DEVELOPMENTAL BIOLOGY:
Possible New Roles for HOX Genes
Steven Dickman
MADRID, SPAIN--At a workshop on development and evolution held here last month by the Madrid-based Juan March Foundation, researchers reported finding a putative second cluster of HOX-like genes in Amphioxus, a fishlike marine invertebrate that is seen as a crucial evolutionary link to vertebrates. A great deal of evidence has shown that the HOX genes play important roles in laying down the head-to-tail patterns of embryos of many different organisms. The results are intriguing because, in addition to shedding light on Amphioxus development, they may also help explain a key change leading to the rise of complex organisms during evolution: the creation of multiple "germ layers"--the primitive embryonic tissues that produce all of a creature's tissues and organs. While previous HOX genes are expressed in the outermost layer, the ectoderm, the researchers found that the HOX-like genes in the new "sister cluster" are expressed in the innermost layer, the endoderm. The results therefore suggest that the appearance of the new cluster is related to the creation of the endoderm.
