Molecular Embryology I Flashcards
What is an ectopic pregnancy? What is the most common place it occurs? What is the
frequency of ectopic pregnancies?
Abnormal site of implantation. Vast majority of ectopic pregnancies occur in uterine
tube – tubal pregnancy. 1-2% of all pregnancies are ectopic
Are studies carried out in mouse relevant to humans? Give an example
Human and mouse: similar genes and similar development. A mutation in kit gene
(required for development and maintenance of pigment cells), leads to similar white
patches on their foreheads.
Give two examples of studies carried out in lower eukaryotes, making it relevant to
humans.
Fruit fly gene (Engrailed-I) works fine in mouse. Pax-6 controls eye development and
Pax-6 from other species can grow in Drosophila fruit fly
In most cases, ________ are interchangeable between species; _______ are less
interchangeable
genes (coding regions); regulatory regions
Without survival signals, cells die. What is a survival signal for muscle? And what are
general cell signals?
ACh. General cell signals – survival, differentiation, division
What is the molecular nature of factors responsible for differentiation? How does this
relate to cancer cells?
Protein factors, peptides, fatty acids, thyroid hormone, etc. cause cell differentiation.
Differentiation is specialization and dedifferentiation (back towards embryo). Cancer cells
invariably dedifferentiate and express many embryonic genes.
What is the origin of embryonic stem cells? From which tissue can embryonic stem cells
be obtained?
Blastocyst (early embryo)
What are the four essential processes by which a multicellular organism is made of?
cell proliferation, cell specialization, cell interaction, cell movement
What are exceptions to ‘most human cells have all the DNA intact’?
RBCs, T & B lymphocytes, etc.
Give an example of how during development, a different subset of genes is inactivated in
different issues.
Liver has methylation in controlled region of insulin, resulting in inactive insulin.
However, albumin gene is active. Pancrease has methylation in controlled region of albumin, but has an active insulin gene
Why do bacteria use methylation strategy?
To protect their DNA from restriction endonucleases
Methylation pattern in DNA can be inherited. How does this process work?
Methylated DNA -> DNA replication -> Hemimethylated DNA -> (fully) methylated
DNA
During mitosis and meiosis, most _______ are removed.
DNA methylations. Sperm and egg DNA is not methylated and virtually all genes are
active at fertilization. Exception = imprinted genes
What is imprinting?
Humans have two copies of each gene (except in males, XY).
In few cases (about 80 genes), only one of the genes is expressed. This is because of GC
methylations in the imprinted genes on one of the chromosome are left alone / or
methylated very early. Result: one allele on autosomes (maternal or paternal gene) is off.
What is XIC and XIST? What do they act to do?
XIC – X inactivation center. XIST – X inactivation specific transcript (a noncoding
RNA). One of two X chromosomes in females randomly gets inactivated.
How is the inactive X chromosome organized?
Transcriptionally inactive structure: heterochromatin
What are two ways of making sister cells different?
Asymmetric division: sister cells born different. Symmetric division: sister cells become
different as result of influences acting on them after birth
Ca2+ concentration in a neuronal cell is high in dendrites, low in the cell body and axon,
and intermediate in between. What’s the concept behind this?
Ions (membrane channels) can distribute asymmetrically, as can proteins and mRNAs
What is gene expression regulated by?
Binding of transcription factors to regulatory regions in DNA. Regulatory DNA
sequences are usually in the 5’ flanking region; they can be in 3’ flanking or also in the
coding region (usually in introns)
Why is DNA bent?
Protein binding often alters DNA shape. Remember how DNA is packaged in
nucleosomes.
A protein heterodimer binds to DNA regulatory region. What class of proteins is this?
Helix-loop-helix (HLH) proteins
What happens with transcription factors with no DNA binding domain as a result of
alternative splicing?
They form inactive heterodimers; no transcription.
Random inactivation of one of the X chromosomes in females is initiated by
X-inactivating non-coding RNA(s)
What are main principles behind triplet repeat diseases?
Autosomal dominant. Triplet repeat diseases happen in the germ line so they are in
inherited. Get worse through successive generations. Longer repeat, more severe disease.
Repeat can be in protein coding region or in 5’ or 3’ UTR
How do cadherins act in embryological development?
Cadherins form homodimers and form tissues from cells expressing same cadherin.
Note E-cadherin in ectoderm, N-cadherin neural tube. Neural crest does not E- or Ncadherin.
How are different cadherin mRNA expressed in different neural tissues
Alternative splicing of cadherin mRNA
What happens when you mix cells expressing different cadherins or different levels of
the same cadherin?
Cell sorting to group similar cadherins
