DB Result and Conclusion 2

Sea Shells: Can explain by 3 input variables

Simple changes --> Various outputs

Fern Leaf: Can explain by internode ratio formula

Same algorithm used at 3 diff. scales

Frog Embryo: Early identity changes; later cell moves back

s-->p mechanism at later stages

Chick Embryo: Transplanted cells make a toe!

Leg & wing use same coordinate system

Planarian: Morphallactic regulation, normal polarity

Wolpert-style Gradient

Planarian: Regulation with variable polarities

Not enough time to overcome "noise"

Planarian: Regulation with normal polarity

Gradient has "noisy" imperfections

Planarian: Reversal of axial polarity

Morphogen could be simple molecule

Hydra: Morphallactic regulation, normal polarity

Disproves idea of morphogen pumping

Hydra: Frequency of heads = highest from the neck

Gradient of "head activator" exists

Hydra: Frequency of heads = highest near the foot

Gradient of "head inhibitor" exists

Hydra (Observation): Activator gradient has higher slope

Turing's Reaction-Diffusion Model

Frog retina: Can make a map where tectal cells fire

Sperry's Neurospecifity Hypothesis

Frog retina: Cells stick to the "correct" half of tectum

This result supports Sperry's Hypothesis

Frog retina: AP & DV axes get inverted at diff. times

X & Y axes get specified at diff. times

Fruit fly (Drosophila): Causes various types of mutant defects

Assess how genes control development

Fruit fly (Bithorax): Homeosis of body segments

Anatomy is specified by a binary code

Fruit fly (Antennapedia): 1:1 correspondence of leg & antennal regions

Organs differ in "interpretation mode"

Fruit fly (extra-sex-combs): Null mutation transforms all segments to A8

Gradient uses repressor, not activator

Fruit fly (patched & spiny legs): Causes "segment polarity" inversions in larva

Duplicates if remove >1/2 of clockface

Fruit fly (branched legs): A curved zone of cell death exists in mutant

Does the cell death cause triplication?

Fruit fly (branched legs): Causes same triplications as in the mutant

Cell death region triggers extra organs

Fruit fly (branched legs): Clones arise in new branches more than stem

Cell death region triggers extra organs

Fruit fly imaginal discs: Each piece makes specific part of wing

Shows that cell fates are already fixed

Fruit fly imaginal discs: 3/4 pieces regenerate; 1/4 pieces duplicate

Led to the Polar Coordinate Model

Fruit fly imaginal discs: They don't. One leg 1/4 piece regenerates

Angular coordinates are crowded in 1/4

Salamander (Blastema): Two extra arms = "supernumeraries"

Consistent with Polar Coordinate Model

Salamander (Limb bud): Two extra arms = "supernumeraries"

Consistent with Polar Coordinate Model

Chick wing bud: Proximal bones develop before distal ones

Led to the Progress Zone Model

Chick wing bud: Mirror-image duplication (Posterior -> Anterior)

Led to the ZPA Model

Chick wing bud: Mirror-image duplication (Anterior -> Posterior)

Argued against ZPA Model