Lec 8: Mechanisms of Development Flashcards Preview

Unit 7 - MCP > Lec 8: Mechanisms of Development > Flashcards

Flashcards in Lec 8: Mechanisms of Development Deck (26):
1

Genes govern cell development

proliferation, specialization, interaction and movement and cell-cell communication

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homologous genes can function interchangeably during the development of different species

a gene similar in structure and evolutionary origin to a gene in another species. (eg. a drosophila gene input into a mouse will serve the same function as it did in the drosophila)

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Genomic equivalence

all cells contain the same set of genes, the genetic material is identical in every cell but different cells express different sets of genes

4

Somatic nuclear transfer is a perfect evidence that all cells contain the same genes

it didn't lose any of the genetic material

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How do genes drive development of different tissues when all of the genes are the same in every tissue?

differential gene expression/transcription - where only a small percentage of the genome is expressed in cell type
So like in one cell you will have genes, 1,2,3 but only express gene 1...while in another cell you have the same genes but only express genes 2,3.

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Expression of genes at every level

differential gene transcription
• selective nuclear RNA processing
• selective mRNA translation
• differential protein modification

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Differential gene expression

RNA localization by in situ hybridization....used to detect mRNA expression in cells or tissues...use a probe to detect where the cells are located

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How do you turn on differential gene expression...how do cells know which genes to turn on and which to turn off?

Inducer cells and responder cells. Inducer cells induce other cells but responder cells have the ability to respond...and those that do have the ability to respond are called "competent"

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Eg. with tadpole: you need BOTH the inducer and the responder in order to be present in order for eye differentiation to occur.

The optic vesicle is able to trandsuce lens formation in the head ectoderm. However if the optic vesicle is placed in a different loaction (e.g. trunk) that ectoderm will not form a lens. Only the head ectoderm is competent to respond to the signals from the optic vesicle. if the optic vesicle is removed, the surface ectoderm fails to form a normal lens. Other tissues are not able to induce lens formation.

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Competence is actively acquired!

Pax6 makes ectoderm competent to respond to inductive signals from the optic vesicle. No PAX6 no eye development. Same in humans

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Juxtacrine signaling

physical contact between the inducing and responding cells. Both cells have to be right next to each other

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Paracrine signling

no physical contact needed but they are in close proximity.

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Morphogens (subset of paracrine) act in a concentrating manner

A morphogen is a paracrine signaling molecule from a source that acts directly on neighborhing cells to produce specific responses that depend on concentration of the morphogen.
Ex. a high conc gradient may direct cells to develop into one pathway vs, a conc gradient in another pathway

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The morphogen mechanism and cell response

The cell that is closest to the secreting cell will get higher conc of signaling and will respond differently than another cell which is farther away and is receiving a little less signaling

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Signaling cascade shows the stepwise relay of information within a cell. If one of those steps is missing or affected, then the cell

may no longer be competent. You need the entire complex, not just the morphogen

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Hedgehog Signaling pathway

SHH is the ligand, it binds Pathched (a Receptor) and this inhibits Smoothened which normally GLI transcription factors

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Morphogen gradients in the neural tube

2 competing gradients that set up the doral vantral polarity;
SHH (secreted from floorplate - high at ventral, lower conc towards the dorsal)
BMP (secreted from roofplate - high at dorsal, lower towards ventral. Together the specify different cell types in their exact location

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Left right body axis

defects in embryogenesis (heterotaxy) leads to congenital malformations Nodal only on left

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Kartagener's triad: bronchiectasis, infertility and situs inversus (inverted organs)

A clue to initial asymmetry of Nodal expresssion

Clue that ciliary beating controls which way the left-right axis is oriented - embryonic node, the organizer has motile cilia - generates a right to left fluid flow. Cilia generates nodal flow asymmetric. Possibly due to setting up a morphogen gradient - only on the left side of the embryo.

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Goal of nodal transcription factor is to turn on PITX2

which is expressed only on the left side

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Summary

Pathway used by most vertebrate embryos, same gene in humans
differntial gene expression in lateral plate mesoderm...only expressed on one side not on R side.
Cell cell signaling can turn on itself, its target etc.

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Q.1How do somatic nuclear transfer experiments provide evidence supporting the idea of genome equivalence?

Since the nucleus of an adult somatic cell can generate a new adult animal, this indicates no genes were lost during cellular differentiation

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Q2. A patient with reversed left-right asymmetry of the heart but otherwise normal arrangement of internal organs would be classified as

heterotaxy

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Q3. A morphogen concentration gradient is used to

divide a field of cells by specifying more than one cell type

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Q4. The optic vesicle induces lens formation in the head ectoderm but not in trunk ectoderm. What is the best explanation for this obversation?

only the head ectoderm is competent

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Q5. A research group investigating a gene in zebrafish called Southpaw (Spaw) that encodes a protein with high sequence similarity to human and mouse Nodal proteins. When they expressed Spaw in left lateral plate mesoderm (LPM) in mouse mutants that lack LPM Nodal expression, they found that the left-right body axis defects usually observed in the mutant embryos were rescued. What were they able to conclude?

Spaw and Nodal are homologous genes!