Neurulation

(see slides posted at end of DB5 ppt)

Inducer Responder

SignalingInducer Responder

Signals can actin a graded fashion

Setting up a signaling gradient:

the role of the wingless gene

Cells know theirpositions within the body anddifferentiateaccordingly

Anterior

Posterior

A- HairP- Bare Skin

segment

wild type

A = hair

P = bare skin

To set up this pattern, flies use the secreted protein Wingless to specify a posterior fate

segment

BePosterior!

Cells instruct one anothervia cell-cell signaling pathways

BePosterior!

Cell-cell signaling can be influenced by distance between cells

Yes Ma'am!

Pardon me?

Anterior: Low Wingless,Hairs

Posterior: High Wingless,Naked Cuticle

Wingless-expressing cellsWingless diffusesaway from the cellsthat secrete it

Wingless signaling specifies posterior cell fates in the ventral epidermis

arm mutantwild typeALL cells have anterior (hair) fate

A = hair

P = bare skin

Therefore, all cells can see wingless, and the concentration of wingless itself is what determines cell fate

Setting up a signal gradient

Turn on new genes!

Yes Ma'am!

Cell surface

Nucleus

Signal transduction moves information

from the cell surface to the nucleus and

other cellular targets

Turn on new genes; pass it on

Yes Ma'am!

Cell surface

Nucleus

Turn on new genes; pass it on Turn on

new genes; pass it on

Turn on new genes; pass it on

Signal transduction occurs through a series of steps

Geneticsrevealed theligand andproteins inthis signal

transductionpathway

Genetics can also position proteins within the signaling pathway

An example of the conservation of

key developmentalregulatory machinery

across animal phyla

flies mammalsSee Figure 3.28

Colon cancer, the second leading cause of cancer deaths in the U.S.,

results from inappropriate Wnt signaling

Polyps, the first stageIn tumor development

Insects:

A model systemto study hormonalcontrol ofpostembryonic development

Figure 15.9

Long range signaling

Vincent B. Wigglesworth

Discovered that blood-borne hormones control insect metamorphosis through experiments with a blood-sucking bug, Rhodnius prolixus

Blood-bornehormonesregulatethe timing ofmetamorphosis

Experiment #1

induces 1st instar larva to molt into very small adult

Experiment #2

Other hormones prevent metamorphosis

Experiment #3

Other hormones prevent metamorphosis

Transplant corpus allatum from 4th to 5th instar larva

Result: blocks metamorphosis, instead get “6th instar larva”

Adult

The cascade of hormonesregulating insectmetamophosis

Figure 15.16

PTTH

20E

Steroid hormones (ie 20E):hydrophobic signaling molecules

that can pass through the plasma membrane

20E

Figure 15.16

Most signals

Steroid hormones

(ie. 20E)

An insecticide produced by plants cause premature metamorphosis