Determinant Development

Chapter 21.2

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Genomic Equivalence

Genomic Equivalence – all cells have the same genome

Despite genomic equivalence, there are differences in the cells of multicellular organisms

These differences are due to regulatory mechanisms

So although all cells have the same genome, due to differential genetic regulation, they can look and function dramatically differently.

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Pattern of Development

Development is governed by a combination of cytoplasmic determinants & inductive cell signals

Cytoplasmic determinants Chemical signals such as mRNA & transcription factors

that were distributed unevenly during cleavage

Induction Interaction among cells that influence their fate Causes changes in gene expression among cells

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Totipotent Cells

Cells that are capable of developing into ANY possible cell type As long as it possesses the requisite genetics, it can

become muscular, nervous, epithelial, etc. If you have a totipotent cell, you can literally grow

another organism, and you can grow as many as you would like

Totipotent cells exist until the 16-cell stage of cleavage

After that, they are pluripotent – can become any of the 3 germ layers, but cannot develop into a new being

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Totipotency in Plants

Plant cells are totipotent throughout their lifetime

Basically plant cloning is easy to do at any stage of development.

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Totipotency in Animals

Some animal cells could be considered totipotent (kind of), but some were not.

Older nucleus donor = LOWER chance of development

So animal cells change over time in terms of what they can become.

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Reproductive Mammal Cloning

1997 “born”

2003 euthanized due to respiratory complications usually seen only in older sheep (mom’s age) Also had arthritis, which is unusual for Dolly’s age, but not for mom’s

Reproductive clones do NOT look like mom or the source of the nucleus.

Clones of mice, horses, cattle, etc have been successful, with defects.

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Cloning Caturday

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iPS Cells

iPS – Induced pluripotent stem cells

Take an adult (fully differentiated) cell, modify the signaling being received, thus altering the genetic expression of certain “induction” genes

Future of medicine?

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Dr. Eric Lander’s AMA (2/21/13)

AxelHarver - What do you think is the "coolest" scientific discovery we've made so far in the 21st century? Eric_Lander[S] - I think Yamanaka's discovery

that adult cells can be "reprogrammed" into stem cells was mind-blowing. Completely unexpected. Huge impact.

Nobel Prize in Physiology or Medicine 2012: http://www.nobelprize.org/nobel_prizes/medicine/laureates/2012/#

http://www.sciencedirect.com/science/article/pii/S0092867406009767

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Determination

Term used to describe the condition when a cell is irreversibly committed to its fate

Once a cell is differentiated, it expresses genes for tissue-specific proteins

Myoblast

Determined muscle cellDifferentiation follows determination by MyoD (transcription factor)MyoD also causes G0 state