Topic.2.Development.powerpoint.2.3.Developmental.mechanisms Flashcards
What are the two mechanisms underlying development?
Cytoplasmic determinants
signaling molecules
What are cytoplasmic determinants?
Maternal substances in the egg that influence gene expression in a localized area
Ex: mRNA encoding transcription factors,
How do signaling molecules influence development?
Signaling molecules from neighboring cells
Ex: certain signal molecules cause specific changes in gene expression sending the cell down a specific developmental path
Cells make developmental decisions by responding to
___ in their internal ___. They make developmental decisions within a __ and __ framework.
signals, local environment
temporal, spatial
What is the mechanism underlying development in P granule localization in c.elegans?
Cytoplasmic determinants
P granules are complexes of RNA and protein
Initially distributed throughout zygote but are repositioned to posterior end of zygote, found in P4 blastomere which gives rise to gametes.
Essentially p granules being localized to one area, categorize those cells fate of being gametes
Give me two example that show how the body plan is predetermined in frogs?
Frog:
A/P determined during oogenesis
D/V determined at fertilization
What is the evidence that shows frogs A/P was determined during oogenesis?
Dark melanin granules found in animal hemisphere
Yolk in vegetal side
What is the evidence that shows frogs D/V was determined during fertilization?
Cortical rotation: plasma membrane rotates toward the point of sperm entry, which enables molecules in parts of the vegetal cortex to interact with molecules in the animal cortex leading to specific gene expression
What evidence gives rise to the body plan in chicks before fertilization?
A/P axis may begin to be established by gravity as the
eggs moves down oviduct
What is the other evidence that gives rise to body plan in chicks?
pH differences between the two sides of the blastoderm
cells lead to D/V patterns
What creatures are a good example of pattern formation?
Pattern formation: the development of a spatial organization in which the tissues and organs of an organism are all in the right place.
Insect: Axis formation
Often involves morphogenetic gradients
Morphogen
A substance that creates a concentration gradient across a developing tissue, governing the tissue pattern and positions of specialized cells within tissues
Morphogenetic gradients generate_
different cell types in distinct spatial order, meaning certain area of tissue will have specific cells
Morphogens are the products of __ or __
genes, signaling molecule(retinoic acid)
What are some genes of bicoid?
Morphogens can be products of genes.
Homeobox gene: encodes for a transcription factor
Maternal effect gene: when it is mutant in the mother, the offspring will have a mutant phenotype regardless of their
own genotype
bicoid gene: sets up Anterior side larva, default is posterior
How does mRNA in bicoid relate to morphogens?
We known morphogens create a concentration gradient that leads to spatial cell specialization.
Bicoid:
mRNA is concentrated at A end of the mature egg, once fertilized it’s transcribed into protein. Then protein diffuses toward the posterior, resulting in a gradient aka morphogen. Bicoid bind to enhancer of genes involved in pattern formation, and turn on cells to form anterior structure.
What drives further differentiation of general categorizes in fruit flies?
Ex: posterior and anterior
Maternal mRNA is destroyed and the embryonic program of gene expression takes over to refine. Embryonic genes start encoding proteins and signaling molecules that are involved in gene activation/repression
What are the major classes of developmental genes in drosophila?
Maternal effect genes
Gap genes
Pair-rule genes
Segment polarity genes
Hox genes
maternal effect genes are a major class of developmental genes in drosophilla. Why so?
Maternal effect genes - set up the A/P and D/V axis polarity
gap genes are a major class of developmental genes in drosophila. Why so?
Gap genes - affect the development of a contiguous block of segments
Ex: kruppel- establish central part of fly
pair-rule genes are a major class of developmental genes in drosophila. Why so?
Pair-rule genes - control the proper development of adjacent
Ex: even-skipped
segment polarity genes are a major class of developmental genes in drosophila. Why so?
Segment polarity genes - affect individual segments’ polarity. Ex: engrailed,wingless
hox genes are a major class of developmental genes in drosophila. Why so?
Hox genes - affect the identity, characteristics of a particular segment
Ex: Abdominal A
Hox genes are homologs meaning?
genetic sequences of Hox genes and their positions on chromosomes are remarkably similar across most animals because of their presence in a common ancestor
Hox genes signify the A/P axis because?
The genes are expressed from (3->5), 3 being anterior end and 5 being the posterior
Vertebraes can have 4 copies of hox gene due to _ and _
gene duplication and divergence
Hox genes specify ___, not specific structure
positional identity
The products of hox genes are hox proteins. Which are _
transcription factors as they are capable of
binding to specific nucleotide sequences on the DNA called
enhancers where they either activate or repress genes.
TF Hox protein can only be a repressor
False: same Hox protein can act as a repressor at one gene and
an activator at another.
In a chick, what is a limb bud?
mesodermal tissue covered by ectoderm
Differential Hox gene expression cause
specific cells in the limb bud to react differently to positional cues; meaning each part of the limb develops at precis location due to positional information
What is an example of temporal/spatial refinement in hox gene expression of limb?
Different Hox genes are
“turned on” as limb
development progresses
What are the two main organizing regions in the limb bud?
AER: apical ectodermal ridge
ZPA: zone of polarizing activity
AER
dense ecto at outer edge of bud that lead to P/D organization and secretion of proteins in FGF (fibroblast
growth factor) that promote bud
outgrowth
ZPA
ZPA: meso tissue on posterior end of the limb that sets up A/P; close to ZPA creates posterior structures and far from ZPA produces anterior
ZPA secrete SHH (signaling molecule and transcription factor) that specifies limb growth and digits
What are the key genes in limb development?
Hox genes: homeobox, transcription factors; specify the
“limb field” or “pre-pattern”
FGF: fibroblast growth factor, from AER cells, for limb outgrowth
SHH: Sonic Hedgehog; secreted signaling molecule, from ZPA, involved
in A/P patterning, specifies digits
WNT7: signaling protein found in dorsal limb ectoderm, involved in D/V
patterning (also neural tube development, cancer-colon)
BMP: bone morphogenesis protein; involved in interdigit programmed
cell death (regulates AER- FGFs )
The cytoskeleton is a mechanism that underlies development, because?
Cytoskeletons are networks of proteins in cytoplasm that provide the cell with structure and shape. They can cause changes in cell shape and migration
How does the cytoskeleton relate to neurulation?
Microtubules extend and
elongate the neural plate cells
Actin filaments at one end of the cell
contract; cells form a curved shape
.Curved chnages results in the pinching off of neural tube
What is cell migration, give an example
Cell migration:Cell’s “crawl” within an embryo by extending and
retracting cellular protrusions.
Ex:Neural crest cells (migration from neural tube)
Actin polymerization and depolymerization can explain __
cell migration:
moves leading edge forward.
Contraction at back propels cell body forward.
Cell migration involves _ and __
cell adhesion molecules and ECM(contains molecules secreted by cell)
Fibronectin can help bind _
Integrins; receptor proteins found on the surface of cells
Important because it affects cytoskeleton
Apoptosis is another mechanism underlying cell death. Apoptosis is
programmed cell death
Ex: reabsorbation of tadpole tail
