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Early Vertebrate Development

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Early Vertebrate Development. Early Development of Mammals Early Development of Birds…if we have time. Long and Winding Road…. Both Egg and Sperm have to overcome physical barriers. Ampulla - site of fertilization. Cleavage in Mammals. Rotational cleavage 1 st Meriodionally

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Early Vertebrate Development

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  1. Early Vertebrate Development • Early Development of Mammals • Early Development of Birds…if we have time.

  2. Long and Winding Road… • Both Egg and Sperm have to overcome physical barriers. • Ampulla- site of fertilization.

  3. Cleavage in Mammals • Rotational cleavage • 1stMeriodionally • 2nd one divides meriodionally, one divides equatorially • Asynchrony • No real Mid-Blastula Transition.

  4. Compaction • Division of early embryo up to 8 cell stage is loosely arranged. • At 8 cell stage, cells form tight interactions and divide into 16 cell morula. • Internal Cells= Internal Cell mass (ICM) • Most external cells become trophoblast.

  5. Early Cells in Mammalian Embryo • Totipotent • Pluripotent

  6. Cavitation. • Trophoblast cells secrete fluid into Morula: blastocoel • Trophoblast Na+ pumps are activated by oviduct cells.

  7. Hatching of Mammalian Blastula • Zonapellucida prevents embryo from attaching to oviduct wall. • Trypsin like protease: releases embryo from ZP.

  8. MammalianGastrulation • Mother provides nutrients • The reliance of embryo on Mother has resulted in fetal organs • Chorion • Hypoblast/epiblast • Germ disc • Amniotic cavity

  9. Mammalian Gastrulation: Primative Groove

  10. Extraembryonic Membranes • Trophoblast cells make up cytotrophoblast and syncytiotrophoblast. • Trophoblasts and Uterine tissue: Placenta

  11. Axis specification in Mammals • Two signaling centers • Node • Anterior Visceral Endoderm(AVE) • Work together to form anterior region. • Notochord: dorsal infolding of small ciliated cells • AVE: visceral endoderm migrates forward. • Antagonists of Nodal • Lefty-1; Cerberus • Nodal activates expression of posterior genes; Lefty-1 and Cerberus blocks this activity

  12. Axis Specification: Anterior-Posterior positioning • FGF and Retinoic acid gradients. • Ultimately leads to differential expression of Hox genes

  13. Anterior-Posterior Axis: Hox Code

  14. Retinoic Acid and Hox Gene Expression

  15. Dorsal-Ventral and Left-Right Axes • DV axis formation: Poorly characterized. • Left-right axis formation: Nodal and Pitx2

  16. Early Development of Birds: Cleavage

  17. Gastrulation: Birds • The Hypoblast • The primative streak

  18. The Primitive Streak

  19. Primitive Streak: Molecular mechanisms of migration

  20. Regression of Primitive streak

  21. Axis specification in Birds • Gravity and PMZ

  22. Left Right Axis

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