VL: 13 Drosophila melanogaster- Cell polarity & Signal transduction

Question 1

Drosophila melanogaster
bristle

Answer 1

adult external sensory organs on the back
* massive screens were made to find genes that are important for cell fate
* Gene numb: because the muatnts were missing sensory neurons
* activation of numb via heatshock passible -> able to induce numb at any time

Question 2

Numb activation in different phases of cell devision

Answer 2

1) In first cell devision -> Phenotyp was balding
2) In second cell devision -> Twinning Phenotype (two hairs insted of one)
3) Without activation of numb-> just socket cells no hair

Numb defines particular cell fate in mitosis
-> assymetric cell devision
(Numb just on one pole of the cell, leading to the assymetric cell dev.)

Question 3

Asymmetric cell division-
Inscuteable (weiss nicht ob er das geskippt hat)

Answer 3

Numb -> asymmetric cell division in PNS and CNS.
Prespero -> TF required for correct cell fate specification and differentiation in PNS and CNS.

• Inscuteable is expressed in the cells which localize Numb and Prospero.
• In neuroblasts , Inscuteable is asymmetrically localized to the apical side, opposite to Numb and Prospero.
• inscuteable mutants are defective in the orientation of mitotic spinle and localization of Numb and Prospero.
• inscuteable controls asymmetric protein orientation during mitosis.

Question 4

Mammalian cell devision (Brain and skin)

Answer 4

Brain: Planar or apikal- basal assymetric devision -> gives rise to different cells.

Skin: on apical side -> new fate; on basal side normal devision

Question 5

Drosophila melanogaster germband extension

Answer 5

shortening in dorsal ventral achsis and elongation in anterior- posterior achsis.
coloured cells movement

Question 6

Segment polarity in Drosophila melanogaster development

Answer 6

Wingless (Wg) and hedgehog (Hh) feed back on each other; Wh also promotes expression of Engrailed (En) (Denticle belt and naked cutile abwechselnd)

In absence of Wg activity, expression of Hh and En is lost - leading to a loss of segment polarity and pattern (Naked cuticle absent)

Same happens, when Hh is repressed.

If Hh is misxpressed, producing a dulication of part of each denticle belt

Question 7

The Drosophila compound eye – another
model for studying molecular pathways

Answer 7

• 2 compound eyes
  ~800 ommatidia in regular pattern, image formation
• ommatidium:
  ~20 cells, with 8 photo
  receptor (R) cells in characteristic pattern
• Planar epithelial polarity within the
  Drosophila compound eye = “mirror line”, eye equator
• Drosophila eye is used as a model to study planar cell polarity -> very similr structures are found in mammals e.g. hair on leg of mouse and drosophila, orgenized in a unique streak (polarity proximal to distal)

Question 8

Frizzled mutations on hair growth

Answer 8

In frizzeld mutant-> misoriented hair

• Drosophila wing hair point distally in wild type animals but are misoriented in frizzled mutants.
• Hair on the mouse paw point away from the body in Frizzled6
  heterozygotes but display a characteristic swirlingpattern in Frizzled6 homozygotes.

Question 9

Roles of WNT signaling
Lecture: Signal transduction II
Wnt

Answer 9

Wnt signaling has roles in carcinogenesis and embryonic
development (body axis patterning , cell fate specification , cell
proliferation and cell migration)migration). These processes are necessary for proper formation of important tissues including bone, heart and muscle.

Wnt signaling also controls tissue regeneration in adult bone
marrow, skin and intestine