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Transcript
Review from last lecture • Cell signaling • Fertilization (3 ligand-receptor pairs) – Resact/receptor – Jelly coat factor/receptor – Bindin/fertilizin • The acrosome reaction • Preventing polyspermy Outline Questions Understanding Cell Proliferation and Cleavage • How is cell proliferation used in the growth of developing tissues? • What are the post-fertilization stages of development? – How many cells do they have? • What is cleavage? – What are the different forms of cleavage found in different animals? • What are maternal determinants – How do they direct early development? – How can this help to define body axes? • How do cells move? – What structures are created or destroyed to give directional movement? Bio200 Proliferation and Cleavage Cell proliferation • If cells are signaled correctly, they will begin proliferating – Controlled but rapid mitosis – Good for building or restoring structures – Cells sometimes made in large amounts, and then differently regulated to several cell fates Cell proliferation • If cells are signaled correctly, they will begin proliferating – Controlled but rapid mitosis – Good for building or restoring structures – Cells sometimes made in large amounts, and then differently regulated to several cell fates • The initial proliferation from zygote to embryo is called cleavage – This refers to the cleavage furrow, which is the earliest readily-recognizeable feature of cell division – Often driven by packaged material in the oocyte – Maximizes speed of growth, as the cell does not have to wait for massive transcription and translation Cell division http://www.youtube.com/watch?v=28GTvrNvRRE These were taken at the same magnification. What can you tell about cell size? Cleavage Patterns: Examples Fertilized egg Radial cleavage: Spiral cleavage: Discoidal cleavage: Blastula Example: Many deuterostomes Example: Snail Example: Birds Yolk Superficial cleavage: Example: Fruit Fly Cells Yolk Cleavage Patterns: Examples Fertilized egg Radial cleavage: Spiral cleavage: Discoidal cleavage: Blastula Example: Many deuterostome Example: Snail Example: Birds Yolk Superficial cleavage: Example: Fruit Fly Cells Yolk Cleavage Patterns: Examples Fertilized egg Radial cleavage: Spiral cleavage: Discoidal cleavage: Blastula Example: Many deuterostome Example: Snail Example: Birds Yolk Superficial cleavage: Example: Fruit Fly Cells Yolk Cleavage Patterns: Examples Fertilized egg Radial cleavage: Spiral cleavage: Discoidal cleavage: Blastula Example: Many deuterostome Example: Snail Example: Birds Yolk Superficial cleavage: Example: Fruit Fly Cells Yolk Rapid progression from one cell to many http://www.youtube.com/watch?v=XSKh-GLQn4E Early stages of development: Common terminology • Zygote – 2N fertilized post-oocyte cell • Morula – A small ball of cells resulting from early proliferation • Blastula – Hollow ball of cells, where regulation has started cell movements Early stages of development: Common terminology • Zygote – 2N fertilized post-oocyte cell • Morula – A small ball of cells resulting from early proliferation • Blastula – Hollow ball of cells, where regulation has started cell movements • Early Gastrula – Larger embryo, either having or starting to have formed cell layers • Late Gastrula – Significantly developed early embryo, with cell layers formed Maternal determinants: Pre-loaded developmental material • Follicle cells allow the mother to load materials into the egg – Nutrients – Directions! • Information-containing molecules that help the young egg develop • Could be proteins, RNAs, etc • Spatial localization is crucial What are cytoplasmic determinants, and how do they affect the consequences of cleavage? • Stylea partita has ~transparent embryos so you can follow fate of cells, based on pigmented areas in egg. • Observation 1: From “fate mapping” • What can you conclude from this observation? Transcription in early embryos Experiments with α‐amanitin (Amanita = “death cap” and “destroying Angel” mushrooms): inhibits RNA polymerase. In frogs: cleavage occurs normally if embryos are treated with α‐ amanitin. What can you conclude from this observation? Preferential polymerization: Directional and signaled crawling nucleus Preferential polymerization: Directional and signaled crawling nucleus Cell Movement Video http://www.youtube.com/watch?v=sHFN48il9YY Cell actions in development Key Concepts • • • • Cell proliferation is the use of repeated rounds of mitosis to build tissues by increasing the number of cells. Most zygotes undergo cleavage and then go through the following early-development stages: morula, blastula, gastrula Different species use different cleavage geometry and patterning. Within a species, all cleavage patterns will proceed from one cell to many organized cells. Specific RNAs and proteins deposited in the oocyte by the mother help to jump-start development. • • • Cells can move: • • • • Using the polymerization and depolymerization of filaments In response to signals Directionally, by preferentialy locating polymerization enzyme in the cell The five basic processes by which cells help to create a developing organism are: • • • • • • These maternal determinants may help define early developmental decisions. Maternal genotype may determine some of the embryos phenotypic characteristics. Apoptosis Differentiation Signaling Proliferation Movement Organisms use these basic processes in rigorously controlled combinations to ensure development of new, complicated, consistent structures.