MAKING EYES IN MICE AND MEN

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LECTURE 11 MAKING EYES IN MICE AND MEN
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Gastrulation of A Frog Embryo
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Formation of the Vertebrate Eye
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Comparative Eye Development
Fly
Vertebrate
Squid
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Is Eyeless/Pax6 a Master Gene for Eye Development?
Arguments in Favor

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.
3) Mis-expression of fly or human pax6 genes in
certain fly tissues (e.g. wing) result in
formation of ectopic eyes.
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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.
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Evolutionary Conservation of Hox Expression
Patterns
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Evolutionary Conservation of Neural Induction
Inverted-brate Hypothesis
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Comparative Eye Development
Fly
Vertebrate
Squid
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Reconstructing the Common Ancestor of Flies and
Humans
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What Was So Great About Our the Common Ancestor?
The Question

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

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.