Delta Signaling From the Germ Line Controls the Proliferation and by shuifanglj

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									Delta Signaling From the Germ Line
    Controls the Proliferation and
Differentiation of the Somatic Follicle
 Cells During Drosophila oogenesis


    Genes & Development 15:1393

           Alexa Alexander
Generalized Oogenesis




(Campbell 4th edition)
      Oogenesis




(Van Eaden & St. Johnston, 1999)
              Egg anatomy


                            Stalk cells
    Nurse      Oocyte
                              Polar cells
    Cells




Epithelial Follicle Cells
  Polarization
• Grk/Top oocyte
  nucleus to follicle
  cells (Egfr)
• Signal returned
• Microtubule array
• Gradient for
  Bcd/Osk
• Why can polar cells
  do this when other
  cells can’t?

             (Gonzalez-Reyes et al., 1995)
         The Notch Pathway

• Notch is a transmembrane receptor for
  ligands Delta, Serrate and related
  orthologs (DSL)
• DSLs are transmembrane proteins with
  large extracellular domains
• Ligand binding causes Notch receptor
  to undergo proteolytic cleavage
  (releasing intracellular domain)
          Materials and Methods

•   Confocal microscopy (laser)
•   Fluorescent proteins e.g. GFP
•   Labelled different gene products
•   Examined oocyte development
Observation 1: Notch mutants do not
      adopt a polar cell fate.
            Presence of FAS III (red)

               wildtype          Notch mutant

   Early in
 development




    Later
 Observation 2: Notch is required for
differentiation of polar and stalk cells.
     Presence of A101 enhancer-trap line (blue)


                 Wildtype          Notch mutant


  Late in
development
      Observation 3: Notch is required for
      the epithelial follicle cells to exit the
               mitotic cell cycle.
Presence of FAS III (red)

              Notch Mutant   Epithelial follicle cells don’t
                                  become polyploid
    Early in
  development

                                   Notch Mutant


      Later
     Observation 4: Other mutations give
      rise to the same Notch phenotype.
1.) Nucleus signals Notch           2.) Cleavage to Presenilin
                       Notch        Causes translocation of Notch
                      Receptor
                 1
                                           2

Oocyte            3
Nucleus                                               Follicle Cell


    3.) Translocated Notch interacts with Su(H) protein
    Together these regulate other target genes
    Can be competitively inhibited by Hairless
     Observation 5: Delta activity is
       required in the germ line.
                        Epithelial follicle cells with
                        null Delta = no effect
Loss of Delta in
the germ line creates
severe fusion of
egg chambers
                            Delta most abundant
                            in nurse cells and oocyte
Delta
activity
continued…

Delta activity first
required in germarium
for separation of egg
chambers
            Delta activity continued…
Epithelia cells lack fringe and only
respond to Delta at high concentrations
ie: later in oogenesis




Stalk and polar cells
express fringe
a glucosyltransferase
that increases Notch’s
sensitivity to Delta
              Discussion
• Notch in oogenesis promotes follicle
  differentiation
• Germ line critical to follicle development
• Gurken/DER complemented by
  Delta/Notch pathway
• Gurken is spatial control and
  Delta/Notch is temporal control

								
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