2-36 Mechanisms of Development Flashcards Preview

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Flashcards in 2-36 Mechanisms of Development Deck (24)
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what allows us to use animal models?

genetic similarities. 40% of human genes are found in flies and roundworms


what are homologlous genes?

Genes found in different species that are similar in structure, in evolutionary origin, and likely in function as well. (e.g. A mouse that artificially produces a homologous fruit fly brain developmental protein still has successful brain development.)


what is the idea of genome equivalence?

The idea that every cell in the body contains the same genome. Proven by cloning "dolly" the sheep with a single skin cell.


Differential Gene Expression

The idea that different cell types express different genes.



– The act by which one group of cells (inducers) changes the behavior of an adjacent group of cells (responders). It is carried out by chemical messengers, either through cell-cell contact (short-range) or by sending the messenger through the ECM (long-range). Only competent cells will be able to respond to and/or receive those signals. Competence of cells is actively acquired.


optic lens example

offshoot of neural tube called optic vesicle induces ectoderm cells to form lens when in contact with the ectoderm.

if optic vesicle removed OR added to other part of frog, the ectoderm will not form a lense

proper inducer and proper responders (in this case with expression of PAX-6 TF in the cell)

expression of Pax6 grants competence to the responders



when an individual lacks a copy of the Pax6 gene

-several eye structures including the iris and optic nerve are affected

lacking both copies leads to a fatal condition



paracrine signaling molecule that cause concentration-dependend events.

can generate more than one cell type by establishing a gradient in conencretation (different concentrations throughout the gradient will direct cells into different developmental pathways


signaling cascades

occur via juxtacrine (cell-cell direct) or paracrine

when signal received - cascade directed by intracellular proteins leads to altered metabolism, altered gene expression, and altered cell shape/movement


describe the TGFb signaling pathway

begins with cell surface receptor recognition of a TGFB family molecule (TGFb, BMP, and Nodal)

2. SMAD transcription factors are phosphorylated - move to nucleus and modulate gene expression


the internal organs are placed asymmetrically within the trunk of the body. what is the key to this?

asymmetric gene expression which is facilitated by ciliary beating by ciliated cells which creates an uneven distribution of Ca+2 favoring the left side

the signal is then relayed to create a broad stripe of nodal expression in the lateral plate mesoderm solely along the left side of the embryo body, leading to differential gene expression


describe nodal and what it does

nodal is a secreted molecule that turns on transcription of itself and downstream TF PitX2 and antagonist lefty.



upregulated by nodal - lefty functions to restrict the asymmetric domain of nodal signaling by keeping gene expression exclusively on the left side of the embryo



upregulated by nodal - expressed on left side of developing heart, gut, and brain. thought to regulate expression of genes that mediate asymmetric morphogenesis of these organs


incorrect localization of gene expression leads to

changes in body asymmetry, as opposed to normal situs solitus.

inverted layout - situs inverses - no clinical issues
situs ambiguous - irregular layer


calcium is a morphogen, TF

calcium is not a morphogen. it is a downstream effector


describe role of cilia

creates asymmetric flow which generates areas with higher signaling calcium on the left, causes nodal signaling that turns on other genes. these genes are important for forming asymmetries as heart and gut begin to develop


how can drugs alter developing symmetry?

if they elevate or reduce calcium levels


Kartagener's Triad

due to immotile cilia

bronchiectasis - cilia unable to move mucus out
infertility - sperm flagella non-motile
situs inversus (50%)


cardiac looping to the right is...

highly conserved and important in vertebrates


sonic hedgehog protein does what?

binds receptor, inhibits activity of another receptor, represses gene expression


describe competence molecules

on a molecular level, all of the docking proteins, signaling molecules, and effector proteins that lead to altered metabolism, altered gene expression, or altered cell shape/movement


genes in the embryo can be

differentially regulated and timing is important

regulated by
-differential gene expression
-selective nuclear RNA processing
-selective mRNA translation
-differential protein modification


if all the genes in all cells are the same, how do we get differentiation?

through differential expression.

only a small percentage of the genome is expressed in each cell type

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