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54 Cards in this Set
- Front
- Back
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All cells are derived from ??
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The fertilized egg
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How many cells are in an adult human body?
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~ 10 trillion
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What is 'developmental potential'?
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the ability of cells to develop into various cell types, given the right conditions/instructions
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Define the 4 levels of developmental potential.
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1. todipotent - can make all cell types and tissues of the organism AND extraembryonic tissues (ie. fertilized egg)
2. pluripotent - can make all cell types of germ layers, but NOT extraembryonic tissues 3. multipotent - can make several cell types 4. unipotent - can make only 1 cell type |
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Does developmental potential expand or become restricted over the course of embryogenesis?
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Progressively more restriction
decreased potential increased specificity |
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What are the three steps of fate acquisition? Define. Are they reversible or irreversible?
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Specification - cell shows bias towards a particular fate. when cell can differentiate autonomously in a neutral environment. (reversible)
Determination - cell is capable of differentiating autonomously in a non-neutral environment (irreversible) Differentiation - fate-specific changes in structure/function |
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What is autonomous specification? what is conditional specification?
Which one is the predominant mechanism of cell fate acquisition? |
Independent self-differentiating parts vs development depends on interactions with neighboring cells (can be regulated)
Conditional specification - predominant |
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In autonomous specification, what determines cell fate?
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Specific determinants, which are inherited
B/c of asymmetric division, or asymmetric localization of determinants |
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In conditional specification, what determines cell fate?
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Inductive signaling from neighboring
- early embryonic development is regulative: missing cells can be replaced early in embryogenesis |
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What are two potential mechanisms for cell differentiation?
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Differential gene loss
Differential gene expression |
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How is dolly cloned?
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Get donor cell from animal to be cloned, take only nucleus.
Take unfertilized egg cell from other animal, remove its nucleus, and insert other nucleus. Implant embryo into surrogate mother |
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What does the cloning of Dolly show?
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That inactive genes can be reactivated.
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Just because two animals are identical genotypes, why might they not have identical phenotypes (look or behave differently)? (2)
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X-chromosome inactivation
environmental influences |
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Is gene activation/inactivation reversible?
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Yes
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Is there any loss of genetic material during differentiation?
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No
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How many genes are in the human genome?
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~30,000
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How many genes does the typical cell express?
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10,000 - 20,000
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How do you control gene expression in a cell? Name 5 points of regulatory control.
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1. transcription
2. splicing of primary mRNA 3. Export of processed mRNA 4. translation/mRNA half life 5. Post-translational modification |
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What is Waardenburg syndrome Type 1?
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Mutation in Pax3 gene
- white forelock, broad nasal root, hearing losss - due to error in transcriptional regulation defect arising from neural crest cell migration |
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What are some inborn errors in nuclear RNA processing?
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1. mutations in splicing factors
2. Mutations in splice sites |
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What is branchio-oto-renal syndrome? What causes it?
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Caused by mutations in splice acceptor/donor sites - heterozygous mutations in eyes-absent-1
hearing loss, kidney failure (missing 1 kidney), branchial defects, fistulas/cysts in neck Homozygous mutation of eyes-absent-1 = lethal (no kidneys!) |
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What causes Fragile X syndrome?
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Inborn errors in mRNA transcription
- CGG repeat expansion in FMR1 gene prevents transcription (FMR1 protein is required for translation/transport of specific mRNAs in nervous system) So: No FMR1 = no transcription of neuronal proteins = defects in neuronal development |
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What are two patterns of gene expression? Describe.
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1. Spiral patterns - every cell type, tissue specific, organ specific, cell-type specific.
2. Temporal patterns - constitutive. Modulated (Inducible, repressible, rhythmic, circadian) |
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What are DNA regulatory elements?
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General transcription factors
activators (bind to enhancers) repressors (bind to silencers) |
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What is the same/different about DNA in different cells?
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- All cells have the same DNA
- Most RNA pol IIs have the same TFs Diffs: - Diff regualtory proteins (modulate expression of a gene) - specific combinations of activator/repressor proteins (which bind upstream the regulatory sequences) |
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What is the purpose of a signaling gradient?
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cellular diversity (differential gene expression)
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What two things can generate differential gene expression?
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1. Different combinations of regulators
2. Signaling gradient |
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What is epigenetics?
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HERITABLE changes in phenotype/gene expression caused by mechanisms other than underlying changesin the DNA sequence
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Name 3 types of epigenetic modification (not of the DNA sequence itself). Explain the effect of each one.
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1. Histone acetylation - increases DNA accessibility by trsn factors *(deacetylation - decreases DNA accessibility by TFs)
2. DNA methylation of cytosine residues in CpG dinucleotides ==> inactive genes 3. RNA mediated - noncoding and interfering RNAs all of these epigenetic mechanisms control biological processes in genes |
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What is bookmarking?
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epigenetic mechanism of transmitting patterns of gene expression to daughter cells through mitosis. - via patterns of histone modifications
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What is imprinting?
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genes where only 1 allele is expressed in parent-of-origin manner. Either maternal or paternal allele is expressed in the embryo, but not both.
- Methylation |
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What is gene silencing?
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non-genetic inactivation or repression of gene expression
-histone modification, heterochromatin |
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What is reprogramming?
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Remodeling/removal of epigenetic marks
- Methylation |
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What is X-chromosome inactivation?
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Regulation of active X-chromosomes during dosage compensation (one of the 2 x chromosomes in females is silenced)
- methylation, chromatin, RNA |
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What is a Barr body?
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condensed, inactive X-chromosome (in females only) - (other x-chrom is active)
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Klinefelter's syndrome - What are the sex chromosomes? What is the gender appearance? Do the cells have Barr bodies?
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XXY
Male in appearance Yes |
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Turner's syndrome - What are the sex chromosomes? What is the gender appearance? Do the cells have Barr bodies?
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XO
female no |
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What if you have 3 X's (XXX) - how many barr bodies in each cell?
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2
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Where is the inactive X chromsome located?
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near the nuclear periphery
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What is the structure of the inactive X-chrom?
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-packaged with hypo-acetylated histones
-has islands of methylated cPg's at 5' ends -has silenced genes -associated with Xist-RNA (a noncoding RNA) |
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At what stage does the cell inactivate all but 1 X chromosome?
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200 cell stage of embryogenesis
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How is it determined which X chromosome will be inactivated?
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Randomly.
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Are all the genes silenced on the inactive X-chromosome?
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No, some remain active
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Give an example of X-chromosome inactivation
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calico cats (only females can have the calico pattern)
O= orange, o=black O isi x-linked Males can be O (orange) or o (black). Females can be OO (orange), oo (black), or Oo (calico) |
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Where can you find pluripotent cells?
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Inner cell mass
Stem cells |
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Can cells cross germ layer? Ie. mesoderm cells become endoderm cells
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Usually no - stem cells are the exception though
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For the most part, is mammalian development regulative or not? What's the exception?
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Regulative
Stem cells |
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Is the inner cell mass pluripotent or todipotent?
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Pluripotent
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What does it mean that conditional specification has the capacity for regulative development?
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that early in embryogenesis, missing cells can be replaced
later stage embryos are less regulative. |
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What mammalian cells are NOT regulative?
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Stem cells.
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how does preimplantation genetics show that mammalian development is regulative?
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pluck out a few blastomeres from an early blastocyst. Do genetic testing. Blastocyst still develops fine, not missing anything.
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What are the 4 genes that, if you put it back into a cell, you could convert it back into a stem cell?
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iPS, iPSCs
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What happens if there's a mutation in the splice site in nuclear RNA?
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Then it splices at the cryptic splice sequence, which is usually out of frame...so a some intron included.
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What gives general TFs specificity?
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Activators (enhancer binding proteins), Repressors (silencer binding proteins)
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