Rapid test of embryo mechanics
Fig. 1: Life cycle of a typical sea urchin, Arbacia punctulata.


The goal for this project page is to devise a fast, cheap, and easy method to screen treatments (e.g. drugs, pollutants, other environmental conditions) to identify ones that have some mechanical effect on sea urchin embryos, before doing more difficult experiments to determine the nature of that mechanical effect.

See comment by MV for more on why this challenge project matters.
Although the focus is sea urchin embryos, people can participate in the project who do not have access to urchin embryos.

Some things that would help in devising this method include:

  • A design for a device to use in testing large numbers of embryos at once.
  • A physical implementation of the device.
  • Experimental validation of the device.
    • With inanimate objects (e.g. something like gelatin spheres)
    • With urchin (or other) embryos.
  • Theoretical analysis of device/method.

Why sea urchins: Sea urchin embryos are an important model system in developmental biology because they are relatively easy to get, culture, and do experiments with. What has been learned from sea urchin development has greatly helped researchers understand development and cell biology in other animals. Although the focus for this project page is developing a technique to be used with sea urchins, the technique could be applied to lots of small, soft spherical things (e.g. other round embryos, spherical cell aggregates, other organisms, such as Volvox, etc.).

About sea urchin embryos:

Some of the advantages of using sea urchin embryos for developmental biomechanics include their transparency, geometric simplicity and symmetry, and their physical sturdiness. These properties make mechanical analyses and experiments much easier in sea urchins than in other major model systems. In addition, one can get them in large numbers and culture them easily.

The sea urchin life cycle (Fig. 1) starts with a single cell, the egg. After fertilization, the egg divides multiple times to form a spherical shell of cells — one cell thick — around a cavity. At this point the cells in the layer (the epithelium) form cilia, and hatch out of the protective coat surrounding the embryo, to swim freely in the ocean. During this period —the blastula stage — they do not have neurons, muscles, or any differentiated tissues. They are just an (approximately) spherical ball of cells. Soon, cells leave the cell layer at one end of the embryo, and crawl inside the cavity (Fig. 2). Later in development, those cells will form the larval skeleton.

Fig. 2: Hatched blastula-stage embryo of the sand dollar1 Dendraster excentricus. This video was filmed at approximately real time. The embryo spins because the cells have beating cilia that make it swim. Normally it would also move forward rapidly (a few body lengths per second), but it was trapped to make the video. You can see the outer cellular layer (the epithelium), the blastocoel space inside, and the cells that have crawled inside the embryo (the mesenchyme cells) at one end of the embryo (the "vegetal" pole). The embryo was approximately 190 µm long. It was imaged by Mickey von Dassow using an Olympus BH2 microscope (40x objective, bright field), and a Lumenera microscope camera.

Because the embryo hatches as a blastula, there are no protective coats to remove, which is convenient for experiments; however, because they swim, they don't stay on the bottom of a dish, which makes some kinds of experiments more difficult.

After the blastula stage, one end of the embryo dimples inwards2. The dimple extends to meet the other side of the embryo, forming a tube. This tube becomes the larval gut. These and other processes transform the embryo into a larva, which looks a bit like Sputnik (Fig. 1). The juvenile sea urchin grows inside-out within the swimming, feeding larva3. Once it finds the right habitat, the larva undergoes the process of settlement and metamorphosis: the juvenile adheres to the sea floor, and turns right-side-out; and the larval structures are lost. The juvenile then grows up to be the adult sea urchin people are familiar with.

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