Extraordinary Embryo of the Week

Oops, a day late again. I was shopping yesterday. I'm sure all 2 of my readers understand that me getting a bargain price on some beautiful black patent leather pumps is worth a slightly late blog post :D

Anyway:



This little guy is a Xenopus laevis embryo that I stained for the expression of a gene called FGF-8 (fibroblast growth factor 8).

FGF-8 is important for the development of many different tissues throughout the body - you can see at this stage that FGF-8 is turned on in the tail bud (to the right of the picture), the somites (the stripy bits along its middle), the midbrain-hindbrain boundary (the stripe at the top of its head) and a couple of the branchial/pharyngeal arches (other stripy bits on its head).

So what?

This gene is being turned on in a bunch of different places. And in each different tissue, it is doing a slightly different job. How can the same gene have different functions in different places?

It all depends on context. The environment that the cells are in, and the complement of genes that are turned on in each cell, all affect how FGF-8 functions. It's kind of a space-saver in the genome; instead of having a different set of genes for every conceivable developmental job, we find that some genes are re-used all over the body to control the development of different organs and tissues, and FGF-8 is just one of these multifunctional genes.

FGF-8 does even more work during development at different developmental stages. For example, later on in development, FGF-8 will be used to control the growth of the developing limbs.

So, our Xenopus embryo above illustrates a couple of really fundamental ideas in developmental biology:

1. The same gene can perform different functions in various tissues (AND at different time-points).

2. The environment and genetic context affect how a gene will function.

I'd really like to pause here, and I'll pick up later this week to explore what these points mean for the evolution of developmental systems.