March 15 th , 2010 - Lab Meeting midline cell fate

March 15th, 2010 - Lab Meetingmidline cell fate

Outline

1. Hh and its role in midline cell fatea. MGb. Neurons

2. Wg and its potential role (or lack thereof) in midline cell fate

hh activates PMG specific gene expression patterns

WT UAS-hh hh[AC]

hh activate midline En in Tribolium

hh represses AMG specific gene expression patterns

WT UAS-hh hh[AC]

What might be happening?

1. hh from row G, H and the lateral CNS activate en expression in rows G?, H, A, B

2. From rows G-B, the MP4-6, MNB, and PMG arise

3. En in PMG represses AMG gene expression and promotes PMG gene expression

HhHhHh Hh

Hh

en expression

What might be happening?

1. Runt represses en expression and keeps it out of rows C-E

Does Hh direct gene expression in row F, or even more anterior? What about neurons?

HhHhHh Hh

Hh

en expression

RuntRunt

hh effects MP3 formation/fate

TupElavGFP

pleGFP

hh[AC]

hh[AC]

WT

WT

ptc GFP

What kind of cells are made in hh mutants?

The simplest explanation is that there are 4 neurons, 2 MP1 and 2 MP4/5.(Cas is also on in lots of MG, so Cas may be effected in a more complex way)

Conclusion: the effect of hh extends past the En+ cells

Cas Elav GFP Runt GFP En GFP

Outline

1. Hh and its role in midline cell fatea. MGb. Neurons

2. Wg and its potential role (or lack thereof) in midline cell fate

Reasons to think that wg is involved in midline cell fate acquisition

1. Its wg, it is involved in lots of cell patterning and cell fatea. pubmed search for ‘wingless signaling’ yields 980 papers and 164 reviewsb. ‘wnt signaling’ yields 7,848 papers and 1,493 reviews

2. During segmentation, wg is in a regulatory loop with en and hh to producing a signaling center

wg

en

hh

ptc

Reasons to think that wg is involved in midline cell fate acquisition

3. wg function regulates anterior cell fates in the epidermis and lateral CNSa. in wg mutants, naked cuticle (anterior epidermal cell fate) is lost

b. in wg mutants, NB4-2 (anterior cell) cell fate is lost

Reasons to think that wg is involved in midline cell fate acquisition

4. wg is expressed in the midline cells early in their development

stage 8

stage 10 stage 12stage 11

stage 9

wgEn

Reasons to think that wg is involved in midline cell fate acquisition

5. Ectopic wg and wg mutants show alterations in l(1)sc expression

Bossing and Brand, 2006

stage 10

Reasons to think that wg is NOT involved in midline cell fate acquisition

1. misexpression of wg in the midline has no effect on Runt/En/morphology

Bossing and Brand, 2006:The earliest time we can express Wingless in all midline cells is stage 10. At this stage, ectopic Wingless no longer interferes with midline cell differentiation.

RuntEnGFP

stage 11 stage 15

Reasons to think that wg is NOT involved in midline cell fate acquisition

2. misexpression of Wg downstream effectors in the midline has no effect on Runt/En/morphology

Runt En GFP

stage 11 stage 15UAS-arm[s10] UAS-tcfΔN

stage 11 stage 13

Reasons to think that wg is NOT involved in midline cell fate acquisition

3. wg mutants still show Runt+ Sim+ cells and En+ posterior cells

wg[1-12]

Sim Runt

wtstage 13stage 13

En GFP

Reasons to think that wg is NOT involved in midline cell fate acquisition

4. Ectopic wg and wg mutants show alterations in l(1)sc expression….but we dont

Bossing and Brand, 2006

stage 10know what is being assayed.

where is the midline?

can wg turn off l’sc in non-midline cells, it looks like it. Is this then related to segmentation?

Reasons to think that wg is NOT involved in midline cell fate acquisition

5. In wg mutants ‘early’ en is absent, but ‘late’ en is not effected

Bossing and Brand, 2006

Loss of ‘early’ En is likely due to a loss of the regulatory loopwgenhhwg

the presence of en seems due to the fact that wg is not regulating midline gene expression

So, what do I think

wg is probably NOT involved in midline cell cell fate/ differentiation

So, what do I think

Epidermal patterning and segmentation:1. There is an early role for wg in establishing en and hh expression in the posterior

of the segment

2. wg regulates anterior cell fate by repressing the expression of genes that in the wg mutant are activated ectopically in the anterior.

3. l(1)sc is expressed in the anterior of the segment due to segmentation genes (which ones I don’t know).

l(1)sc wg En/hh

So, what do I think

Midline cell patterning and cell fate:1. Misexpression of wg or downstream components does not alter midline cell fate

whereas hh and ci can. So, wg regulation of l’sc is probably not occurring at the same time as hh regulation (probably earlier, during segmentation).

2. The presence of late en and absence of early en is good proof that wg plays no role in hh regulation of en (and probably l’sc).

3. This likely means that wg repression of gene expression in the anterior of the segment is not present. This might allow hh signaling to effect gene expression in anterior cells (ie MP1, MP3), which it does in MP3.

4. Something makes the midline cells different from lateral CNS and epidermis, a good candidate is single-minded. How does it do this?

How can one nail down the role of wg?

1. reporters of wg activitya. Top-Flash (not tried in flies, just s2 cells, works in mice)b. nkd-GFP

2. verify the expression of en and l’sc in wg mutants. If they are present in the expected cells than wg plays no role.

What might be happening?

3. Runt in Row C, D, E opposes Hh activity and keeps en expression off.

Evidence comes from Josephs work on Runt and En cross-repression

HhHh Hh

Hh

HhHh

en expression

Runt

What might be happening?

4. MP1 arises from Rows C, D, E (Runt+ cells).

5. odd expression in Rows A and B is unrelated to MP1 , odd expression is intiated de novo in MP1

HhHh Hh

Hh

HhHh

en expression

Runt

MP1

What might be happening?

6. MP3 arises from row F7. MP4-MNB and PMG arise from rows G-B8. AMG arise from rows C-F

HhHh Hh

Hh

HhHh

en expression

Runt

MP1 MP3

MP4

MP5

MP6

MNB