Molecular Embryology II Flashcards
Why are humans so smart?
We do not have more genes, but we make the most out of the same genes
What is somite formation controlled by?
Temporal expression of regulatory genes (like C-hairy-I in chicken embryo)
What is the conclusion about segmentation in Drosophila?
One gene many independent controls (i.e. Eve gene segmentation) – different
combination of transcription factors result in a decision to transcribe or not transcribe the
eve gene
Describe generation of diversity by lateral inhibition
Initially, all cells are equal and every cell tries to inhibit its neighbors. Eventually, one
cell gains an upper hand in inhibiting its neighbors. Now, two distinct cell lineages are
formed
In the formation of nervous system, the default pathway is production of neurons.
Which proteins compete for formation of neurons?
Delta and notch. When truncated/mutated delta mRNA is injected, more neurons are
formed and less supporting cells are formed. Thus, notch promotes neuron formation while
delta regulates more glial cell formation.
The process responsible for formation of somites in human is:
Expression of regulatory proteins in a temporally cyclic manner
_______ are responsible for sensory on the dorsal side and motor neurons on the ventral
side of our vertebral column.
Morphogen gradients
Discuss Isotretinoin (Accutane). What does it alter? What are the disadvantages?
After treatment with Isotretinoin, ACNE goes away in ~ 90% of patients. Accutane is
structurally related to retinoic acid which alters gene expression. These medications (like steroids) alter morphogen gradients during critical periods of development.
DISADVANTAGES: Isotretinoin can cause birth defects in the developing fetus of a
pregnant woman. It is important that women of childbearing age are not pregnant and do
not get pregnant while taking this medicine. Women must use two separate forms of birth
control at the same time.
What is chemotaxis? Discuss in terms of neutrophils?
Chemotaxis is cell movement in response to a chemical signal. Movement of a neutrophil
towards a chemical signal formyl-Met – Leu – Phe. Only bacterial proteins contain formylmethionine
and neutrophils can distinguish 1% difference in cconcentration of this peptide
on one side of the neutrophil vs. the other side.
Which protein affects neurite outgrowth and is also essential for the survival of
neurons?
Nerve Growth Factor (NGF)
True or false. Axons create new routes for themselves.
False. Axons follow preexisting routes determined by factors.
What accounts for left-right asymmetry?
Helical beating of cilia at the node involves the dynein motor. The cilia direct flow of
extracellular fluid containing signal proteins to one side. This accounts for left-right
asymmetry (the same dynein motor is responsible for sperm motility. Infertile men with
(with defects in dynein motor) have situs inversus in 50% cases)
In humans, left-right asymmetry is determined by what mechanism?
Helical beating of cilia at the node containing a dynein motor that direct signal proteins
to one side.
What are the four essential processes by which multicellular organism is made of?
(1) cell proliferation (2) cell specialization (3) cell interaction (4) cell movement
Why and how one of X chromosomes in females is inactivated?
In addition to methylation of DNA and histones, an RNA made from X inactivation
center coats the inactive X chromosome
Why human cells (neutrophils) migrate toward peptides containing formyl-methionine?
human neutrophils have receptors for peptides containing formyl-methionine.
Activation of these receptors results in chemotaxis towards the site of bacterial infection.
Similar mechanism activated by specific signals is used for cell movement(s) during
development.
Know what is lateral inhibition and why introduction of truncated delta protein results
in overproduction of neurons.
Lateral inhibition involves cell-cell communication. Initially, all cells are equal and
every cell tries to inhibit (influence) its neighbors. Eventually, one cell gains an upper hand
in inhibiting (influencing) its neighbors.
Now, two distinct cell lineages are formed.
Know why defects in dynein motor results in situs inversus in humans
Helical beating of celia at the node involves the dynein motor. The celia direct flow of
extracellular fluid containing signal proteins to one side. This accounts for left-right
asymmetry. The same dynein motor makes sperm highly motile.
Know the contributions from father and mother to form the zygote
One set of chromosomes, all cytoplasm including mitochondrial DNA is contributed by
by the mother; sperm contributes one set of chromosomes and a centriole
How does alternate splicing in cadherin pre-mRNA helps in new type of tissue
organization?
Cadherin pre-mRNA has 15 different variable regions on separate Exons. Each
cadherin mRNA is a product of one of these variable regions connected to constant region.
Cells containing different cadherins assemble together to form separate tissues.
Know that many genes in higher eukaryotes have multiple control elements (DNA
sequences) that independently regulate gene expression. Give an example.
Eve gene in Drosophila that is involved in segmentation
How are somites formed?
Concentration of a critical factor(s) oscillates temporally. Cells arrested at high (peak)
concentration of this factor(s) form somites. Cells arrested at low (trough) concentration
are between two somites. One gene identified in chicken that cycles is c-hairy-1.
What is a significant function of miRNAs?
miRNAs have several different functions, but one of them is is that they can go back to
the nucleus, bind to the regulatory regions by triple helix formation and direct methylation
of those genes. as differentiation is going on, making more miRNAs that are different, which set up a methylation process and cells keep on differentiating. program at molecular level driven by RNAs and then by methylation
