Cell Signalling Flashcards
During the process of embryonic development, undifferentiated precursor cells differentiate and organize into …
The complex structures found in functional adult tissues
The intricate process of embryonic development requires cells to…
Proliferate, differentiate, and migrate to determine the final size and shape of the developing organs
Disruption of signalling pathways can result in
Human developmental disorders and birth defects
Cell signalling is part of a complex system of communication that governs
Basic cellular activities and coordinates cell actions
Signal transduction
Any process by which a cell converts one kind of signal or stimulus into another
Many enzymes are switches “on” or “off” by
Phosphorylation and de phosphorylation
6 types of cell changes from zygote to human
- Proliferation (mitosis)
- Differentiation (daughter cells are not same as precursor)
- Migration (blood cells)
- Growth
- Transformation (change to serve other function)
- Death (apoptosis)
Can a somatic skin cell become a human
No, it is not potent. Zygote has potency meaning it is not so differentiated good one specific function.
Totipotent
Cells that have high potential to grow to a human (zygote)
All of the 6 types of cell changes are caused by
Cell signalling
Transcription factors
Factors or proteins that affect transcription by binding to DNA and cause up or down regulation of genes.
Protein modification and types
Addition or removal of chemical molecules from proteins
Cotranslational protein modification: protein mod during translation
Post translational: protein mod after translation (phosphorylation and de phosphorylation)
Amino acid structure
Contains an N terminis and a C terminis. N is our first and starts with MET (start codon) but is cleaved off in protein modification.
Which amino acid phosphorylation by protein kinase
Ser, thr, Tyr
What protein removes phosphates
Phosphatases
Kinases add phosphsate from
ATP
Protein kinases can be ….
Tyrosine kinases= receptor tyrosine kinase(RTK)(receptors on cell membrane) or non receptor tyrosine kinases (in cytoplasm or nucleus)
Or
Serine/Therein kinases
Conformational change
3D structure of protein changes by adding a chemical or molecule
Protein domains
Extracellular
Transmembrane
Intracellular
Conformational change process (basic)
Conformational change goes through protein domains, expose site, activated receptor and recruits target protein, stimulates A and activates A, then B, then C, then activation of TF, then translocation to nucleus, then regulates gene expression.
Types of intracellular signalling
Autocrine: signalling molecule produced by cell with receptor for it
Paracrine: cells in Visconti’s of signalling cell have receptors
Endocrine: signals move through body fluids to any tissue site with cells with receptors
During embryogenesis the differentiation of many different cell types is regulated through a relatively restricted set of molecular signalling pathways:
- morphogens
- notch/ delta
- transcription factors
- receptor tyrosine kinases (RTK)
Two classes of proteins required for intercellular communication are
Gap junctions and cell adhesion molecules
Gap junctions
Means for cells to directly communicate to each other
- Gap junction intercellular communication
- pore sized only allowing smaller molecules like ATP and ions
- important for regionalization
Gap junctions are made up of
6 Connexon Hemi channels
-each has 4 transmembrane domains with the N and C terminus in the cytoplasm
Cell adhesion molecules
Adhere cells
- have large extracellular cadherin domain that interact with extracellular matrix and other extracellular domains of other cells.
- critical to regulate cell layers (endothelial and epidermal separation) and regulate cell migration, and neuron growth
Extracellular Cadherin domain connected by
Calcium binding site
Cytoplasmic domain of cadherin has what proteins
P120, Beta- catenin, alpha catenin and actin cytoskeleton
Yep types of cell adhesion molecules
Cadherin and immunoglobins
Example of immunoglobin superfamily
Neural cell adhesion molecule
Morphogens and examples
Diffusible molecules that specify which cell type will be generated at a specific anatomic location and direct the migration of cells and their processes to their final destination
Retinoids acid, transforming growth factor beta (TGF-B)/bone morphogenetic proteins (BMPS) and the hedgehog and Wnt protein families
Retinoic acid
Excessive amount causes
The anterior (rostral, head)/ posterior (caudal, tail) or anteroposterior (AP) axis of the embryo is crucial for determining the correct location for structures such as limbs and for the patterning of the nervous system
Retinoic acid posteriorizes the body plan. Therefore excessive or inhibition of its degradation leads to truncated body axis where structures have a more posterior nature
Metabolizes vitamin A
Insufficient retinoic acid or defects the enzymes such as retinal aldehyde dehydrogenase will lead to
A more anteriorized structure
At a molecular level, retinoic acid binds to its receptors ________ the cell and _____ them
Inside
Activates them
Retinoic acid receptors are
Transcription factors and therefore their activation will regulate the expression of downstream genes such as HOX genes
Dietary vitamin A (retinol) metabolism
Retinol becomes retinal from retinol dehydrogenase. Retinal becomes retinoic acid from retinal dehydrogenase. (Oxidation reaction) Retinoic acid becomes inactive metabolites from CYP26
Cellular retinal binding proteins and cellular retinoic acid binding proteins can inhibit such reactions.
6 regulators of retinoic acid
- Intake
- Retinol dehydrogenase
- Cellular retinal binding proteins
- Retinal dehydrogenase
- Cellular retinoic acid binding protein
- CYP26
Mutations in any can cause changes in embryologically development but process is highly regulated
Transforming Growth Factor beta/BMP
Members of the TGF-beta superfamily include TGF-beta, BMP’s, activin and nodal.
These molecules contribute to the establishment of dorsiventral patterning, cell fate decisions, and formation of specific organs, including the nervous system, kidneys, skeleton, and blood.
In humans there are 3 TGF-beta idk forms
TGF-beta 1, TGF-beta 2 and TGF-beta 3
TGF-beta pathway A
The type 2 TGG-beta receptor subunit or TbetaR|| is most likely active
TGF-beta pathway B
On binding of ligand TGF-beta to TbetaR-||, a type 1 receptor subunit is recruited to form a heterodimeric receptor complex, and the TbetR-| kinase domain is transphosphorylated (-p). Signalling from the activated receptor complex phosphorylates R-SMAD’s, which then bind to a co-SMAD, then translocates from the cytoplasm to the nucleus and activated gene transcription with cofactors.
Sonic hedgehog (Shh) primary receptor and absence/ presence of shh
Primary receptor for shh is Patched (PTCH), a 12- transmembrane domain protein that, in the absence of shh, inhibits smoothened (Smo), a seven-transmembrane domain G protein linked protein, and downstream signalling to the nucleus
In the presence of Shh, Ptc inhibition is blocked and downstream events follow, including nuclear translocation of Gli, with transcriptional activation of target genes, such as Ptc-1, Engrailed and others.
Shh and BMP’s are expressed in __________ gradients in the developing ____ tube
Opposite
Neural
Moving from dorsal to ventral there is a growing gradient of Shh. Moving from ventral to dorsal, there is a growing gradient of BMP’s
At any anatomical location of neural tube, there are different levels of Shh and BMP’s and therefore differentiates regions and cells.
The gradients determine dorsal-ventral cell fates
In the neural tube, Shh is secreted by the…… and BMP’s (Bone morphogenetic proteins) are secreted by the…
Notochord and floorplate
Roofplate and overlying epidermis
Wnt/beta-Catenin
The Wnt-secreted glycoproteins are vertebrate orthologs of the Drosophila gene Wingless (if mutated flies don’t develop wings)
The 19 Wnt family members control several processes during development including establishment of cell polarity, proliferation, apoptosis, cell date specification, and migration
Receptor of Wnt’s
Specific Wnts’s being to one of10 different Frizzled (Fzd) 7 transmembrane domain cell surface receptors, and with low density lipoprotein receptor-related-protein (LRP5/6) co receptors, thereby activating downstream intracellular signalling events.
Wnt/beta-catenin pathway
A) in absence of Wnt ligand binding to Fzd receptor, beta-catenin is phosphorylated by a multi protein complex (axin, GSK-3, APC) and targeted for degradation. GSK-3 is not phosphorylated. Target gene expression is repressed (inhibited) by T-cell factor (TCF).
B) When Wnt binds to Fzd, LRP core rotors are recruited, Dishevelled (DVL) is phosphorylated and activates to phosphorylated GSK-3 making it inactive and beta-catenin then accumulates in the cytoplasm. Some beta-catenin enters the nucleus to activate target gene transcription.
NOTCH-DELTA Pathway purpose
This pathway often specifies which cell fate precursor cells will adopt
Integral for cell fate determination, including maintainable of stem-cell niches, proliferation, apoptosis and differentiation
Ligand-receptor binding triggers proteolytic events (protein breakage) leading to the release of the NOTCH intracellular domain (NICD). When the NICD translocates to the nucleus, a series of intranuclear events culminated in the induction of expression of hairy-enhancer of split, an HLH transcription factor that maintains the progenitor state by repressing pro neural basis HLH genes
Proteases and peptidases cleavage
Cut into small pieces
Cut at specific place
Domains of NOTCH receptor
NECD
NTMD
NICD
Differentiating cell
Progenitor cell
Cells already on path to be a particular cell
Stem cells with high potency to be something
NOTCH/Delta signalling pathway
Differentiating cell is signalling cell with its ligand DELTA/Jagged which can bind to NOTCH. In progenitor cells, activation of NOTCH signaling leads to cleavage of the NICD. NICD translocates to the nucleus, binds to a transcriptional complex, and activates target genes such as Hes1, that inhibit differentiation.
Binds, exposes site where ADAM can cleave ECD, so change in conformation so presenilin cleave TMD so NICD can move to nucleus
NOTCH has different _____ sites
Cleavage
If Delta/Jagged bind to protein it alters confirmation and exposes cleave site so ADAM can cleave protein in extracellular space. Presenilin can cleave in transmembrane domain, and Furin can cleave intracellular.
Transcription Factors
Belong to a large class of proteins that regulate the expression of many target genes, either through activation or repression mechanisms .
-will bind to specific nucleotide sequences in the promoter/ enhancer regions of target genes and regulate the rate of transcription of its target genes via interacting with accessory proteins
Transcription complex
Transcription factor+target genes+accessory proteins
Histones and his tone modification
Positively charged nuclear proteins around which genomic DNA is cooked in units to tightly pack it in Structures known as nucleus ones within the nucleus
Histone modification is used by TF to regulate activity of their target promoters. Ex: phosphorylation, acetylation and methylation
DNA is less tightly bound to _____ histones
Acetylated, allowing more access of TF and other proteins to the promoters on target genes
TF can modify Histone acetylatioj by recruiting Histone acetyltransferases or Histone deacetylases.
HAT’s
Histone acetyltransferases
Controls Histone acetylation status
can add acetyl groups
HDAC’s
Histone deacetylases can remove acetyl groups
Phosphorylation of histones leads to
Opening of the chromatic structure and activation of gene transcription
Epigenetic modifications alter the transcriptional properties of chromatin pathways
A) in areas of transcriptionally inactive chromatin, the DNA is tightly bound to the histone cores. The histones are not acetylated or phosphorylated. HDAC’s are active and HAT’s and histone kinases are inactive. (Highly methylated which suppress gene expression)
B) in areas of transcriptionally active chromatin, the DNA is not tightly bound to the histone core, and the DNA is unmethylated. The histone proteins are acetylated and phosphorylated. HDAC’s are inactive and HAT’s and histone kinases are active
Transcription factor examples
- HOX proteins (mutations in the DNA-BD of the NKX2-5 cardiac defects)
- PAX genes (ophthalmic defects)
- Basic Helix-Loop-Helix TF (muscle differentiation)
Receptor Tyrosine Kinases (RTKs)
Many growth factors signal by binding to and activating membrane bound RTKs. These kinases are essential for the regulation of cellular proliferation, apoptosis, and migration as well as processes such as the growth of new blood vessels and axonal processes in the nervous system.
Receptor tyrosine Kinase signalling pathways
A) in absence of ligand, the receptors are monomers and are inactive.
B) on binding of ligand (double) the receptors dimerize (bind together) (ligand-mediated dimerization) and trans phosphorylation occurs, which activates downstream signalling cascades.
Two single ligands can bind to two RTKs and can a conformational change that causes the two RTK’s to have affinity for each-other and cause receptor mediated dimerization
Mesodermal cells upon activation of RTK
Brings mesodermal cells that differentiate together and outer areas become epithelial and inner become blood cells making up an early circulatory system!
Stem cell differentiation
Adult or embryonic stem cells can divide symmetrically, giving rise to two equivalent daughter stem cells (vertical division) or asymmetrically, giving rise to a daughter stem cell and a nervous system progenitor cell (horizontal division)
Stem cells and induced pluripotent stem cells (IPS) have the capacity for___
Self renewal, cell death, and becoming progenitors.
- progenitor cells have a limited ability for self renewal but can differentiate into various cell types or undergo cell death
- adult differentiated somatic cells, such as skin fibroblasts, can be reprogrammed into IPS with the introduction of the master transcription factors SOX2, OCT3/4 or KLF4.
IPS
Induced pluripotent stem cells
- develop week 3 when germ layers or defined.
- are 3 types of IPS- ectoderm, endoderm and mesoderm. Each stem cell can make all the cells of its germ layer.
Totipotent
Pluripotent
Multi potent
Zygote (can make all cells)
IPS (can make many cells)
Can make few cell types (adult bone marrow, skin etc.
Vitamin A caused birth defects/ diseases due to abnormal signalling
CNS: spina bifida
Eyes: anopthalmia
Face: cleft palate, harelip
Ear: accessory ears
Urogenital system: cryptorchidism, ectopic ovaries
Heart: aortic arch defects, incomplete ventricular separation
TGF-beta family caused birth defects/ diseases due to abnormal signalling
Affects nervous system, kidneys, skeleton and blood
Hedgehog caused birth defects/ diseases due to abnormal signalling
Brain defect: holoprosencephaly, Pallister syndrome, Gorlins Syndrome
Wnt/beta-Catenin pathway caused birth defects/ diseases due to abnormal signalling
Williams-Beuron sundrome
Osteoporosis-pseudoglioma syndrome
Notch-Delta pathway caused birth defects/ diseases due to abnormal signalling
Alagille syndrome, CASASIL
Transcription factors caused birth defects/ diseases due to abnormal signalling
Disorders of chromatin remodelling: Rett, Rubinstein-tayabi, alpha-thalassemia/X-linked mental retardation
Homeobox proteins caused birth defects/ diseases due to abnormal signalling
Cardiac atrial-septal defects and lissencephaly syndrome
Pax gene caused birth defects/ diseases due to abnormal signalling
Occular defects, alveolar rhabomyosarcoma, waardens syndrome
Receptor Tyrosine Kinase caused birth defects/ diseases due to abnormal signalling
Milroy disease, cancer
MET VS EMT in adhesion molecules
More adhesion
Less adhesion
______ posteriorizes body and specifies heart tube dilations
Retionic acid
Examples of RTK
VEGF, IGFR, EGFR, RET, MET
FGF8 specifies which body side
LEFT
Microglial and macroglial cells are derived from?
Mesoderm
Ectoderm
