Why sea urchins are cool « Logan Science Journalism Program

Why study sea urchins, not mice, fruit flies or just something that doesn't look and feel so much like a wet pincushion? Our instructors David Burgess and Brad Shuster, two cell biologists, explained why these sea marine creatures can outshine other well studied favorites, technically known as model organisms, in the lab.
Turns out, you can get millions of urchin eggs and sperm quickly and easily, fertilize them all at once and they will develop simultaneously. These massive cultures of synchronized cells are important for biologists studying cell division or development because they can produce large enough quantities of the proteins or other substance being studied.
By comparison, at most you can squeeze about two dozen eggs from a single mouse with her hormones amped up.
Besides being plentiful, sea urchin babies develop quickly. The first cell division happens after about 70 or 80 minutes after fertilization, while for humans, the fertilized egg doesn't become two separate cells for 18 to 24 hours. And, for obvious other reasons, human embryos aren't good for research.
Plus, you have more in common with these tiny, spiny guys than you think.
Like the cells of a human embryo, sea urchin embryos divide themselves into three primary layers, the ectoderm, the future skin, brain and nerves; the mesoderm, mucsles skeleton, and parts of other internal organs; and the endoderm, which becomes the gut.
They are tough – in an experiment by Burgess and two colleagues sea urchin eggs placed in tiny, oddly shaped chambers (triangles, cubes, L-shaped) managed to locate their nuclei right in the centers, just as they would in their natural spherical.
"The thing about sea urchin eggs is they can take an unbelievable amount of abuse and they will still try to divide," explained Shuster.
Biologists like he and Burgess have unlocked, and are unlocking, a number of important secrets to reproduction, development and cell biology through these marine animals.
By studying sea urchin sperm fertilizing sea urchin eggs, others have been able to answer a fundamental question about how an egg prevents more than one sperm from fusing with it.
"The goal is to only have one," Shuster said. "How does nature say keep the extra sperm out? That's a problem for every organism."
The arrival of multiple of sperm would be the end of a potential embryo, which would end up with too much genetic material to continue developing.
By studying sea urchins, scientists discovered a two-part process that blocks late comers. First, after the one sperm enters, the egg's membrane changes its electrical characteristics for about 45 seconds – and it becomes just too shocking for another sperm to get it. The second block, the slow one, begins calcium is released just inside the cell, this causes vesicles – little bubbles inside the cell – to release their contents, which make the coating of the egg impermeable to late arriving sperm and forms a protective covering around the egg.
Research on sea urchin sperm has also explained how the molecular motors that allow them to swim work, according to Burgess, and the list goes on.
Sea urchins have also helped biologists understand how groups of genes interact to control the timing and location of development of particular structures, like the gut, through proteins called transcription factors. And developing sea urchins embryos are also helpful for studying the processes behind metatisis, by which cells leave their neighborhood and crawl to a new site. This is how cancer spreads.
Next, we'll see these critters in action. Tags: development, fertilization, model organism, sea urchins This entry was posted on May 20, 2011 at 4:04 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.