This survey is designed to portray in graphic terms the ubiquity and diversity of the homeotic developmental genes across plants animals and fungi. It is based principally on ky illustrations and reference articles.
Homeobox genes and the vertebrate body plan E De Robertis, G Oliver, V Wright Scientific American Jul 90
The molecular architects of body design William McGinnis and Michael Kuziora Scientific American Feb 94
Homeobox Harvest Scientific American June 91
Homeotic genes are a ubiquitous feature of multi-cellular animals and fungi. Knotted maize mutants have a mutation in a homeobox gene regulating differentiation. Since then similar homeobox genes have been found in tomatoes and rice. This takes the first origin of the homeotic differentiation genes back to a billion years ago when the first multi-cellular organisms evolved.
Despite the obvious differences between the insect compound and vertebrate camera eyes, their homeotic genes have been shown to elicit comparable differentiation, especially segmentation, also have strong sequence similarity for eye differentiation. Here a mammalian regulatory gene, pax6 is able to elicit ectopic eyes on the leg of a fruit fly, showing the genes even have comparable action. From Climbing Mount Improbable by Richard Dawkins.
Amino acid sequences of the homeoboxes of three Drosophila melanogaster (fruit-fly) genes antennapedia, fushi tarazu, and ultrabiothorax are compared with a frog homeotic sequence. The strong conservation of the constatnt regions in the distantly-related frog is emphasized in colour.
Darnell, Lodish and Baltimore 1986 Molecular Cell Biology Scientific American Books.
The common nature of homeotic genes between such widely spaced phylla suggests evolution had to find a common scheme of embyogenesis in the pre-Cambrian before the metazoa evolved. A similar identity pertains between decapentaplegic in the fly and Bmp-4 in the frog. Both are equally effective in either species, except their effect have inverted in a way which reflects the proterostome/deuterostome inversion (New Scientist 18 Oct 1997 30).
Men-only gene may be universal. New Scientsit 14 Feb 98
Despite the great variety of mechanisms for determining sex, from XY, through ZW in mammals and birds, to haploid-diploid in insects such as bees, to temperature (turtles and alligators) to dominance (certain fish) there may nevertheless be a universal genetic switch similar to the homeotice developmental genes.
THE genetic machinery that determines an animal's sex may have at least one common feature in every animal after all, say researchers at the University of Minnesota. Until now, biologists had been puzzled to find that different genetic switches separated males from females on different branches of the tree of animal Iffe. But In this week's Nature (vol 391, p 691), a team led by David Zarkower reports that a gene called doublesex In fruit flies resembles a male-determining pne called mab-3 in the roundworm CaCaenorhabditis elegans. The two genes are so similar that proteins made by doublesex function normally in worms. Humans may share the gene. When the researchers searched a database of human gene sequences, they found a similar gene that Is active only in testis tissue. Bob Holmes