Tag Archives: Biology

The Ediacaran Enigma

In biology, there’s a metaphor known as the universal tree of life that expresses the idea that all organisms are part of a big happy family, descending and evolving from the same common ancestor. It’s proved to be a pretty good rule of thumb too, as analysis has given most organisms a place somewhere in the branches of this metaphorical tree. Now, pay attention to how I emphasized “most”, because there’s an exception to this rule – one group of puzzling animals, known only from fossils, that has defied scientists’ attempts to place them on the tree of life and relate them to other organisms. They are the Ediacaran animals – grouped together and named after the period of Earth’s history they lived in (likely because “what the hell are these things” wasn’t very scientific).

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Artist’s impression of an aquatic Ediacaran environment. Image Credit: Smithsonian National Museum of Natural History via Flickr (CC BY-SA 2.0)

Eloquently described by the scientific community as looking like “mud-filled bags” or “quilted mattresses”, these bizarre animals first appeared in our fossil record about 600 million years ago, and are the earliest known multicellular organisms. Yet despite being the first, Ediacarans share no clear relationship with later multicellular life, or any other known life for that matter. Usually related organisms have at least some distinctive trait in common (for example, all Cnidarians have stinging cells), but while some Ediacaran animals shared a few passing similarities with sponges or jellyfish, for the most part they were too different from pretty much anything that came before or after them to be considered related to them: they were too complex and large compared to life before them, yet they also had body shapes that were completely alien compared to any forms of life after them. As a result, Ediacaran life is often described as “enigmatic” – or scientist speak for “really weird”.

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Dickinsonia costata, an iconic Ediacaran organism. Note “quilted” appearance. Image Credit: Wikimedia Commons (CC BY 2.5)

Further hammering home the strangeness, despite fossils of Ediacaran organisms being found practically everywhere, all Ediacarans abruptly vanished from the fossil record 540 million years ago, and no-one is entirely sure why.

In short, these multicellular organisms suddenly showed up, disappeared just as suddenly, and are so unrelentingly bizarre that they can’t be definitively linked to any other lifeforms we’ve seen on this planet.

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Paleontologist Guy Narbonne examining Ediacaran fossils at Mistaken Point Ecological Reserve, Newfoundland, Canada. Image Credit: Wikimedia Commons (CC BY 2.0)

Now, before you scream “aliens!” at me, there are actually some reasonable hypotheses as to what the heck Ediacaran life was, why it has no clear relationship to other known life, and why it just disappeared. For example, one hypothesis suggests that the Ediacarans were a “failed experiment” in multicellular life by Mother Nature, having been out-competed to death by later life evolved from unrelated lifeforms (in fact, scientists have traced the origins of modern animals back to the Cambrian explosion, an event that coincidentally happened… wait for it… 541 million years ago). Regardless, given the “we can’t ever know for sure” nature of prehistoric biology, it’s likely that Ediacaran life will remain an intriguing biological mystery for years to come (and my personal favourite footnote in our otherwise fairly predictable biological history).

~ Kimberly

Key protein in spinal cord regeneration found

Researchers at Duke University have identified a key protein used in spinal cord regeneration in zebrafish. The findings were presented in the November 4 edition of the Science journal.

An adult female zebrafish. Authorized for redistribution by the copyright holder. Retrieved from https://en.wikipedia.org/wiki/Zebrafish.

An adult female zebrafish. Authorized for redistribution by the copyright holder. Retrieved from https://en.wikipedia.org/wiki/Zebrafish.

While zebrafish can completely regenerate their spinal cords even after it is severed, humans cannot. This makes spinal cord injuries (SCI) one of the most debilitating injuries for humans, as ability to walk and sense can be impaired. As SCI can be permanent, many patients require lifelong assistance with daily activities, resulting in loss of autonomy.

Diagram of the spinal cord. Image in the public domain; retrieved from https://en.wikipedia.org/wiki/Spinal_cord_injury

Diagram of the spinal cord. Image in the public domain.

When a zebrafish’s spinal cord is undergoing regeneration, a bridge forms. The first cells (a cell is the basic functional unit of all living things) project lengths many times their own size and connect a wide length of the injury. This is followed by nerve cells, and after eight weeks, new nerve tissue has filled the gap formed by the injury, reversing the zebrafish’s paralysis.

Nerve cells in the brain. Shared under the Creative Commons license. Retrieved from https://en.wikipedia.org/wiki/Neuron.

Nerve cells in the brain. Shared under the Creative Commons license. Image by UC Regents Davis campus.

The researchers looked for genes (the basic functional units, made up of DNA, that instruct the body how to make proteins) whose activities changed throughout this process, and they focused on a protein called connective tissue growth factor (CTGF), as they found more of it in the supporting cells (glia) that formed the bridge within two weeks of the injury than before.

Glial cells in a rat brain. Public domain. Retrieved from https://en.wikipedia.org/wiki/Neuroglia.

Glial cells in a rat brain. Public domain.

This finding is important because it provides a direction for research in achieving full recovery of function in patients with SCI. Although the researchers say that CTGF alone will probably not be enough for spinal cord regeneration due to scar tissue (new tissue that forms after injuries) in mammals, now that CTGF has been identified as a key protein for regeneration, it could be used with other proteins and therapies. The researchers expect that studies on CTGF will move towards mammals like mice.

In addition, knowing this new information about CTGF can lead research towards similar proteins. Indeed, the researchers themselves have indicated plans to study the other secreted proteins they observed when looking for genes with altered activities throughout the zebrafish’s healing process.

Permanent SCI have debilitating physical and psychological effects on their patients, their families, and the support system around them. An estimated 24-45% of people with SCI suffer from depression, and the suicide rate can be as great as six times of the general population. In fact, in young people with SCI, it is suicide that is the leading cause of death and not physical complications of the injury itself. The psychological impact is tragic, which is one of the reasons why I believe that improving patient outcomes for SCI is one of the most pressing needs for modern medicine, and also why I hope research funding continues to go towards spinal cord research.

-Jasper Yoo

We Found Life in a Hopeless Place

What characteristics come to mind when one imagines a planet capable of supporting life? One would probably think of modern-day Earth: with our nice liquid water, plate tectonics, and comfy atmosphere, it’s a pretty sweet place to live, 2016 US election cycle notwithstanding. But there’s no denying our dear mother Earth has mellowed out over the years: the geological era spanning Earth’s infancy – lasting from the time of its formation approximately 4.6 billion years ago to around 4 billion years ago – is called the Hadean eon (after the Greek god of the underworld), and for good reason. During this period, the Earth’s crust was unstable, its surface was partially molten and constantly bombarded by other celestial objects, and its atmosphere was thick with gases toxic to most organisms today.

An artist's concept of the young Earth being bombarded by asteroids.

Artist’s impression of Hadean Earth. Image Credit: NASA’s Goddard Space Flight Center Conceptual Image Lab; Attribution: CC BY 2.0

Scientists long believed that the beginning of life on Earth could not have occurred during this hellish, inhospitable period of the planet’s history – that Hadean Earth was too molten, too devoid of liquid water to support life. The beginning of life was instead speculated to have occurred 3.8 billion years ago, within the Archean eon (the geological era directly following the Hadean) during which Earth had cooled such that the crust and by extension, liquid water oceans, could actually exist in a form stable enough to allow for life to form.

That is, until 2015.

Analysis of 4.1-billion-year-old zircon crystals – in other words, originating from the Hadean era – though preliminary, has cast doubts on the depiction of early Earth as being desolate and lifeless.

Jack Hills, Australia - where the Hadean zircon crystals were found. Image Credit: NASA image by Robert Simmon, based on Landsat data provided by the Global Land Cover Facility

Jack Hills, Australia – where the Hadean zircon crystals were found. Image Credit: NASA image by Robert Simmon, based on Landsat data provided by the Global Land Cover Facility; Attribution: Public Domain

You see, these zircon crystals act as miniature time capsules of sorts – they captured some surrounding material during their formation that was then preserved as impurities in the crystals. Upon studying the contents of these impurities, researchers from the University of California, Los Angeles discovered something startling – a form of carbon almost exclusively associated with organic matter, specifically photosynthetic life. The kicker? Researchers have concluded that the carbon is even older than the 4.1-billion-year-old zircon that houses it.

So what does this mean for our understanding of Earth’s history, as well as life and its beginnings? Well, for geologists, these “traces of life” might indicate that the Hadean era may not have been as fire and brimstone as once believed – that Earth might have cooled down earlier than previously predicted. For biologists, these traces might indicate that life can be supported in conditions harsher than once thought possible. For yet others (particularly those interested in extraterrestrial life), the possibility that life could have arisen on Earth so soon after its formation invites thoughts that are excellently summarized by the reaction of another scientist in the same field of study: “if life arose relatively quickly on Earth … then it could be common in the universe.

~ Kimberly Truong