Hedgehog Expression
description
Transcript of Hedgehog Expression
Hedgehog Expression
Hedgehog– Expression in posterior of segment (s6-11)– Wheeler: stage 9 in posterior of segment; very weak (or absent) at stages 10-11 in midline
but present adjacent to midline– Bossing protein in midline until s10 then in ectoderm until 11
s11
s10
Patched Expression
Patched or Ptc-lacZ– Present in l(1)sc+ En+ cells at stage 10
Is ptc adjacent to or includes hh+ cells? When does ptc first appear? Is ptc present in hh mutants?
Hedgehog Mutants
hh mutant (Bossing)– l(1)sc absent
» all (?)
– early en (s9) ok– Late en absent
– sim expression reduced
– ts: hh functions at s10-12– Some midline cells die by stage 17
Hedgehog Mutant
hh mutant (Klämbt)– Increase in AMG (extra MG) at expense of neurons– Conc.: PMG → AMG, effects midline neuron development
AA142: wild-type
AA142: hh (increase in AMG)Reduced X55: (PMG?)
AA142: ptc (reduced AMG)High X55: (PMG?)
Hedgehog Misexpression and Transplantation
hh misexpression (sim-Gal4 UAS-hh)– Induces l(1)sc and en expression in all midline cells
– Anterior commissure absent; posterior commissure present
– Odd+ MP1s are absent and MG disrupted (?)
Lethal(1) Scute
l(1)sc expression– Overlaps En+ cells
l(1)sc mutant– En expression reduced
(similar to hh)
l(1)sc misexpression– No effect on en expression
Engrailed Misexpression
en misexpression– Reduction in MP1s and MG– MG differentiation affected– Eliminates anterior commissure– Similar to hh function– Posterior neurons relatively
present and relatively normal
Model
Model– hh subdivides segment into anterior and posterior compartments– In posterior: hh activates l(1)sc expression (release of Ci76) then en (via l(1)sc or Ci-long)– l(1)sc and En are required for formation of VUMs and MNB– lack of hh signaling in anterior gives rise to MP1s and AMG
lack of hh signaling results in MP1 group Presence of hh signaling results in MP4 group MP3 group? (wingless?)
Wingless Expression
wg misexpression (Bossing; Wheeler)– wg expressed anterior to En+ and hh+ cells– On at stage 10, later (?)
wg s10
Wingless Mutant
wg mutant (Bossing)– Increase l(1)sc cells from 6 → 10– Reduction to 3-5 En+ cells (only early En, not later
En)
wg mutant (Klämbt)– Increased AA142+ MG 3 → 10 cells– Neuronal markers may also be present (mixed
cells)
Wingless Misexpression and Transplantation
wg transplantation– Inhibits l(1)sc expression
wg misexpression– No affect on en expression– No affect on axon scaffold
Wingless Model
wg maintains early en expression wg inhibits anterior spread of hh signaling Inhibits l(1)sc and early en+ cells anterior cells Predict that wg mutant would result in fewer AA142+ cells, but instead they increase
– Maybe loss of early En results in more anterior fates that cause formation of more AMG
How do Notch, Sim, Egfr, Vein, Spitz fit?
Vein Expression
vein expression– All midline cells from stages 7-10– Stage 11: subset (AMG?)– Stage 12: off
s6 s10 s11
Vein Mutants
vein mutant– wt: st11: 6 AA142+ cells; st17: 3 AA142+ cells– vein: st 12: 3 AA142+ cells; st17: 3 AA142+ cells– vein: early role in generating AMG– st17: axon scaffold normal; disorganized earlier
s12
s17
wt vn
Spitz-Vein Double Mutants
vein and spi single mutants– No effect on ventral-most midline cells (neurons)– spi vn double mutant: strong reduction in neurons
» More severe scaffold defects– vn expression requires spi
vn spi/+
s16 anti-Sim
wt
spi
vn spi
Midline Glia Pro-apoptotic Genes
Expression– hid expression high in AMG, PMG(?)– rpr expression transient; detected in small # cells, AMG or PMG (?)– grim expression (?)
Genetics– slit-lacZ s16
» wt: 3 MG» hid mutant: 6 MG (AMG, no PMG)
• spi activation results in phosphorylation of hid and inhibition of apoptosis» H99 (hid- rpr- grim-): 10 MG (AMG + PMG); grim and rpr required for PMG» X25 (hid- grim-): 8 MG (AMG + 1-2 PMG)» Model: hid (AMG); grim + rpr (PMG)