28 October 2008

Sea urchin secrets: biomineralization and other discoveries

We can learn much from the immortal sea urchin! A recent study of how sea urchins produce their spines has shed more light on biomineralization, that in turn can be applied in new microelectronic devices or medical uses.
Pencil sea urchins
A sea urchin spine is a single crystal from base to tip! The crystal is a material that is the strongest and most durable in the animal world. It is made using the most readily available elements in sea water: calcium, oxygen and carbon.

Another earlier study of how broken spines were replaced, found that the material of the spines is first amassed in a non-crystalline form, called "amorphous calcium carbonate" (ACC). Packets of ACC are shoveled out of the cells surrounding the base of a broken spine and up to the growing end. Within hours of arriving in place, the amorphous material, which is composed of densely packed, but disorganized molecules, turns to calcite crystal.

Immortal urchins: Other cool urchin features include the discovery that some can live for 200 years. Not only that, these old ones continue to breed. In fact, the ancient ones are more prolific breeders!

Sea urchins are like us! (or we are like urchins) The genome of the purple sea urchin (Strongylocentrotus purpuratus) was sequenced last year and it was found that it has 7,000 genes in common with humans, including genes associated with Parkinson's, Alzheimer's and Huntington's diseases and muscular dystrophy. Sea urchins share a common ancestor with humans. Sea urchins are closer to human and vertebrates from an evolutionary perspective than other more widely studied animal models, such as fruit fly or worms.

Sea Urchin Yields A Key Secret Of Biomineralization
ScienceDaily 27 Oct 08;
The teeth and bones of mammals, the protective shells of mollusks, and the needle-sharp spines of sea urchins and other marine creatures are made-from-scratch wonders of nature.

Used to crush food, for structural support and for defense, the materials of which shells, teeth and bones are composed are the strongest and most durable in the animal world, and scientists and engineers have long sought to mimic them.

Now, harnessing the process of biomineralization may be closer to reality as an international team of scientists has detailed a key and previously hidden mechanism to transform amorphous calcium carbonate into calcite, the stuff of seashells. The new insight promises to inform the development of new, superhard materials, microelectronics and micromechanical devices.

In a report Oct. 27 in the Proceedings of the National Academy of Sciences, a group led by University of Wisconsin-Madison physicist Pupa Gilbert describes how the lowly sea urchin transforms calcium carbonate — the same material that forms "lime" deposits in pipes and boilers — into the crystals that make up the flint-hard shells and spines of marine animals. The mechanism, the authors write, could "well represent a common strategy in biomineralization…."

"If we can harness these mechanisms, it will be fantastically important for technology," argues Gilbert, a UW-Madison professor of physics. "This is nature's bottom-up nanofabrication. Maybe one day we will be able to use it to build microelectronic or micromechanical devices."

Gilbert, who worked with colleagues from Israel's Weizmann Institute of Science, the University of California at Berkeley and the Lawrence Berkeley National Laboratory, used a novel microscope that employs the soft-X-rays produced by synchrotron radiation to observe how the sea urchin builds its spicules, the sharp crystalline "bones" that constitute the animal's endoskeleton at the larval stage.

Similar to teeth and bones, the sea urchin spicule is a biomineral, a composite of organic material and mineral components that the animal synthesizes from scratch, using the most readily available elements in sea water: calcium, oxygen and carbon. The fully formed spicule is composed of a single crystal with an unusual morphology. It has no facets and within 48 hours of fertilization assumes a shape that looks very much like the Mercedes-Benz logo.

These crystal shapes, as those of tooth enamel, eggshells or snails, are very different from the familiar faceted crystals grown through non-biological processes in nature. "To achieve such unusual — and presumably more functional — morphologies, the organisms deposit a disordered amorphous mineral phase first, and then let it slowly transform into a crystal, in which the atoms are neatly aligned into a lattice with a specific and regular orientation, while maintaining the unusual morphology," Gilbert notes.

The question the Wisconsin physicist and her colleagues sought to answer was how this amorphous-to-crystalline transition occurs. The sea urchin larval spicule is a model system for biominerals, and the first one in which the amorphous calcium carbonate precursor was discovered in 1997 by the same Israeli group co-authoring the current PNAS paper. A similar amorphous-to-crystalline transition has since been observed in adult sea urchin spines, in mollusk shells, in zebra fish bones and in tooth enamel. The resulting biominerals are extraordinarily hard and fracture resistant, compared to the minerals of which they are made.

"The amorphous minerals are deposited and they are completely disordered," Gilbert explains. "So the question we addressed is 'how does crystallinity propagate through the amorphous mineral?'"

To answer it, Gilbert and her colleagues observed spicule development in 2- to 3-day-old sea urchin larvae. The sea urchin spicule is formed inside a clump of specialized cells and begins as the animal lays down a single crystal of calcite in the form of a rhombohedral seed, from which the rest of the spicule is formed. Starting from the crystalline center, three arms extend at 120 degrees from each other, as in the hood ornament of a Mercedes-Benz. The three radii are initially amorphous calcium carbonate, but slowly convert to calcite.

"We tried to find evidence of a massive crystal growth, with a well defined growth front, propagating from the central crystal through the amorphous material, but we never observed anything like that," Gilbert says. "What we found, instead, is that 40-100 nanometer amorphous calcium carbonate particles aggregate into the final morphology. One starts converting to crystalline calcite, then another immediately adjacent converts as well, and another, and so on in a three-dimensional domino effect. The pattern of crystallinity, however, is far from straight. It resembles a random walk, or a fractal, like lightning in the sky or water percolating through a porous medium," explains Gilbert.

The new work, according to Gilbert, brings science a key step closer to a thorough understanding of how biominerals form and transform. Knowing the step-by-step process may permit researchers to develop new crystal structures that can be used in applications ranging from new microelectronic devices to medical applications.

The new study was funded by the National Science Foundation and the U.S. Department of Energy.

How The Sea Urchin Grows New Spines
ScienceDaily 22 Nov 04;
The sea urchin's tough, brittle spines are an engineering wonder. Composed of a single crystal from base to needle-sharp tip, they grow back within a few days after being broken off. Now, a team of scientists at the Weizmann Institute of Science has shown how they do it.

While many crystals grow from component atoms or molecules that are dissolved in liquid, sugar and salt being the most familiar examples, the team of Profs. Lia Addadi and Steve Weiner, of the Institute's Structural Biology Department, found that the sea urchin uses another strategy. The material of the spines is first amassed in a non-crystalline form, termed "amorphous calcium carbonate" (ACC). Packets of ACC are shoveled out of the cells surrounding the base of the broken spine and up to the growing end. Within hours of arriving in place, the amorphous material, which is composed of densely packed, but disorganized molecules, turns to calcite crystal in which the molecules line up evenly in lattice formations.

Working with graduate student Yael Politi and Eugenia Klein and Talmon Arad of the Chemical Research Support Unit, Professors Addadi and Weiner used four different methods of investigation, including two kinds of electron microscopy, to look for the ACC as it was being deposited and turning to crystal. "The question," says Weiner "is why it should be so difficult to observe a process that seems to be so basic. Scientists have been studying it for over a hundred years. In fact, because the ACC is a transient phase, we had to develop new methods to catch it while it exists."

The captured images show microscopic needles that grow first straight out from the stump of the old spine, and then branch out to form a lacy structure that is hard but light. The crystalline structure of the old spine provides the template for the alignment of the molecules in the crystal, and thus controls the intricate, yet precise, growth pattern.

Though previous studies by the Weizmann group have shown the same strategy is used by immature sea urchins and mollusks in the larval stage to build internal skeletons, this is the first time that the process was observed in adult marine animals. It is far from obvious that larva and adult would use the same methods – their lifestyles are very different. For instance, the tiny sea urchin larva is transparent and swims around, while the round, spiky adult lives on the sea floor. This can translate into differences in biological processes, as well.

Because it works for both, Addadi and Weiner believe this method is probably a basic strategy used not only by close relatives of the sea urchin such as sea stars, but by a wide variety of spiny and shelled sea creatures like mollusks and corals. In addition, the idea of growing single crystals by first creating the material in an amorphous phase might prove useful to material scientists and engineers who want to produce and shape sophisticated synthetic materials that have the properties of single crystals.

Prof. Addadi's research is supported by the J & R Center for Scientific Research, the Ilse Katz Institute for Material Sciences and Magnetic Resonance Research, the Helen and Milton A. Kimmelman Center for Biomolecular Structure and Assembly, the Philip M. Kltuznick Fund for Research, the Minerva Stiftung Gesellschaft fuer die Forschung m.b.H., the Women's Health Research Center and the Ziegler Family Trust, Encino, CA. She holds the Dorothy and Patrick Gorman Professional Chair.

Red Sea Urchins Found To Live Up To 200 Years
ScienceDaily 6 Nov 93;
CORVALLIS, Ore. – A new study has concluded that the red sea urchin, a small spiny invertebrate that lives in shallow coastal waters, is among the longest living animals on Earth – they can live to be 100 years old, and some may reach 200 years or more in good health with few signs of age.

In other words, an individual red sea urchin that hatched on the day in 1805 that Lewis and Clark arrived in Oregon may still be thriving – and even breeding.

The research was just published in a professional journal, the U.S. Fishery Bulletin, by scientists from Oregon State University and the Lawrence Livermore National Laboratory. It may have important implications for management of a commercial fishery and our understanding of marine biology, as well as challenge some erroneous assumptions about the life cycle of this never-say-die marine species.

It used to be believed that red sea urchins lived to be only seven to 15 years of age, experts say. But the newest findings are based on the use of two completely different techniques of determining sea urchin ages – one biochemical and the other nuclear - that produced the same results. The studies show red sea urchins can have a vast lifespan surpassing that of virtually all terrestrial and most marine animal species, and seem to show almost no signs of senescence, or age-related dysfunction, right up until the day that something kills them.

"No animal lives forever, but these red sea urchins appear to be practically immortal," said Thomas Ebert, a marine zoologist at OSU. "They can die from attacks by predators, specific diseases or being harvested by fishermen. But even then they show very few signs of age. The evidence suggests that a 100-year-old red sea urchin is just as apt to live another year, or reproduce, as a 10-year-old sea urchin."

The more mature red sea urchins, in fact, appear to be the most prolific producers of sperm and eggs, and are perfectly capable of breeding even when incredibly old. There is no sea urchin version of menopause.

Some of the new studies on this species were done with funding support from the Pacific States Fishery Commission to gain more information about the species, its life cycle, biology, survival rate, growth patterns, and perhaps shed light on why the red sea urchin resource was declining in some areas.

This small marine animal, which is found in shallow Pacific Ocean coastal waters from Alaska to Baja California and also elsewhere in the world's oceans, lives by grazing quietly on marine plants and deterring most predators with its pointy spines. Historically, it had been considered a nuisance.

"In the U.S. in the 1960s, sea urchins were considered the scourge of the sea, a real menace," Ebert said. "They ate plants in kelp forests and people believed they were at least partly responsible for the decline of that marine ecosystem, so they tried to poison them, get rid of them however possible."

But in the 1970s a commercial fishery developed in the U.S. based on sea urchins, which were sold primarily to Japan where their sex organs were considered a delicacy. They brought high prices, and at one point in the 1990s were one of the most valuable marine resources in California.

Ebert did some early work on the red sea urchin, along with colleagues Steve Schroeter at the University of California, Santa Barbara, and John Dixon, of the California Coastal Commission. It quickly became apparent that sea urchins, among other things, grew a lot more slowly and lived a lot longer than had been believed.

"Sea urchins live as male and females, and fertilization of eggs takes place while they float in the ocean," Ebert said. "The larvae then feed for a month or more before turning into tiny sea urchins."

The red sea urchin, in fact, does grow fairly quickly when it's young – at the age of two years, it can grow from two centimeters to four centimeters in one year, doubling its size. But even at that, it still takes at least 6-7 years before the sea urchin is of harvestable size, the scientists say, compared to the two years that had previously been believed.

By the time the sea urchin is a teenager, its growth slows dramatically. And at the age of 22, researchers found it grew each year from about 12 centimeters to only 12.1 centimeters. But somewhat remarkably, it appears to never really stop growing. It's just very, very slow.

"Some of the largest and we believe oldest red sea urchins up to 19 centimeters in size have been found in waters off British Columbia, between Vancouver Island and the mainland," Ebert said. "By our calculations they are probably 200 or more years old."

The first studies indicating these ages was done with tagging of individual sea urchins and injection with tetracycline, which becomes incorporated into the sea urchin skeleton and can be used to track the growth rates. The latest work, which was just published, used measures of carbon-14, which has increased in all living organisms following the atmospheric testing of atomic weapons in the 1950s.

"Radiocarbon testing in this type of situation provided a very strong and independent test of growth rates and ages," Ebert said. "Among other things, it confirmed that in older sea urchins there is a very steady, very consistent growth that's quite independent of ocean conditions or other variables, and once they near adult size our research indicates they do not have growth spurts. With this species, it's pretty simple. The bigger they are, the older they are."

The research was done with red sea urchins, Ebert said, but may be at least partly relevant to other sea urchin species.

The study suggests, among other things, that this invertebrate species has a fairly poor ability to survive various threats during the first year of life and reach reproductive age. Otherwise there would be a great many more sea urchins.

Older sea urchins can help provide more young and therefore may play a key role in creating a sustainable fishery, so a return to harvest policies that limits harvest above a certain size might be prudent, the researchers said.

Sea Urchin Genome Suprisingly Similar To Man And May Hold Key To Cures
ScienceDaily 7 Dec 07;
Sea urchins are small and spiny, they have no eyes and they eat kelp and algae. Still, the sea creature's genome is remarkably similar to humans' and may hold the key to preventing and curing several human diseases, according to a University of Central Florida researcher and several colleagues.

UCF Professor Cristina Calestani was part of the Sea Urchin Genome Sequencing Group, which recently completed sequencing of the sea urchin genome and published its findings in the November issue of Science. The National Institutes of Health funded most of the nine-month project.

The genome of the purple sea urchin is composed by 814 "letters" coding for 23,300 genes.

Sea urchins are echinoderms, marine animals that originated more than 540 million years ago. The reason for the great interest in sequencing the sea urchin genome is because it shares a common ancestor with humans. Sea urchins are closer to human and vertebrates from an evolutionary perspective than other more widely studied animal models, such as fruit fly or worms. The purple sea urchin, in fact, has 7,000 genes in common with humans, including genes associated with Parkinson's, Alzheimer's and Huntington's diseases and muscular dystrophy.

"Another surprise is that this spiny creature with no eyes, nose or hears has genes involved in vision, hearing and smell in humans," Calestani said. "The comparison of human genes with their corresponding ancestral sea urchin genes may give important insight on their function in humans, in the same way the study of history helps understanding the reality of our modern world."

The genome sequencing project was led by Erica Sodergren and George Weinstock at the Baylor College of Medicine-Human Genome Sequencing Center in Houston, along with Dr. Richard Gibbs, director of the Baylor center, and Drs. Eric Davidson and Andrew Cameron at the California Institute of Technology.

Of particular interest to Calestani is the way the sea urchin's immune system works. The human immune system has two components: innate immunity, with which we are born, and acquired immunity, which is the ability to produce antibodies in response to an infection. Sea urchins only have innate immunity, and it is greatly expanded with 10 to 20 times as many genes as in human.

"Considering that sea urchins have a long life span -- some can live up to 100 years -- their immune system must be powerful," Calestani said. "Sea urchins could very well provide a new set of antibiotic and antiviral compounds to fight various infectious diseases."

The sea urchin has been used for many years as a research model to study embryonic development.

Cell development is very complicated. In order to properly regulate just one gene expression of a single-cell layered gut of the sea urchin larva, at least 14 proteins binding the DNA at 50 sites are needed, Calestani said.

"Multiply that hundreds of times and you begin to understand the level of complexity involved in human development," she added.

Using a "simple" creature like the sea urchin embryo to uncover the molecular basis underlying development offers several experimental advantages compared to the use of mice. Raising sea urchin embryos is easy and inexpensive. One female can provide up to 20 millions eggs. The embryos develop in just three days and are transparent. Also, single cells can be easily observed live in the embryos.

"If we know how these biological processes work, then we can begin to figure out how to intercede to repair and to heal," Calestani said. "It holds a lot of promise."

Calestani is continuing her work with sea urchins at UCF in Orlando by examining the development of pigment cells found in the marine creatures. Those cells also might provide some insight into human immunity to diseases.

Calestani, who teaches genetics at UCF, worked with Davidson at Caltech before arriving at UCF.

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