more about pigment cells

note: i wrote this post and then Blogger crashed Safari. it was a good post, so i'm going to try to reconstruct it, but... aaargh! *curses blogger*

The close interaction in the cuttlefish between pigmentation and neural activity may seem like something out of a sci-fi movie. It may surprise you to learn that even in vertebrates, pigment cells have close developmental ties to the cells that go on to form the central nervous system. At the end of neurulation, the embryo's outer sheet of cells, known as the ectoderm, has rolled itself up and divided into two components, the neural tube, and the true ectoderm. However, a small population of cells that originally lay at the boundary between these two populations is destined for something else. These are the neural crest cells, and they go on to form a wide array of tissues, from sensory neurons and associated glia, to cartilage, muscles and bone, part of the heart and adrenal gland, and - you guessed it - pigment cells, including melanocytes.

Now, humans can't change their skin color - much less its texture or patterning - at will, so it may sound strange that these pigment cells share such an intimate past with much of our peripheral nervous system. However, many vertebrate species possess at least rudimentary control over their pigment cells*. Zebrafish can squeeze or spread their black pigment cells depending on environmental cues, and of course, the chameleon can change colors to blend in with its surroundings. Camouflage is a very useful adaptation - it's hardly a surprise that many species have evolved camoflage that changes.

(*Check out that link - there's a great descriptor of the cuttlefish pigmentation organ, which differs from - and is likely more accurate than - the quick explanation in my last post. Evidently each cell has every different color inside, and they just squish the cell around in different ways to express different colors. Awesome!)

There's a lot of really interesting research into the genetics and development of pigmentation patterns. The Parichy lab here at UW is using several different species of Danio - close relatives of D. rerio, the developmental biologist's favorite little fish, to determine the genetic factors responsible for different pigment patterns in adult fish. Pigmentation patterns are so crucial to the survival of any species, it is easy to imagine that the genes causing the patterns would be frequent targets of selection - both natural and sexual.