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Bio 20B - (Chapter 19) - Animal Development (1)

Terms in this set (63)

Determination
Setting the fate of the cell.
What kind of cell will it become?
Will it become a Kidney cell? Heart cell? Liver cell?

Once fate for that cell has been set, caused to be on a path to become this cell.
Differentiation
The process by white different cell types arise to perform different functions.

Once the cell turns into the cell -> makes unique cells (ex. forms heart -> will become cardiac cell which is much different and has different functions compared to kidney cells)

Determination is a commitment; the final realization of that commitment is differentiation
Morphogenesis (Origin of Form):
How differentiated cells get organized spatially.

Concerned with the shapes of tissues, organs, and the positions of cells, body plan.

It is the result of differential gene expression, cell-cell signaling, and is linked in with growth.

(How we end up with 2 arms, 2 legs, and symmetry of those)
Growth
Increase in body size, organ size, by cell division and/or cell growth

Animals - favor cell division
Plants - favor cell enlargement
Differential Gene Expression
The expression of different genes within different cell types. All cells have whole genomes but they express those genes differently.

It results from differences in gene products within a cell.
(only reason why differentiation and determination can occur)
(Ex: Mutant Fruit Fly having legs placed where the antenna should be - tells us that the genes are there, but they're inappropriately expressed)
Determination and Differentiation proceed because of
differential gene expression
Morphogenesis and growth occur by...
Cell divison, expansion, movements, apoptossi
During development, cell fates become increasingly_______. Timing varies but it usually___________.
restricted, happens early
How can we tell WHEN a cell has become determined or not? What is an experiment that you can do to determine that?
Transplant Experiment!

After the fate of a cell has been determined, it can be tested
by transplanting a cell from one part of an embryo
to a different part of a recipient embryo, seeing
if it adapts to its new surroundings or will continues on
its previous path.

If you take a cell from an embryo that would, when in the cell, normally transform into a kidney cell and put it into a different embryo in a different location. This cell is determined bc no matter what the cell tried to do to it, it was already of the path to become a kidney cell.

Or hand, if you take the cell that'll become a kidney cell and you put it into another location in the embryo and it turns into whatever it should be -- less determined.
Totipotent
The cell can differentiate into anything. (all capable)

Capable of developing into complete organism.
Pluripotent
Cell can differentiate into most cells by NOT new embryos.(many capable)
Multipotent
cell can differentiate into several related cell types (ex. all cells in kidney but not in the heart)-several capable
Unipotent
cell can produce only its same cell type (one capable)
What mechanisms make a cell tun into a particular cell type?
Cytoplasmic segregation, induction
Cytoplasmic segregation
unequal cytokinesis; some factor (cytoplasmic determinants) is unevenly distributed within the cytoplasm.
Cytoplasmic segregation results in______ which forms the___________and the _________.
Polarity, animal pole, vegetal pole
Cytoplasmic determinants are
mRNAS, transcription factors , proteins which lead to genes
Cytoplasmic segregation can lead to
differential gene expression
Animal pole
named bc the cells tends to be more active and divide faster
Vegetal pole
divide slower, it's where we find yolk in these species that have them.
Induction
- cell to cell communication; a factor is made and transported to induce other cells to differentiate.

- Varies, can turn on different genes, can turn off different genes - underlying idea is that it causes the cell to do something different
Cell polarity
- spatial differences in the shape, structure and function of cells
Concentration gradient of the inducer cell affects gene expression of nearby cells. Once it hits a _____, the signal transduction pathway is triggered and the transcription factor moves to nucleus or is otherwise activated.
threshold
Factors
- made and transported to induce other cells to differentiate (turns on different genes
What is the difference between cytoplasmic segregation and induction? Both of these mechanisms can lead to differential gene expression, how?
Cytoplasmic segregation - have a cell with "factors" which are unevenly distributed - when the cell divides, the factor will be unequal in daughter cells. This sets us up to get to differential gene expression, one of the cells is going to have a gene that is turned on by the transcription factor, while the other is not. At that point, we've set up a trajectory for the these two cell line to develop into different things.

Induction - cell-cell communication - one cell will make a "factor," release, goes and binds to a receptor on nearby cells, potentially causes a signal transduction cascade, can then lead to differential gene expression in that cell (ex: development of froghead lens)
Signal transduction pathway
- Occurs when an extracellular signaling molecules activates a specific receptor located on the cell surface or inside the cell.
- Receptor triggers a biochemical chain of events inside the cell, creating a response.
- Alters gene expression
__________ _________ act as molecular switches during development.
Transcription factors
Patterns can arise via...
apoptosis, morphogen gradients
______ ______ _______ underlies/controls these processes.
Differential gene expression
Morphogen
A special type of inducer that relays positional information to a cells (signal molecules)
1. Must directly target cells rather than triggering a secondary signal
2. Different concentrations of signal must cause different effects
Apoptosis
Programmed cell death. (Cells between digits die to form free fingers and toes)
Genes & mechanism that control apoptosis in C. elegans very similar to ____ pathway
human
The French Flag Model
Shows how when cells are exposed to different concentrations of inducers, they will result into different phases and differentiate to form a pattern. Within this model there's a high, medium, and low concentration of induces, which results in this concept of the "French Flag" because it induces the cells into 3 different fates.
Lewis Wolpert
came up with French Flag model (late 60s)
-Cells have positional identity depending on morphogen gradient
Zone of polarizing activity
- creates morphogens
Sonic Hedgehog
- morphogen
- induces the formation of a digit
-Little finger forms when there is a lot of Shh
How can these morphogen gradients lead to formation of complex patterns?
Complex patterns formed by a cascade of
transcription factors released in a specific sequence & which form morphogen gradients
Maternal effects genes
phenotypes that are controlled by nuclear factors found in the cytoplasm of the female (mom).

Genes in the mom → transcribed to mRNA → positioned unevenly in a cell (specifically deposited into 1 end of the embryo)
MEG generally about
anterior posterior
(and dorsal ventral) axis
There are two maternal genes which are_____and _________ and diffuse as _______ into future_________ end of egg.
Bicoid and nanos, mRNA,Anterior
Bicoid
mRNAs diffuse from the mother's cell into the anterior end of the egg. Once inside, diffuses towards the posterior and creates a concentration gradient.

(Bicoid and nanos are both found in the mom)
Nanos
egg's cytoskeleton moves the mRNAs of Nanos to the posterior end where it is translated. Inhibits the translation of Hunchback mRNAs

(Bicoid and nanos are both found in the mom)
Maternal effect genes eventually turn on...
segmentation genes
Segmentation genes
The number, boundaries, and polarity of the Drosophila larval segments are determined by proteins encoded by these genes.
There are three types:
Pair Rule, Gap Genes, and Segment Polarity Genes
Pair Rule Genes
divide the embryo into units of two gements each. Mutations in pair rule genes result in embryos missing every other segment
Gap Genes
- organize broad areas along the anterior-posterior axis. Mutations in gap genes results in gaps in the body plan - omission of several consecutive larval segments
Segment Polarity Genes
- determine the boundaries and anterior-posterior organization of the individual segments. Mutations in segment polarity genes can result in segments in which posterior structures are replaced and reversed (mirror-image) anterior structures
Hox genes
- (organ will be made at a given location)
- have common base pairs called homeobox (encodes for 60 AA sequence called homeodomain)
- order that they are in the chromosome corresponds to the order that they are in the body
-common acorss many animals with an AP axis
- ex: head hox gene 1st on chrom., 2nd thorax, abdomen 3rd. in chrom.
Hunchback
- created by bicoid and nanos concentration gradient
- gene that is expressed when there is sufficient amount of bicoid present
- starts off evenly distributed -> bicoid and nanos have different plans for it
- nanos prevents translation of hunchback (so it strays out of the posterior end of the gene)
- bicoid increases translation (hunchback heavily prevalent in the anterior portion of gene)
- important because it triggers the formation of anterior (head) structures
Homeobox
DNA sequence found in Hox genes and other genes that code for transcription factors
Embryonic Stem Cells (ESC)
Group of cells in the blastocyst of mice and humans; can give rise to most cell types, but not new organism
Induced Pluripotent stem cells
Induce adult skin cells back to an undifferentiated state; can make many cell types
What do the products of Maternal Effects Genes, Segmentation Genes, and Hox genes all lead to?
THEY ALL LEAD TO DIFFERENTIAL GENE EXPRESSION
What does the cascade of sequential morphogen gradient lead to?
Maternal effect genes → Segmentation genes → Hox genes → leads to more complex body pattern. (finer and finer body patterns)
What are stem cells, and how are they used?
Stem cells are rapidly dividing undifferentiated cells that can differentiate into diverse cell types. These stem cells are used to repair/replace organs, tissues, treat cancer, and clone valuable/endangered animals or species.
First time stem cells were isolated:
-Steward -> Isolated cells from carrot root and kept them in a medium → able to revert them to totipotency (all cells or embryo) → cells able to turn into a complete embryo
Are all stem cells created equal?
No, they vary in being adult/embryonic. What's really diff. bet. adult stems cells (multipotent - in bone marrow) and embryonic stem cells ->
Embryonic Stem Cells (ESC) -
Group of cells in the blastocyst of mice and humans; can give rise to most cell types, but not new organism
Induced Pluripotent stem cells -
induce adult skin cells back to an undifferentiated state; can make many cell types
What are advantages of induced pluripotent?
Can make many cell types, no controversy compared to ESC, avoid immune sistem complication
Hematopoietic Stem Cells
Blood Cells
Mesenchymal Stem Cells
Bone, connective, muscle cells
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