Developmental Genetics and Pharmacogenetics'

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Developmental Genetics and Pharmacogenetics.

• SF 33 Genetics 5
• R. Daniel Gietz Ph.D.
• Dept or Biochemistry and Medical Genetics

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Learning objectives

• After this lecture the student should be able to
• Define the basic concepts of Pattern formation.
• Describe how transcription factors, signaling
  molecules and Growth factor receptors influence
  human development.
• Give an example of a birth defect caused by
  disruption of pattern formation.
• List the 5 data types used in the field of
  Pharmacogenetics.
• Give an example of a genetic condition that shows
  variability in genotype and drug sensitivity.

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Developmental Genetics

• Birth defects are the most common cause of infant
  death in the USA.
• 100,000 children born in the USA each year with
  a birth defect.
• defined as an isolated abnormality or they can be
  one of the more than 2000 genetic syndromes.
• etiology is unknown however it is estimated that
  a large portion of the caused by mutations in
  genes that control normal development.

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Basic Concepts

• model systems
• D. melanogaster (fruit fly)
• X. laevis (African clawed frog)
• D. rerio (zebrafish)
• C. elegans (nematode),
• G. gallus (chicken),
• M. musculus (mouse),
• P. hamadryas (baboon).

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Model Systems
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Model systems are useful for experimentation Muta
genesis screens can be carried out and a large
number of offspring can be analyzed for
abnormalities in embryonic development. Genes
can be mapped and cloned. Many of the genes
identified are evolutionarily conserved. Many of
the genes identified in Drosophila melanogaster
are utilized through out the animal kingdom to
establish the body plan during development.
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Concepts in Modern Developmental Biology

• Morphogenesis ..process of changes in cell shape,
  adhesion, movement, proliferation or cell death
  to give a 3 dimensional structure.
• Differentiation is the process by which one or
  more clles acquire a specific pattern of gene and
  protein expression characterized by a cell type
  or tissue.

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Concepts in Modern Developmental Biology

• Fate is the quality of a specific region of an
  embryo that will develop the same or similar
  structures.
• Different regions of the embryo are described as
  a fate map.
• The process by which a cell achieves its fate is
  called a developmental program.

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Concepts in Modern Developmental Biology

• A region of an embryo is said to be pluripotent
  if it can give raise to multiple structures.
• During embryonic development embryonic regions
  become committed to their fate in a two stage
  process of specification followed by
  determination.
• Specification is labile determination is not

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Concepts in Modern Developmental Biology

• A cell lineage are the progeny of a particular
  cell. Cells that remain physically adjacent are
  referred to as clones.
• Cells can have either lineage or position
  dependent development or in other terms cell
  autonomous (not affected by position) or cell
  nonautonomous (affected by position) development.

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Concepts in Modern Developmental Biology

• Embryonic induction is the process that
  determines the fate of one embryonic region after
  receiving a signal from another region.
• Regulative development is defined by the
  compensation for removal of certain embryonic
  structures by others.
• Mosaic development describes the process of
  development of different regions that are
  independent of each other.. Embryonic
  development goes from regulative to mosaic.

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Figure 17-1
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Genes involved in Development

• The genes required for normal development encode
  many different types of products. These include
  signal transduction molecules such as growth
  factors and their receptors, DNA transcription
  factors, components of the extracellular matrix,
  enzymes, transport systems and other proteins.
  Some examples are given in Table 17-1.

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Human developmental abnormalities
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Homologue of Drosophila developmental control
genes
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Early Development

• Early development is well understood
• Due to experiments on mice
• First cells to differentiate are those that give
  rise to extraembryonic tissues required for
  implantation and formation of the placenta
• See figure 17-3

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Fig 17-3
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Early mammalian development

• Early development is regulative.
• a portion of the embryo can be lost or removed
  and is still able to develop normally
• Any cell from the ICM can be removed in the first
  2 weeks via biopsy due to regulative development.
  Low risk of birth defects in first two weeks.

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Early Mammalian development

• Mosaic development refers to when the fate of a
  cell is specified independently from its
  environment.
• If something is removed or destroyed what remains
  does not compensate
• Teratogenic damage during this form of
  development causes harmful effects to fetal
  cells.
• Gastrulation is a critical part of development
  marks the beginning of the period when the embryo
  cannot easily compensate for losses or damage.
• Several organ primordia are allocated from small
  numbers of cells organogenesis is sensitive to
  defects

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Gene expression and Development

• How do cells that are identical genetically form
  complex adult organisms composed of many
  different cell types and tissues?
• What controls the fate of a single cell, making a
  cell differentiate into a brain or liver cell?
• How do cells organize into discrete tissues?
• How is the body plan of the organism determined?

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Gene expression development

• Most genes are house keeping genes
• Some are specialty genes that define unique
  features of different cells.
• Its the different combinations of genes that
  define each cell type.
• Many single gene defects have pleiotropic effects
  due to the many different processes they are
  involved with.

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Genetic Mediators of Development

• CBP or Creb Binding protein is an important
  protein for transcription regulation.
• Is a molecular bridge or co-activator in several
  types of tissues. See Figure 17-4A.
• Loss of function causes a Dominant mutation

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Fig 17-4A
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Pleiotropic mutation

• Rubenstein-Taybi syndrome
• Caused by loss of function of the CBP or Creb
  Binding Protein causes a dominant mutation.
• Phenotype is mental retardation with broad thumbs
  and toes accompanies by hirsutism, cyptorchidism,
  congentical heart defect and characteristic
  facial features with down slanting palpebral
  fissures and hypoplastic maxilla and a prominent
  nose see Fig 17-4B.

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Fig 17-4B
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Cell lineage

• Once differentiated the phenotype of a cell is
  usually stable thru subsequent divisions
  establishing a cell line.
• Certain cell lineages require replacement such as
  erythrocytes and platelets and depend on stem
  cells.
• Stem cells are said to be pluripotent
• See Figure 17-5

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Figure 17-5
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Cell Fate

• What are the genetic mechanisms that account for
  progressive specification and determination of
  cell fate during development?
• Not fully understood
• Models indicate that tissue specific
  transcription factors act in a hierarchical and
  combinatorial networks to specify cell fates
• Waardenburg syndrome (PAX3) Figure 17-6.

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Fig 17-6 A
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Fig 17-6B
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HOX Genes

• Hox genes were discovered in D. melanogaster
• Homeodomain proteins that bind DNA
• Organized in gene clusters
• See Figure 17-7

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Figure 17-7
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HOX mutations

• Hox gene mutations in mice have been shown to
  produce homeotic transformation of vertebral or
  spinal segments.
• HOX13 mutations cause synpolydactyly
• Semidominant causing interphalangeal webbing and
  extra digits in hands and feet.
• Figure 17-8

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Figure 17-8
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Paracrine Factors in Development

• Work in a cell non autonomous fashion
• Are secreted from cells and elecit a simple on or
  off switch or multiple responses due to the
  concentration gradient.
• Paracrine Signalling Molecules (Morphogens)
• 1.Fibroblast growth factors family (FGF FGFRs)
  19 different FGFs,.
• 2.Hedgehog family (First discovered in the Fly)
• 3.Wingless (Wnt) family (also discovered in the
  fly)
• 4.Transforming Growth Factor B family (TGF-?)

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Genetic Mediators of Development
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Genetic Mediators of Development

• Hedgehog family
• D. melanogaster, vertebrates have Sonic hedgehog,
  (Shh). Receptor is patched
• Shh binds to patched suppresses transcription of
  the TGF-? and Wnt genes causing cell growth
  inhibition.
• Mutation is the human homologue PATCHED (PTC)
  causes Gorlin syndrome,
• rib defects, cysts of the jaw and basal cell
  carcinoma.

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Figure 17-10
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Genetic Mediators of Development

• Wnt family
• D. melanogaster with homologues in vertebrates
• glycoproteins
• polarity of the limb for the dorso/vental axis.
  The participate in brain, muscle, gonads and
  kidney development.

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Genetic Mediators of Development

• TGF-? family
• large group of genes that produce proteins that
  form homo and heterodimers.
• act in bone formation pathway as well other
  morphogenetic pathways.
• Mutations in CDMP1 (cartilage-derived
  morphogenetic protein 1) cause various skeletal
  abnormalities.

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Extracellular Matrix proteins

• serve as scaffolding for all tissues and organs.
• collagens, Fibrillins, proteoglycans, and large
  glycoproteins such as fibronectin, laminin, and
  tenascin.
• fibrillin-1 - Marfan syndrome
• elastin supravalvular aortic stenoisis,

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Pharmacogenetics.
One Size Doesnt Fit All
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What is it?

• It is well known everyone does not respond to
  medication the same way
• Environment, diet, state of health influence
• Genes also play a critical role
• Pharmacogenetics is the study of how genes affect
  the way people respond to medication
• Goal is to tailor medicines to peoples unique
  genetic make ups.

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Pharmacogenetics

• the process would include genetic profiling of
  each patient by their physician
• "personalize" their medicine to treat medical
  problems that may effect them in the future
• The potential benefits of this are decreased
  adverse reaction to particular drugs.

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www.pharmgkb.org
Glossary of Pharmacogenetic Terms
Pharmacodynamics study of the relationship
between drug concentration and it site of action
and magnitude of effect Pharmacokinetics study
of bodily adsorption, distribution metabolism,
and drug excretion. Drug Chemical or biological
substance used in diagnosis, treatment or
prevention of a disease of phenotype. Molecular
Assay a test which measures a characteristic of
a molecule. Cellular Assay a test which
measures characteristics of a cell. Genotype The
genetic makeup of an individual. Phenotype
Observable characteristics of an individual.
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www.pharmgkb.org
Data important for the field of Pharmacogenetics
1.Clinical outcome variable response to drugs
can cause measureable differences in clinical
endpoints cure, morbidity side effects and
death. 2.Pharmacodynamic and drug response
Genetic variation in drug Targets can cause
measurable response to a drug. Data in this
category document biological and physiological
response. Variation is measured at the whole
organism level. 3.Pharmacokinetics genetic
variation in absorption, distribution
and Metabolism or elimination results in changes
in drug availability. Looks for genetic
variation that leads to variation in drug
levels.
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www.pharmgkb.org
Data important for the field of Pharmacogenetics
4.Molecular and cellular Functional Assays
genetic variation can alter these tests and this
may correlate with the organisms variation
in drug response. 5.Genotype Collection of
alleles carried by the organism.
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168 variant genes, 417 drugs, 35 pathways, 333
diseases 108 phenotypes.
Some examples Breast cancer therapy some
individuals with a specific genetic Variation in
an enzyme called CYP2D6 do to respond well to
Tamoxifen a common breast cancer drug. Blood
Thinner Dosing differences in the gene VKORC1
Influence how much warfarin is optimal for each
person. This has Lead to faster and more precise
dosing.
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Glucose 6-phosphate dehydrogenase (G6PD)
deficiency

• clinical expression of G6PD variants encompasses
  a spectrum of hemolytic syndromes
• Affected patients are usually asymptomatic,
• patients have episodic anemia
• severe hemolysis after exposure to drugs
  (including the antimalarial drug primaquine and
  certain sulfa drugs) or to fava beans

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Malignant Hyperthermia

• is a lifethreatening, acute pharmacogenetic
  disorder, developing during or after a general
  anaesthesia
• Chloroform, Ether, Halothane, Enflurane,
  Isoflurane, Sevoflurane, Deflurane
• Some MH families showed a defect on chromosome
  19, in the ryanodinereceptor

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Porphyria

• disorder in which the body produces too much of
  the chemical porphyrin.
• cause chest pain, abdominal pain, muscle cramps,
  weakness, hallucinations, seizures,
  purple-red-colored urine, or mental disorders
  like depression, anxiety, and paranoia
• Attacks of the disease can be triggered by drugs
  (barbiturates, tranquilizers, birth control
  pills, sedatives), chemicals, certain foods, and
  exposure to the sun.

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Conclusions

• Research into Pharmacogenetics will make the drug
  a physcian prescribes more effective and safer.
• The HGP will aid in the identification of human
  genetic variation involved in variable drug
  responses.