Developmental Genetics

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Developmental Genetics
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Developmental Genetics

• Topics
• I. Genetic Basis of Differentiation
• II. Control of Gene Expression in
• Differentiation
• III. Nature of Determination

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Development ??? organism

• ????????????? Single fertilized egg cell ????
  embryo ????????? adult
• Adult ?????????? cells ????????? trillions (1012)
  
• ??????????????????????? organs ???? ?
• Organ ?????????? tissues ????????? ?
  ???????????????????????????????
• Tissue ??? ?????????????????????????
  ???????????????

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• Cell Differentiation

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• Embryonic development ??? Amphioxus

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Differentiation

• ????????????? ?????????????? (specialized
  characteristics) ???????? type ???? ?
• Specialized cellular functions ???????
• 1) Proteins structural proteins for cell
  shapes
• 2) Enzymes specific chemical reactions
• 3) Hormones signals from cell to cell

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Genetics ??? Developmental Pathway

• ????????? ???? Mutation
• Developmental pathway ?????????????????????
  differentiation
• ????????????????????? tissues ??? organs
  ????????? Phenotypes ??? differentiated cells

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• ????????????? Developmental pathway
• Different gene products
• Signal molecules signal receptors
• Cytoplasmic proteins signal transducers
• Transcription factors
• Regulator proteins

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I. Genetic Basis of Differentiation
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I. Genetic Basis of Differentiation

• 1. Theory of development
• 1.1 Theory of Mosaic Development
• 1.2 Theory of Regulative Development
• 2. Substances of development
• 2.1 Determinants
• 2.2 Inducers
• 2.3 Morphogens

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Genetic Basis ??? Cell Differentiation

• Early embryonic cells ?????????????????????
  ?????????????????
• Differentiated cells ???? specialized products
  2 ?????????
• 1) Fundamental proteins ????????? (vital)
  ???????????
• Housekeeping genes RNA polymerases
• ribosomal proteins
• 2) Specialized cell products ????????? organs
  ???
• Luxury genes hemoglobin, insulin

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Theory of Development
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1. Theory of Development

• ?? 2 ????? ??????????????? Expression ??? genes
  ??????? development ????????????????????????????
• gene ????? express ????????????????
• gene ???? express ??????????????????
• 1.1 Theory of Mosaic Development
• 1.2 Theory of Regulative Development

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1.1 Theory of Mosaic Development

• Differentiation ??? embryonic cells
  ????????????????? genetic potential
  ??????????????????????? ? ?????????????????????
• ??????? cell cycle ??????? development
  ???????????????? genetic material ??????? --gt
  ?????????????????
• ?????????????????????? organism
  ?????????????????????????????? (mosaic)
• Embryo ???????? Mosaic embryo

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• ??????? ???????????????? Genes ???????????????
• genes ?????????????? potential ???????
  differentiation ?? ????????
• 1. Housekeeping genes ???
• 2. Luxury genes
• ?? invertebrate ??????????????????????? embryo
  ??????????? 2 ????? ?????? ???
• ???????? programmed ?????? ???????????
  differentiate ?????? ?????????? ???? ??????????

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1.2 Theory of Regulative Development

• ????? embryo ??? eukaryote ???????????????????????
  ?????? 8 cells ???????????????????????
• ???? 8 ??????????? develop ???? 8 organisms
• ???????????????????????? 8 ????????? (regulated)
• ?????????????? Totipotent ??? ??????? genetic
  materials ?????????? ????????????????????? 8
  ??????????
• Embryo ???????? Regulative embryo

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• ??????? ????? embryo ????? genetic materials
  ????????????? ?????????????? 3 cell division
  cycles ??????????????????? mosaic development
• ?????????????? ???????? Regulative development
• ???? embryo ??? humans ????????????????????????
  ? (??? 8 ??)

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• ??????????????? totipotency ????????? ???
• ?? totipotent ???? stem cells/ precursor cells
  ??? ????????????????????????
• ??????? genetic potential ????????? ???? muscle
  cells ??? nerve cells
• ????? adult cell ????? 1 ????? ???? totipotent
  differentiated cells ????????????????????????????
  ?????????????????????? tissue culture

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• ??????? animals plants
• ????????? totipotent differentiated cells
  ????????????
• ????????????????? genetic material ??
  differentiation ???????? ???????????? ???
• ?????????????????????? genes ???????
• cell differentiation
• ??????????????????? cell differentiation
  ??????????? Epigenetic changes ???????????????????
  ?
• gene expression ???????????? genes ??????

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Substances in Development
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2. 1 Determinant

• ????????? differentiate ??? express specific
  function ?????????????????????? Determination
• Determination ???????????????????? point of no
  return ???? irreversible commitment ??
  Development program ???? fate ????????????????????
  ??
• ??????? ??? Effector substances ?? cytoplasm
  ????? ???? Determinants

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• Gradient of determinationsdeterminants ??????
  egg ??????????????????????????????????????????????
  ?? (gradient) ??? ?? --gt ???? (animal pole --gt
  vegetal pole) ?????? side --gt side

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• Determinants ??????? Maternal messages
• mRNA ????????????????????????????????????????????
  ??????????? egg (developing egg) ????
• Determinants ??????? Transcription factors
  ????????????? egg
• ???????????????? embryonic cells ??? embryo
  ??????????

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2.2 Inducers

• Substance ??????????????????????????????????????
• ??????????????????????????? ???? ???? Signal
  ??? cell ??? cell ????
• ?????????? embryo 3 ???? Mesoderm ?? induce
  development ??? Ectoderm
• ?????????? induce ??????????? ??????????

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2.3 Morphogens

• ???? subsets ??? determinant ??? inducer
• Morphogen ????????????? (morphology) ??? embryo
  ?????????????
• Morphogen ????????????????????????????????????????
  ? embryo ?????????? transplantation
• ???? ?? chick limb bud ?? Retinoic acid
  ????????????????????? ???????? (digits)

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• ????? Retinoic acid ???? morphogen
  ??????????????????????????????????????????????????
  ????
• Retinoic acid ????????????????????? hormones
  ?????? differentiation ???????

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II. Control of Gene Expressionin Differentiation
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II. Control of Gene Expression in Differentiation

• Differentiation ?????????? turn-on ??? genes
• ????????????
• ???? control ??? structural gene expression ?????
  
• Transcription,
• Posttranscription,
• Translation ???
• Posttranslation

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Control ?? Prokaryote

• ?????????????????????????? gene expression ???
  cellular activity
• ???? ?? bacteria ???????? Sporulation
• --gt Vegetative
• ??????????????? sigma (s) factor ??? RNA
  polymerase ??? ??????????????

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Control ?? Eukaryote

• Expression ??? luxury genes
• 1. Hormone activation of genes
• 2. Hormone-responsive elements
• 3. Light-induction of plant genes

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1. Hormone Activation on Genes

• Hormone ???????? turn on transcription ???
  specific genes ?? target cells ???
• 1. ?????? ??? ???????????? genes ?? nucleus
• 2. ??????? ??????? second messenger ??? cell
  membrane ?????? cytoplasm
• Hormone action ???? complex process ???? 2 ????
  ?????? receptor ????????? hormone

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Steroid Hormone

• Steroid hormone ?????????????? development ???
  differentiation
• Steroid hormone ??????? cell membrane ????
  cytoplasm ???? nucleus ???????? receptor ??
  nucleus
• Hormone-receptor complex ????? chromatin ??
  activate genes ?????????????????? Transcription

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• Effect ??? Steroid Hormone ??? Gene Expression

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Activation ??? Estrogen ??? Ovalbumin Gene ??
chick oviduct

• estrogen-receptor complex ?? binding site
  ?????????? 250-300 base pairs upstream ??? TATA
  box
• hormone-receptor complex ????? transcription
  factor ??? bind ??? stimulate ?????????? enhancer
  ??? gene

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Hormone ??????? family ????? receptor ?? nucleus

• ?????????????????? development
• 1) Glucocorticoid receptor mediate gene ???
• hormone cortisol
• 2) Vitamin D3 receptor
• 3) Thyroid hormone receptor
• 4) Retinoic acid receptor
• Response ???????? ???????????? receptor ???????

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2. Hormone-Responsive Elements (HRE)

• ??? Enhancer ???????????? receptor ??? hormone
  ??????? hormone-receptor complex
• Enhancer ?????????????????????? Promotor ??? gene
  ???????? RNA polymerase ?? transcription ?? gene
  ???
• ???? HRE ?????? hormone ??? receptor ????????

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2.1 HRE ?????? Retinoic Acid Receptor Retinoic
acid responsive element (RARE)

• ???? binding site ?? DNA
• ?????????
• Retinoic acid receptor (RAR)
• RAR ???????????????????
• ???????? Finger protein
• ?????? 2 Zinc fingers

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• Retinoic acid receptor (RAR) protein
• ?????? Retinoic acid responsive element (RARE)
• DNA sequence ??? RAR-RARE complex ?? DNA
• ???? Retinoic acid (R) ????????????? RAR-RARE
  complex
• RAR-RARE complex ????? stimulate gene
  ???????????
• RARE ???? growth hormone gene ?????? pituitary
  ???????? growth hormone

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Action ??? Retinoic Acid

• RAR (receptor) RARE (element)
• RAR-RARE Complex /----Promotor-----Gene-----/
• /-------RAR-RARE-Promotor-----Gene----
  -/ Transcription
• Retinoic Acid RNA Polymerase

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(No Transcript)
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2.2 HRE ?????? Thyroid hormone receptor (THR)

• RARE ???? enhancer ??? Thyroid hormone receptor
  (THR) ????
• ????? thyroid hormone ???????????? retinoic acid
  ????? ????????????? growth hormone
• ??? thyroid hormone receptor ?????? RAR ???
  dimer ????? growth hormone RARE --gt turn on
  growth hormone gene --gt growth hormone

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2.3 RARE ???? Enhancer ??? Vitamin D3 Receptor

• Vitamin D3 ???????????? Retinoic acid
• ????????? VDR ??? RAR ???????? ??? RARE
• ??????? turn on Osteocalcin gene --gt product
  ????????? differentiation ??? immature
  Osteoblasts
• Osteoblasts uptake calcium
• Osteoblasts differentiate ???? mature Osteocytes

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?????????? Cells ??????? response ???
hormone???????????? ????? ??

• hormone receptor ??????????? specificity ???????
• Hormones ????????? target ????? 2-3 cell types
• ???? Retinoic acid ?? vertebrate ?? receptor 3
  types
• ????? type RARa ???????????????????????
• Retinoic acid ??????? Morphogen ???????
• Hormone receptor ??????? protein ???????????
  differentiation ???????????

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3. Light-induction of plant genes

• ??????? (Seedling) ????????????????????
  ?????????? photosynthetic apparatus ???????
  chlorophyll ???????????????????
• ?????????????? seedling ????????????????????? ???
  enzyme ????? chlorophyll ???? light-activated
  enzyme ???? Ribose biphosphate carboxylase ????
  Rubisco

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Rubisco Gene

• ????????? Rubisco gene ??? light-inducible genes
• Promoter
• ??? -35 base pair region ?? TATA box
• Sequence ??? -35 ??? -46 ???? light dependent ???
• ?????????? -46 upstream ????????????????
• Enhancer
• Region ??? -327 ??? -48 ???? stimulate rubisco
  gene ??????????????????

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Promoter enhancer ??? Light response gene

• (a) Rubisco gene ??? pea cloned ??? petunia cells
• (b) Rubisco gene ??? pea cloned ??? tobacco

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Control Expression ??? gene ?? cell
differentiation ?? plants ??? animals

• Regulatory region / 5-flanking region ???
• cis-acting DNA ??? Control region
  ????????????????? structural gene ???? TATA box
  ??? GC box
• trans-acting protein ???? transcription factor
  ????? DNA ????????????? template

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III. Nature of Determination
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Determination

• ??? ????????????????????????????? ???????? cell
  ??????????? developmental pathway
• ????????????????????????????????????????
  Chromatin ??? factor ??????? histones ????????
  control regions ??? genes

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???? Determination

• 1. DNase Hypersensitivity
• 2. Control expression ??? 5S rRNA
• 3. DNA methylation

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1. DNase Hypersensitivity

• DNA ????????????? Nucleosomes (300 bp) ??
  chromatin ??????????? histones ??????? DNas
  ???????? DNase hypersensitive site

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• DNase hypersensitive region ????? 5- flanking
  region / regulatory region (promoter enhancer)
• ????????? turn on/off gene ????????? factor
  (protein) ??????????????????? hypersensitivity
  ?????????????? Nucleosome ????
• globin gene ??????????????
• Hypersensitivity region ??? 60-260
  upstream??????????????? nucleosome ????? embryo
  ???? 14 ???
• ?? Determination factor ??? globin gene active
  ????????? 14 ????????????

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2. Control ??? 5S rRNA gene expression

• 5S rRNA genes (??) ?? 20,000 genes ????????
• 2 family
• 1. Oocyte 5S rRNA genes 98 , transcription
  ????
• ????? ?? oocytes
• 2. Somatic 5S rRNA genes 2 , transcription
  ????
• ?? somatic cells

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Expression ??? rRNA genes 2 families

• ???? replication ??????????? cell division
  ??????????????????????????
• transcription factors RNA Pol III ?? factors ???
  TFIIIA, TFIIIB, ??? TFIIIC ???
• histones ?? hypersensitivity region
• ???? ?? immature egg ??? developing embryo ?????

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• ?? immuture egg
• Oocyte 5S rRNA genes express ???
• somatic 5S rRNA genes ??? repressed
• ?? developing embryo Embryo 3,200 cells
• TFIIIA ???????????????? ??????? 1 ??????? /
  oocyte rRNA gene
• ????? oocyte rRNA gene ??? repressed ??? histones
  ??? somatic rRNA gene ????? express

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3. DNA methylation

• Active genes ?????? low methyl groups ???? ?????
• Methylation ??? DNA
• ????? repress gene ????????????? ???
• ???? signal ??? DNA ????????? methylation ????
• ?? methylation ?? higher eukaryote ??????????? C
  ??????? 5-CG-3 dinucleotides

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Determination ??? mehtylation

• ????? 1) Repress gene activity ???
• 2) permanent
• ??????? Epigenetic mechanism ????? methylation
  ??????????????? genetic ???
• ????? gene turn off ??????????? development ????
  
• X chromosome ?? female ???????? methylated ???
  ???? develop ????
• Inactive X chromosome ??????????? Lyonized
• ???????????????????? Barr body

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Genes ??????? Determination

• ?? ???????? ?????????? mutation
• ?? genes ???????????? determination
  ????????????????????? ????????
• Homoeotic genes ???? Homeotic genes
• ?????????? mutation ?????????????????????????????
  (transformation) ?????????????????????????????????
  ???????

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• ???? Antennapedia (Antp) mutant
  ????????????????????
• ??????? genes ??? cells ?????????????
  ???????????????????????? ???? cells ??????????
  develop ?????????????? programmed ??? develop
  ??????
• Transformation ????????????? activity ???????
  genes
• ???????????? gene ????????????? mutated ????????
  transformation
• ??????? gene ??????? control genes ????? ???
  develop ???????? Homeotic gene

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• ??????? Homeotic gene ???? Master gene
  ???????????????? determination ???? (fate)
  ???????????????????????????????????
• ??? mutate gene ?????????? determination
  ???????????????? / program????
• Homeotic genes ?????????????? ?????????
  development
• ????????????????? Homeotic gene ???? 2 ????? ???
• Antennapedia complex (ANT-C) ???
• Bithorax complex (BX-C)

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Homeobox

• Common DNA sequence ?????? 180 bp ??
• ?? Homeotic genes ???? complex (cluster) genes
  ???
• ?? Non-homeotic genes ???????????????????
  transform ??? body part ??????????????????????????
  ?? homeotic genes ????? development
  ?????????????????????????? embryo

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????????? Homeobox

• 75 - 79 conserved
• share ??? control genes ??????? develop
  ????????????????
• code ??? protein ????? DNA-binding domain ???????
  positively charged ???
• protein ???????? transcription factor ?? migrate
  ???????? nucleus ????? control region ??? genes
  ????????????

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Arrangement ??? homeobox genes

• ????????????? vertebrate ??? invertebrate ???
• ???????? anterior-posterior body axis ??? express
  ???
• genes ?????????????????? cluster ???? genes ???
  express ????????? (anterior) ???
• genes ?????????????? cluster ??? express
  ????????????? (posterior)

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Maternal Effect Genes

• Genes ??? code ??? products ?? egg ???? ??????
  ??? products ???????????????????? ???? ????? egg
  ?? polarity
• products ?? effect ??? development ??? body parts
• bicoid (bcd) gene ??????? anterior body parts
  ???? heads thoraxes

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Segmentation genes

• Control organization ?????????????????? segments
• ftz gene ?? segment ???? segment ???? pair-rule
  genes ????????? embryo ???????
• engrailed gene ???? embryo ??????? anterior
  posterior

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Vertebrate homeoboxes

• sequence ??? homeoboxes ??? ??????????????
  vertebrate ?????????????? 95
• ?????????????? genes ???? cluster
  ?????????????????? express
• homeotic genes ???????????????? clusters express
• ?????????? ???
• homeotic genes ????????????????? clusters express
  ??????????

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• homeobox gene ??? vertebrate active ??????????
  active ??????????????? differentiation
• homeobox proteins ?? vertebrates ????????
  Transcription factor ??? Regulator ?? development
  ??? embryo
• ???? Pit -1 protein

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• Pit -1 protein ?? mouse dwarf (dw) gene
• ?????? development ??? pituitary glands ????????
  growth hormone, prolactin hormone ???
• thyroid - stimulating hormone
• ??????? Pit-1 ?? multiple effects ??? development
• ??? pituitary gland

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• Developmental pathway
• House keeping genes Luxury genes
• Mosaic development vs. Regulative development
• Totipotency vs. Epignetics
• Determinants, Inducers Mophogens
• Differentiation control in Prokaryote vs.
  Eukaryote
• Animal Hormone-induced genes Hormone
  responsive element
• Plant Light-induced genes
• DNA hypersensitivity, rRNA gene expression, and
  DNA methylation
• Homeotic genes Homeobox
• Maternal Effect genes
• Segmentation genes