Six developmental stages of a tardigrade embryo, from the four-cell stage (top left) to the 60-cell stage (bottom right). During these stages, cells may be competing to become the immortal germ cells. [Image 1 of 2 related images. See Image 2.]
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Bob Goldstein, an associate professor of biology in the College of Arts and Sciences at the University of North Carolina at Chapel Hill, and his lab are one of the few groups of scientists who study the evolutionary development in tardigrades microbes.
Goldstein uses microscopes that can record multiple optical planes over time to create videos of tardigrade embryos developing. "You can play back these films and see cells dividing on one side of the embryo and cells dividing on the other side," he says. "And from that, you can reconstruct cell lineages. You can watch from the one-cell stage as it divides to two cells, and then four and so on. And you can figure out the relationships between the cells, which can be important for just broadly understanding how development works."
Goldstein and Jenny Tenlen, a postdoc in his lab, are looking closely at germ cells in tardigrade embryos. Germ cells, which are made by all sexually reproducing animals, are sex cells. As an embryo develops, it sets aside once cell to become a germ cell, and this cell will eventually become either an egg or a sperm. It's the germ cell's DNA that is passed on when an organism reproduces. But we don't really know a lot about how organisms single out a specific embryonic cell to become the germ cell.
Goldstein and Tenlen think that in the tardigrade, two embryonic cells may compete for the honor. If that turns out to be true, and if Goldstein and Tenlen can figure out exactly how and why it happens, they may have taken a step toward figuring out how development influences evolution.
Goldstein's tardigrade research is supported by the National Science Foundation (grant IOS 02-35658).
Read more about Goldstein's tardigrade research in UNC-Chapel Hill's Endeavors magazine story Tardi-whats? (Date image taken: 2008; date originally posted to NSF Multimedia Gallery: Sept. 21, 2017)