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Gastrulation of A Frog Embryo
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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 Vertebrate Squid
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).
2) Several other genes (sine oculus, eyes absent,daschund) play roles similar to pax6 in eye development - Loss-of-function results in loss of eyes - Ectopic expression induces ectopic eyes.
3) The regulatory relationships between eye determining genes are different in flies versus vertebrates.
Normal Fly head
Jesper Kronhamn, Erich Frei, Michael Daube, Renjie Jiao, Yandong Shi, Markus Noll, and Åsa Rasmuson-Lestander Headless flies produced by mutations in the paralogous Pax6 genes eyeless and twin of eyeless Development 2002 129: 1015-1026.
Fly Lacking eyeless Function
Evolutionary Conservation of Hox Expression Patterns
Inverted-brateHypothesis
Evolutionary Conservation of Neural Induction
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
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 Vertebrate Squid
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 it ate 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.