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LECTURE 10: Evolutionary conservation of patterning systems

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.

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LECTURE 10: Evolutionary conservation of patterning systems

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  1. Claw Eye LECTURE 10: Evolutionary conservation of patterning systems 2nd Axis

  2. Evolutionary Conservation of Hox Expression Patterns

  3. Evolutionary Conservation of Neural Induction Inverted-brate Hypothesis

  4. Dpp dpp msh ind vnd Dorsal BMPs Msx Gsh Nkx2.2 Mouse Neural Tube Sonic Hh Patterning the Neuroectoderm in Flies and Mice DrosophilaNeuroectoderm

  5. Fly Eye

  6. Growth and patterning of eye imaginal disc in larvae >1,000-X growth Furrow dpp A P hh Early Steps in Fly Eye Development Specification of the eye disc in the embryo eyeless: A master eye gene? A P Eye Primordium 20-40 Cells

  7. Sequential formation of photoreceptor clusters Furrow Photoreceptor Development R 2 R 3 R 1 R 8 R 7 R 5 R 4 R 6 R 8 R 7 1 3 5 7 8 Fly Eye Development Patterning of the eye imaginal disc Furrow dpp A P hh

  8. Formation of the Vertebrate Eye

  9. Comparative Eye Development Fly Vertebrate Squid

  10. Eye Wild-type Wing Wing Mis-expressing Human pax6 gene Is Eyeless/Pax6 a Master Gene for Eye Development? Arguments in Favor: 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.

  11. Kronhamn et al., Development 2002 129: 1015-1026. Normal Fly head Fly Lacking eyeless Function Is Eyeless/Pax6 a Master Gene for Eye Development? Arguments Against: Elimination of eyeless or pax6 gene function results in loss of more brain structures than eyes (e.g. completely headless flies). 2) eyeless expression only induces eyes in certain tissues (e.g., wing). 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.

  12. Eyespot? Sensory Appendages? Head Abdomen Tail Anus/ Genitals Mouth Gills? A/P Axis D/V Axis Dpp/BMP4 Non-neural Ectoderm Photosensitive Protrusions or Neural Ectoderm Hox genes Sog/Chd organs appendages Reconstructing the Common Ancestor of Flies and Humans

  13. What Was So Great About Our the Common Ancestor? The Question: 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 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.

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