Wednesday, October 31, 2012

Danio rerio

What you see here on the cover of the 12 October issue of Science is obviously an embryo, at a rather advanced stage of development but still smaller than this letter o. But of what creature? A non-expert would be hard pressed to identify the species, or even the order. It is, in fact, a zebrafish, one of those model organisms researchers use to study the "miracle" of development.

How many cells? I don't know, but a rough calculation suggests about 10,000. A fertilized egg. Two. Four. Eight. Sixteen. Segments, cavities, appendages, folds. What will it be? A zebrafish? A hummingbird? A human?

I think of lines from a heartbreaking poem by my colleague Anna Ross, from her collection Hawk Weather. She describes, tenderly, lovingly, her own miscarried embryo: "Little yolk, fly-speck, web/ unworked, detail without name,/ unlatch yourself from me, go."

The special section in Science addresses what we know about the "forces" in development, but truth be told we don't know much about how information in that first fertilized cell, in interaction with the environment, signals the unfolding of an animal of a specific species. Segments, cavities, appendages, folds.

Fly-speck, zebrafish, you know your destiny. Two. Four. Eight. Sixteen. You will swim in the scientist's aquarium, flashing your blue stripes, glittering translucent. The researchers love you for the easy view of your glassy interior. They'll feed you food flakes and watch as you lay your hundreds of eggs every few days, so profligate you are, so extravagant with progeny, you swim with your sisters in a sea of embryos. They scoop up your offspring and watch, watch, as the flyspeck becomes a darting fish.

Will unraveling the mystery of development require a Newtonian Revolution in biology? Or is it only a matter of scrutinizing the unfolding embryo in ever more intimate detail, the "physico-genetic determinants"? Or both? Fly-speck, pinhead, peppercorn, pea. Segments, cavities, appendages, folds. Time will tell. "Go, almost thing,/ the sundews have opened/ their sticky pink mitts to catch/ your brothers…"