurons...
Large groups of southern fin whales documented…
Being one of the largest whales in the world, the fin whale has been hunted to near extinction. Following the ban on commercial whaling in 1976, numbers have rebounded. This new study documents data showing 150 southern fin whales in their historic feeding areas - a world first.
Prof Bettina Meyer, biologist at the Alfred Wegener Institute stated how she had “never seen so many whales in one place before and was absolutely fascinated watching these massive groups feed”. Bettina Meyer led an expedition with the research icebreaker Polarstern in the region of the Antarctic Peninsula, during which groups of up to 50 or even 70 fin whales (Balaenoptera physalus quoyi) were observed.
This expedition investigated a few different factors including the effects of climate change on Antarctic krill, which forms the basis of the Antarctic food web, growing up to six centimetres in length. These tiny bioluminescent crustaceans are a key food source for fish, penguins and whales. The research trip utilised an onboard helicopter to count and film whale stocks. Over 22 flights the team covered a total of 3251 kilometres and counted 100 groups of fin whales. Through using a combination of filming and sighting information with acoustic measuring (krill locating), the team were able to identify the swarms of prey as well as how the whales hunted them.
The whales don’t solely eat the krill. Whale excrement fertilises the ocean with the nutrients containing key elements such as iron. This is a comparatively sparse resource in the Antarctic yet essential for the growth of phytoplankton (microalgae) in the water. In turn this is a food source for the krill, demonstrating the full cycle feedback loop.
The recovery of fin whale stock seems to be a trend with subsequent research teams and trips reporting similar sightings. “Even if we still don’t know the total number of fin whales in the Antarctic, due to the lack of simultaneous observations, this could be a good sign that, nearly 50 years after the ban on commercial whaling, the fin whale population in the Antarctic is rebounding,” says Bettina Meyer.
Why is it so hard for humans to have a baby…
The new study from the University of Bath explains why fish embryos are fine but sadly humans’ embryos often don’t survive, with implications for the treatment of infertility. The teams suggests that selfish chromosomes are to blame for human embryos dying very early on.
Roughly half of all fertilised eggs die before a mother even knows that she is pregnant. Many of those that do survive to become a recognised pregnancy will be spontaneously aborted after a few weeks. The team investigated why, despite hundreds of thousands of years of evolution, it is still so comparatively hard for humans to have a baby.
The immediate cause of much of these deaths is that the embryos have the wrong number of chromosomes. Fertilised eggs should have 46 chromosomes, 23 from mum in the eggs, 23 from dad in the sperm.
Professor Hurst, Director of the Milner Centre for Evolution, said: “Very many embryos have the wrong number of chromosomes, often 45 or 47, and nearly all of these die in the womb. Even in cases like Down syndrome with three copies of chromosome 21, about 80% sadly will not make it to term.”
The team identified a number of clues that could indicate why this is the case.
Firstly, when the embryo has the wrong number of chromosomes, it is usually due to mistakes that occur when the eggs are made in the mother, rather than when the sperm is made in the father.
The mistakes happen in the first two steps of egg manufacturing. The first step is vulnerable to mutations that interfere with the process such that the mutation can selfishly sneak into more than 50% of the eggs, forcing the partner chromosome to be destroyed - a process called centromeric drive.
What Hurst noticed was that, in mammals, a selfish mutation that tries to do this but fails, resulting in an egg with one too many or one too few chromosomes, can still be evolutionarily better off. The surviving offspring can actually do better as a result. In mammals, because the mother continuously feeds the developing foetus, it is evolutionary beneficial for the embryo to be lost earlier rather than carried to the full term.
Hurst explained: “This first step of making eggs is odd. One chromosome of a pair will go to the egg the other will be destroyed. But if a chromosome ’knows’ it is going to be destroyed it has nothing to lose, so to speak. Remarkable recent molecular evidence has found that when some chromosomes detect that they are about to be destroyed during this first step, they change what they do to prevent being destroyed, potentially causing chromosome loss or gain, and the death of the embryo. What is remarkable, is that if the death of the embryo benefits the other offspring of that mother, as the selfish chromosome will often be in the brothers and sisters that get the extra food, the mutation is better off because it kills embryos”.
Interestingly fish and amphibians don’t have this problem. In over 2000 fish embryos, not one was found with chromosomal errors from the mum. By contrast, chromosome loss or gain is a problem for every mammal that has been looked at. Hurst commented, “It is a downside of feeding our offspring in the womb. If they die early on, the survivors benefit. It leaves us vulnerable to this sort of mutation.”
Hurst suspects that humans may indeed be especially vulnerable. Due to Humans typically having one baby at a time and the death of an embryo occurring early on, the mother is enabled to reproduce again - she probably never even knew her egg had been fertilised.
Hurst added “I would hope too that these insights will be one step to helping those women who experience difficulties getting pregnant, or suffer recurrent miscarriage.”
💀Death of Neurons
Identifying the cells that cause the death of neurons…
Microglia are the resident macrophages of the central nervous system. They are primarily responsible for neuronal death in Leigh syndrome and the neurological symptoms that result from this mitochondrial disease.
Leigh syndrome is the most common of the mitochondrial diseases. The cause of this group of diseases is the malfunction of mitochondria through mutations in the mitochondrial RNA or cellular DNA. In Leigh syndrome, organs and tissues that need more energy such as muscles or the brain cannot function normally causing both motor and respiratory problems.
This new study found that inflammation causes neuronal death and that the main culprits in the process are microglia cells. These cells which under normal conditions are responsible for defending the nervous system, actually attack neurons with mitochondrial dysfunction, causing their death.
The researchers analysed the effect of suppression of microglia cells by a drug; Pexidartinib (PLX-3397). “With the removal of microglia the motor problems took longer to appear and life expectancy was longer. In addition, when studying their brains we found that there was much less neuronal loss ", explains Kevin Aguilar , first author of the article. He added that "This drug, while not a good candidate for treating the disease, has been a key tool in identifying the effect of the neuroinflammation process and understanding how neuronal loss occurs".
As well as this drug, the study looked at the role of IL-6, a protein that modulates inflammatory activity and guides microglia activity. “We suspected that this protein would also play a key role in the symptomatology of the syndrome. That’s why we wanted to analyse what happened when there was a deficiency. Contrary to what we expected, however, although respiratory problems were reduced, the effects were very moderate. This makes us think that there are other proteins involved ", explains Aguilar .
"Our next goal will be to describe the specific process by which microglia cells attack neurons and thus be able to develop more specific and selective treatments in the future," he concludes.
🦠 Disease and Illness
📷 Weekly Camera Roll
Click on the text below to keep reading…
Content may be adapted and edited for style and length.
Herr, H., Viquerat, S., Devas, F., Lees, A., Wells, L., Gregory, B., Giffords, T., Beecham, D. and Meyer, B., 2022. Return of large fin whale feeding aggregations to historical whaling grounds in the Southern Ocean. Scientific Reports, 12(1).
Press Release: https://www.awi.de/en/about-us/service/press/single-view/150-wale-beim-gemeinsamen-fressen-beobachtet.html
Hurst, L., 2022. Selfish centromeres and the wastefulness of human reproduction. PLOS Biology, 20(7), p.e3001671.
Press Release: https://www.bath.ac.uk/announcements/why-is-it-so-hard-for-humans-to-have-a-baby/
💀Death of Neurons
Aguilar, K., Comes, G., Canal, C., Quintana, A., Sanz, E. and Hidalgo, J., 2022. Microglial response promotes neurodegeneration in the <scp> <i>Ndufs4 KO</i> </scp> mouse model of Leigh syndrome. Glia,.
Press Release: https://www.uab.cat/web/sala-de-premsa/detall-noticia/identifiquen-les-cel-lules-que-provoquen-la-mort-de-les-neurones-en-un-model-animal-de-malaltia-mitocondrial-1345829508832.html?detid=1345864303519
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