Homeobox Genes

• Von Baer, in early 19th century, observed all vertebrate look similar in early embryonic development stages, and Geoffroy Saint-Hilaire declared all animals have same body plan, because main nerve cord is in insect’s front part and in vetebrate’s back part, Saint-Hilaire hypothesised vertebrates were upside down invertebrates
• Many genetic breakthrough is from fruit flies as they reproduce rapidly (short life cycle), small/easy to breed, only has 4 chromosome and readily exhibits mutations (seen with light microscope)
• Fruit flies are highly specialised with 2 wings and 3 body segments, ancestors had 4 wings and many body segments; yet embryo starts with 16 equal segments (these then merge)
• 1940s: Edward B. Lewis studied homeotic genes and discovered single mutations causing body segment duplication and extra wing pairs, but affecting hundreds of genes in body shape (acting as master switches)
• 1970s: Fruit fly homeotic genes were sequenced, revealing 180-base DNA (homeobox) sequences that translate into 60 amino acid long proteins (homeodomain) that regulate cell fates, growth, and development (switch genes on/off, transcription factor)
• Hox Genes: Only in animals, control embryo development along head-tail axis (body parts placement), arranged in hox clusters with up to 10 genes; tetrapods have 4 clusters, flies have 1, they code for homeodomain proteins, triggering cascades of genes
• Hox Genes: Only in animals, control embryo development along head-tail axis (body parts placement), arranged in hox clusters with up to 10 genes; tetrapods have 4 clusters, flies have 1, they code for homeodomain proteins, triggering cascades of genes
• Homeotic Genes:

  • Large and ancient gene family involved in controlling anatomical organisms development (morphogenesis); ensure all structure in correct location according to body plan
  • Highly conserved through evolution, acting as molecular architects and direct body building according to definite detailed plans; so are very similar and function