Midterm Flashcards
MeCP2
the protein which this gene codes for binds methylated cytosine residues. It recruits histone deacetylases (which remove acetyl groups from the histones) or methyl transferases (which add methyl groups to histones)
BOTH repressing gene expression!
histone acetyltransferases
HATs - These add acetyl groups onto histones. This PROMOTES GENE EXPRESSION because the positive charge on the lysine residue is neutralized by the acetyl group and thus does not bind tightly to the negatively charged DNA - loosens the DNA
histone methyltransferases
Transfer methyl groups onto histones
- this usually represses gene expression
histone deacetylases
Remove acetyl groups from histones
This represses gene expression.
Rett Syndrome
Debilitating neurological disorder in females. Mutation of the MeCP2 gene which lies on the X chromosome.
The gene is haploinsufficient. So men who have mutated MeCP2 gene will die before being born.
Where is the Pax6 gene expressed?
lens, cornea, retina, in the neural tube, and in the pancreas
Blastomere
The cell of any cleavage stage embryo
neurula
Name from an embryo that has a neural tube forming (we won’t use this term for mammals)
meroblastic cleavage
when the entire egg is NOT cleaved into cells (ie. some is cleaved into something else)
holoblastic cleavage
the entire egg is cleaved into cells (so the entire egg becomes part of the embryo - minus any extracellular material)
What does specification mean?
When a cell is committed to a given fate, but this commitment can still be reversed. In this stage, a cell will differentiate along a certain path (unless the signaling or environment changes).
- In this stage, a cell can differentiate autonomously (by itself) into a specific cell type in a neutral environment
- This is the only stage of commitment where the fate of the cell can be changed
What does determination mean?
The stage of cell commitment where its given fate is irreversible. Changing the environment will no longer have an effect on what the cell differentiates into.
- When a cell can differentiate autonomously AND its fate cannot be reversed from signals.
What does differentiation mean?
Development into a specialized cell type. At this stage, the cell is overtly of a certain type at a biochemical and functional level
- See literal changes to the cell function here
Autonomous specification
Blastomeres acquire determination factors from the egg cytoplasm
- They have some factor within the cytoplasm that specifies them towards a certain fate.
- A mode of cell commitment in which the blastomere inherits a determinant, usually a set of TF’s from the egg cytoplasm, which regulate gene expression to direct the cell into a particular path of development
- tunicates
Conditional Specification
Embryonic cells are specified by external signals from their neighbouring cells.
ex. Removing cell from 4 cell embryo - each piece will develop fine because they are conditionally specified and thus their fate hasn’t been internally determined yet.
- The ability of cells to achieve their respective fates by interactions with other cells. (paracrine factors)
What type of tissue is the notochord derived from?
The mesoderm. The notochord later develops into the vertebral column.
Epithelial to mesenchymal transition (EMT)
Transition of cells from an epithelial sheet to individualized migratory cells. This is important in developmental processes and cancer.
Invagination
Type of cell movement during gastrulation (formation of 3 germ layers)
- In folding of sheet of epithelium of cells. Indentation of a ball. Cells are entering inside the embryo without contacting the outside layer
- Neural tube originally forms from this process
Involution
Inward movement of an expanding outer layer so that it spreads over the internal surface of the remaining external cells. Outer layer becomes inner layer - outer and inner in contact.
migration of sheet of cells
Ingression
Migration of individual cells from the surface of the embryo’s interior. Individual cells become mesenchymal (separate from one another) + migrate independently. These cells will become meso- and endoderm in mammals
delamination
splitting of one cellular sheet into two more or less parallel sheets. End result is formation of a new additional epithelial sheet of cells.
epiboly
movement of epithelial sheets (usually ectodermal) spreading as a unit to close deeper layers of the embryo. Can occur by cells dividing, cells changing their shape, or by several layers of cells intercalating into fewer layers.
What tissues are derived from the ectoderm?
Epidermal (skin) cells, nervous system, neural crest, pigment cells
What tissues are derived from the mesoderm?
Connective tissue, notochord, red blood cells, bone and muscles
kidneys, gonads
What tissues are derived from the endoderm?
Digestive tube (gut), stomach cells, pharynx, thyroid, lungs, inner linings
What is syncytial specification?
- Predominates in most insect classes
- Specification of body regions by interactions between cytoplasmic regions prior to cellularization of the blastoderm
- Variable cleavage produces no rigid cell fates for particular nuclei
- After cellularization, both autonomous and conditional specification are seen
Syncytium
A cytoplasm containing multiple nuclei. Cell membranes haven’t formed around nuclei
Morphogen
A long range signaling molecule that forms a concentration gradient in the specification/determination of the cell depends on the concentration of the molecule
Nuclear genes are differentially activated by the differing ratios of morphogens present in the given location
ie. bicoid, nanos, caudal
- A morphogen influences the fates of other cells, as it diffuses
In a syncytium, a TF can act as the morphogen because it never leaves the cytoplasm. In mammals, TF can’t leave cells and thus cannot act as morphogens or signaling molecules.
To function as a morphogen, a protein must be able to diffuse to form a concentration gradient.
Determinant
Influences cell fate in the cell which it is found or produced
What are features of all early vertebrate embryos?
Primitive kidneys, gill arches, notochord, a spinal cord, and a neural tube flanked by somites.
- Gene expression is most similar among different types of vertebrate embryos when these similar features are observable.
What is a chimeric embryo?
An embryo made from tissues of more than one genetic source
Homologous structures
Organs or body parts whose underlying similarity arises from their bodies being derived from a common ancestral structure.
ex. wing of bird and arm of human
Analogous structure
Similarity in organs or body part comes from their performing a similar function rather than their arising from a common ancestor
histone acetylation
Addition of negatively charged group histones - neutralizes the positive charge of lysine
PROMOTES TRANSCRIPTION
histone methylation
Can either repress or activate gene expression depending on the amino acid targeted.
- Usually represses transcription.
Which part of the cell cycle should the differentiated donor cell be in SCNT?
G1 - so that the cell is NOT dividing.
What phase should the oocyte donor be enucleated?
The enucleation (removal of meiotic spindle with the chromosomes) should occur at metaphase ll.
What was the secret to success in the cloning of monkeys?
an mRNA called Kdm4d was injected into the enucleated egg fused with monkey fetal fibroblasts. This mRNA is translated to form a H3L9 trimethyl demethylase. The trimethyl groups block gene expression… so once the methyl groups are removed - gene expression is then activated!
- Secret: an enzyme that demethylates histone 3 at lysine 9
Do methyl groups on histones normally repress or activate gene expression?
Normally repress - condense the chromatin
Do acetyl groups on histones normally repress or activate gene expression?
Acetyl groups loosen nucleosome packing - activate gene expression.