lecture 10: evolutionary conservation of patterning systems
DESCRIPTION
Claw. Eye. LECTURE 10: Evolutionary conservation of patterning systems. 2nd Axis. Evolutionary Conservation of Hox Expression Patterns. Evolutionary Conservation of Neural Induction. Inverted-brate Hypothesis. Dpp. dpp. msh. ind. vnd. Dorsal. BMPs. Msx. Gsh. Nkx2.2. - PowerPoint PPT PresentationTRANSCRIPT
Eye
Claw
2nd Axis
Evolutionary Conservation of Hox Expression Patterns
Inverted-brateHypothesis
Evolutionary Conservation of Neural Induction
Drosophila Neuroectoderm
Mouse Neural Tube
Sonic Hh
BMPsMsx Nkx2.2Gsh
Dorsal
Dpp
indmsh
vnd
dpp
Patterning the Neuroectoderm in Flies and Mice
A P/
Hh
Dpp
Hh Hh
BMP-4
A P
Fly wing disc
A/PAxis
Vertebrate Limb Bud
D/VAxis
P/DAxis
D
V
A P
NotchSignaling A P
DV
NotchSignaling
D
V
A P
Distalless
A P
DV
Distalless
Fly Eye
A P
Specification of theeye disc in the embryo
>1,000-X growth
eyeless: A master eye gene?
Eye Primordium20-40 Cells
Furrow
A P
Growth and patterning ofeye imaginal disc in larvae
dpphh
Early Steps in Fly Eye Development
R8R7
Sequential formation ofphotoreceptor clusters
Furrow
R2R5
R3R4R8 R1
R6 R7
873 51
PhotoreceptorDevelopment
Fly Eye Development
Furrow
A P
Patterning of the eye imaginal disc
dpphh
OpticVesicle
Brain
Outgrowth of the optic vesicle
Iris Lens
Retina
Photoreceptors
Cornea
FullyformedeyeOptic Nerve
Future lens
Future retina
Brain
Connectionto brain
Induction of the lens by retina
Reciprocal lens to retina inductionFuture lens
Future retina
Induction of the cornea by lens
Future retina
Future Cornea
Future lens
Non-neural ectoderm
Neuroectoderm
Formation of the neural tube
Neural Tube Epidermis
Formation of the Vertebrate Eye
Opticnerves
Lens
Photoreceptors
Epidermis
Invaginating eyeimaginal disc
Eyedisc
Morphogenetic furrow
Ant. Post.
873 51
PhotoreceptorDevelopment
Photoreceptorsinduce lens cells
Furrow
OpticVesicle
Brain
Lens
Retina
Cornea
Opticnerve
Photoreceptors
Iris
Future lens
Future retina
Brain
Future lens
Futureretina
Iris
Lens
Retina
Cornea
Opticnerve
Photoreceptors
Iris fold
Lens
Cornealfold
Lens fold
Eye primordium
Migrating lens cells
Future Retina
Comparative Eye DevelopmentFly Vertebra
teSquid
Is Eyeless/Pax6 a Master Gene for Eye Development?
Arguments in Favor:
Wild-type Wing
1) Decreased activity of pax6 genes results in reduced eye size in flies, mice, and humans.
2) pax6 genes are expressed in the early eye primordia of flies, humans, and squid, in which eyes were thought to have evolved independently.
Wing Mis-expressing Human pax6 gene
Eye
3) Mis-expression of fly or human pax6 genes in certain fly tissues (e.g. wing) result in formation of ectopic eyes.
Is Eyeless/Pax6 a Master Gene for Eye Development?
Arguments Against:1) Elimination of eyeless or pax6 gene function results in loss of more
brain structures than eyes (e.g. completely headless flies).
3) Several other genes (sine oculus, eyes absent,daschund) play roles similar to pax6 in eye development.
4) The regulatory relationships between eye determining genes are different in flies versus vertebrates.
Normal Fly head
Kronhamn et al., Development 2002 129: 1015-1026.
Fly Lacking eyeless Function
2) eyeless expression only induces eyes in certain tissues (e.g., wing).
Hox genes
A/P Axis
AbdomenHead
Tail
Mouth
Anus/Genitals
Sog/Chd
Dpp/BMP4
Neural Ectoderm
Non-neural Ectoderm
D/V Axis
Photosensitiveorgans
SensoryAppendages?
Eyespot?
Gills?
Protrusions orappendages
Reconstructing the Common Ancestor of Flies and Humans
What Was So Great About Our the Common Ancestor?
1) The common ancestor of humans and flies must have lived in a complex eco-system with many other species, some of which ate it and others of which it ate.
2) The creature and its decedents somehow displaced all other animal forms.
3) Why?? What was so great about this animal??
Possible Answers:
The Question:
1) The ancestor evolved a mechanism for extracting low levels of oxygen from the atmosphere and delivering them to internal tissues.
2) The ancestor evolved HOX genes, which allowed for the subsequent diversification of individual body parts.