Creating a fly

• How to build a fly?

  1 subdivide embryo into anterior and posterior.

  2 define smaller segments. (thorax)

  3 assign identity to segments
• cytoplasmic determinants of anterior

  Bicoid maternal effect gene (head n thorax)
• cytoplasmic determinants of posterior axis

  Nanos maternal effect gene: (abdominal segments and posterior)
• Morphogens


  genes products that directly govern the proccess of tissue development during pattern formation
• Caudal protein 


  assist in defining the posterior end of embryo
• Bicoid represses translation of caudal protein by binding to elements in the 3'UTR of the caudal mRNA preventing the translation initiation complex proteins that bind to the m7G cap.

  
• Nanos represses Hunchback n does not act like a morphogen
• Maternal-effect genes assist in the sequential activation of

  gap genes

  pair rule genes

  segment polarity genes

  homeotic genes
• Maternal effect genes

  Anterior to posterior gradients
• Zygotic Gap genes

  divide embryo into broad regions
• Zygotic pair rule genes

  divide embryo into stripes about two segments wide

  defines segment borders
• Zygotic segment polarity genes

  divide segments into anterior and posterior halves
• Homeotic selector genes


  specify the identity of each segment
• Hunchback


  master gap gene

  controlled by bicoid

  together with bicoid control other gap genes
• Positional information and the French flag model (Wolpert, 1996)

  The expression of genes is either activated or repressed based on the concentration of another protein
• Kruppel

  specified by hunchback protein

  above a threshold krupple is repressed

  at lower concentration krupple is activated
• Transcription of the GAP gene Kruppel is inhibited by

  nanos and high concentrations of bicoid and hunchback.
• Gap genes


  respond to many genes and have multiple bonding sites in their promoters

  They regulate pair rule gene because the binding site cause repression and activation.
• Hox genes are transcription factors that regulate the expression of other genes


  on part of transcription factor is responsible for DNA binding

  middle dimerization

  surface-mactivation/ repression of genne
• Homeodomain


  a conserved 60 amino acid protein found in all HOX genes. n dna binding capacity
• hox genes and homeodomain

  conserved between different hox genes n species