Alberts • Johnson • Lewis • Raff • Roberts • Walter
Molecular Biology of the Cell
Fifth Edition
Chapter 22
Development of Multicellular
Organisms
Copyright © Garland Science 2008
Development of multicellular organisms
 Introduction: general features of animal
development
 Caenorhabditis elegans:
Cell-cell interaction in embryogenesis
 Drosophila melanogaster:
Pattern formation: Genesis of the body plan
4 essential processes involved in development
of multicellular organisms
• Morphogens for inducing signaling events
• Cell-cell interaction for fate/polarity determination
Functional conservation of developmental genes
Homologous proteins functioning interchangeably in the development of mice
and flies.
 Drosophila Engrailed protein can be substituted for the corresponding gene for the
Engrailed-1protein of the mouse.
 Loss of Engrailed-1 in the mouse causes a defect in its brain (the cerebellum fails
to develop); the Drosophila protein rescues this deformity.
Figure 22-2a Molecular Biology of the Cell (© Garland Science 2008)
(Top) Ectopic expression of fly Eyeless in the leg
(Bottom) Ectopic expression of squid Eyeless
Figure 22-2b Molecular Biology of the Cell (© Garland Science 2008)
Basic anatomical features
are shared in most animals.
 Egg cell divides to form an
epithelial sheet
 Gastrulation
• Ectoderm
• Endoderm
• Mesoderm between the two
layers
Figure 22-3 (part 1 of 3) Molecular Biology of the Cell (© Garland Science 2008)
Initial intucking
of the epithelium
during sea urchin
gastrulation.
Similar basis body plans, radically different body structures
Regulatory DNA defines gene expression and development program.
Same set of genes
Different arrangements
of regulatory modules
Different states
Figure 22-4 Molecular Biology of the Cell (© Garland Science 2008)
Analysis of development
 Description of morphological changes
Experimental embryology in 19th century
 Causal mechanisms
 Experimental embryologists’ approach
Transplantation & track cell (tissue)-cell interaction
through division, transformation, migration
 Complementary approaches
Developmental geneticists
Figure 22-5 Molecular Biology of the Cell (© Garland Science 2008)
Cell-cell interaction studies in large animal embryos (birds/amphibians)
Some striking results obtained by experimental embryology.
(A)Split of an early amphibian embryo into two parts with a hair loop.
(B)An amphibian embryo at a somewhat later stage. Grafting of a group of cells from another
embryo at that stage.
Figure 22-6 Molecular Biology of the Cell (© Garland Science 2008)
Developmental decision-making
 can occur long before visible differentiation
 committed/specified/determined
A standard test for cell fate determination
Figure 22-7 Molecular Biology of the Cell (© Garland Science 2008)
Positional values (information)
: Position-specific character of cells
The early leg-bud cells are already
determined as leg, but
are not yet irrevocably committed
to form a particular part of the leg.
Ectopic expression
: Eyeless case
Figure 22-8 Molecular Biology of the Cell (© Garland Science 2008)
 Tbx4 and Pitx1: Expressed in the leg bud.
 Misexpression of Pitx1in the wing bud causes the limb to develop with
leg-like characteristics.
Figure 22-9 Molecular Biology of the Cell (© Garland Science 2008)
Inductive signals to create different cell fates.
Equivalence group → distinct cell fate
Interaction by cell-cell contacts or diffusible molecules.
Figure 22-10 Molecular Biology of the Cell (© Garland Science 2008)
Distinct sister cell fates by asymmetric division
: Intrinsic mechanism independent of extracellular signal
Asymmetric segregation of cell fate determinant(s)
Figure 22-11 Molecular Biology of the Cell (© Garland Science 2008)
Cell-cell interaction:
Genesis of asymmetry through positive feedback.
X inhibits X synthesis in
adjacent cells
Lateral inhibition
Figure 22-12 Molecular Biology of the Cell (© Garland Science 2008)
Positive feedback
Symmetry breaking
Bistability
Memory of the stable states
Similar principles in cell fate decisions, regionalization
of tissues, asymmetry within a cell, etc
Limited number of signaling pathways
: coordinate spatial patterning of embryos
: Used repeatedly during development
Some inducers are long-range morphogens that function in gradients.
Table 22-1 Molecular Biology of the Cell (© Garland Science 2008)
Sonic hedgehog as a
morphogen in chick limb
development.
Figure 22-13 Molecular Biology of the Cell (© Garland Science 2008)
Two ways to create a morphogen
gradient.
(A) By localized production of a
morphogen that diffuses away from its
source.
(B) By localized production of an inhibitor that diffuses away from its source and
blocks the action of a uniformly distributed inducer.
Figure 22-14 Molecular Biology of the Cell (© Garland Science 2008)
Patterning by sequential induction.
A series of inductive interactions can generate many types of cells, starting
from only a few.
Figure 22-16 Molecular Biology of the Cell (© Garland Science 2008)
Morphogen gradient formation
 Simple diffusion
 Receptor-mediated trap/endocytosis
 Excellular matrix-mediated reduction
 Cytoneme-mediated transport
S. Brenner




R. Horvitz
J. Sulston
An excellent model organism for genetic analysis
Small number of cells with fixed cell lineage
Self-fertilization in hermaphrodite (female with sperms)
Genome sequenced, anatomy reconstructed by EM
Figure 22-17 Molecular Biology of the Cell (© Garland Science 2008)
Figure 22-18 Molecular Biology of the Cell (© Garland Science 2008)
Maternal effect genes regulate asymmetric cell division
Asymmetric divisions
: segregating P granules into the germline founder cell.
DNA dye
P granule antibody
Sperm entry site: future posterior pole
Figure 22-19 Molecular Biology of the Cell (© Garland Science 2008)
Isolation of Maternal Effect Lethal Mutations
• Egg laying defective animals were mutagenized,
and their progeny were cloned onto single cultures.
• F1 animals with a maternal effect lethal mutation
(m/+) produce viable eggs (+/+, m/+, and m/m)
that hatch within and consume the parent.
• m/m F2 animals produce only inviable eggs and
are therefore not consumed.
To identify maternal effect lethal mutations
causing defective early cleavage patterns,
1. Mutant embryos with no catastrophic
defects in mitosis or cytokinesis and that
2. Arrest at late stages of cellular
proliferation
3. partition-defective: par-1, par-2, par-3, par-4
Abnormal distribution of P granule in par mutants
Asymmetric partitioning in worm embryos and vertebrate epithelia
Anterior
PAR3, PAR6, PKC3
PAR1, PAR2
30
31
The pattern of cell divisions in
early C. elegans embryo.
 Asymmetric P-granule
distribution by Par (partitiondefective) proteins.
 At the 16-cell stage, there is just
one cell that contains the P
granules.
 This one cell gives rise to the
germ line.
Figure 22-20 Molecular Biology of the Cell (© Garland Science 2008)
Molecular mechanism of cell fate decision
 Manipulation of embryo with laser (ablation or position change)
 Genetic screen for specific mutants
 Mom (more mesoderm) mutations: fails to generate EMS cells. No
gut: One gene is wnt, the other is Fz.
 Pop (posterior pharynx defective): extra gut cells.
 One gene is tcf (downregulated by Wnt). Pop1 mutants have more
Wnt signaling: Both daughters of EMS becomes gut cells.
• Mom (Wnt & Fz): more mesoderm in mom• Pop1 (more Wnt signaling, more gut cells in pop1-)
Cell signaling pathways in a four-cell embryo.
 P2 cell sends an inductive signal (Notch) to Abp (ABa cell respond to the
same signal, but it is out of contact with P2.
 Meanwhile, a Wnt signal from P2 cell causes the EMS cell to orient its
mitotic spindle and generate MS and E cell (gut founder) due to different
exposure to Wnt.
Figure 22-21 Molecular Biology of the Cell (© Garland Science 2008)
Stage-specific pattern of cell divisions
Heterochronic Genes Control the Timing of Development
Green: Lin14+
Premature occurrence of the
pattern of cell division and
differentiation characteristic
of a late larva
reiterate the first larval stage
patterns
Figure 22-22 Molecular Biology of the Cell (© Garland Science 2008)
Lin4 antagonizes lin-14 post-transcriptionally.
Lin-14
Lin-4
Hormonal control of developmental timing
• Metamorphosis in insects and amphibians
• Puberty in mammals (McCune Albright syndrome)
 GOF of lutenizing hormone receptor (LCGR)
in precaucious puberty (higher cAMP & testosterone)
 LOF: delayed puberty
Ced9
Ced3/Ced4
1030 somatic cells
131 cells undergo PCD
Apoptotic cell death in C.
elegans.
Death depends on Ced3 and
Ced4 genes in the absence of
Ced9 expression—all in the
dying cell itself.
The subsequent engulfment and
disposal of the remains depend
on other genes in the neighboring
cells.
Figure 22-23 Molecular Biology of the Cell (© Garland Science 2008)
Development of multicellular organisms
Part II. Drosophila melanogaster
Drosophila and the molecular genetics
of pattern formation: genesis of the
body plan
Figure 22-24 Molecular Biology of the Cell (© Garland Science 2008)
Figure 22-25 Molecular Biology of the Cell (© Garland Science 2008)
Segmentation of embryo
Syncytial blastoderm
Gastrulation,
Segmentation,
Head involution
Figure 22-26 Molecular Biology of the Cell (© Garland Science 2008)
Relationship between embryo and larval segments
Figure 22-27 Molecular Biology of the Cell (© Garland Science 2008)
Syncytium to cellularized blastoderm
Surface view of cellular blastoderm
: actin-chromosome stain
Figure 22-28a Molecular Biology of the Cell (© Garland Science 2008)
Fate map of an embryo at the cellular blastoderm stage.
During gastrulation,
the cells along the ventral midline invaginate to form mesoderm.
the cells fated to form the gut invaginate near each end of the embryo.
Figure 22-29 Molecular Biology of the Cell (© Garland Science 2008)
Genetic control of anterior-posterior patterning
The domains of the
anterior (bicoid),
posterior (nanos),
and
terminal (torso)
systems
of egg-polarity genes
Figure 22-30 Molecular Biology of the Cell (© Garland Science 2008)
AP and DV patterning in the ovary
Follicle cells provide AP and
ventral signals.
Figure 22-31 Molecular Biology of the Cell (© Garland Science 2008)
Four egg-polarity gradient systems
The receptors Toll and Torso are distributed all over the membrane; the
coloring indicates where they become activated by extracellular ligands.
Bicoid protein gradient
Figure 22-32 Molecular Biology of the Cell (© Garland Science 2008)
IkB
NFkB
Nuclear localization of Dorsal and DV gradient
Morphogen gradients patterning DV axis of embryo
The concentration gradient of
Dorsal protein.
Dorsally, it is cytoplasmic.
Ventrally, it becomes nuclear via
Toll signaling.
High Dpp activity: most dorsal tissue
Intermediate: dorsal ectoderm
Low: neuogenic ectoderm
Figure 22-34 Molecular Biology of the Cell (© Garland Science 2008)
Origin of the mesoderm
from cells expressing Twist.
Twist (bHLH)-expressing cells move into the interior
of the embryo to form mesoderm. The nerve system
moves to the ventral region.
Dorsal: Dpp is induced
Ventral: Sog (short gastrulation), Chordin homolog, Dpp antagonist
Figure 22-35 Molecular Biology of the Cell (© Garland Science 2008)
The vertebrate body plan
A dorsoventral inversion of the insect body plan.
Dorsal
Ventral
Drosophila
Dpp
Sog
Figure 22-36 Molecular Biology of the Cell (© Garland Science 2008)
Vertebrates
Chordin
BMP4
Anterior-posterior patterning
Three classes of segmentation genes
The shaded area in green on the normal larva (left) are deleted in the
mutant or are replaced by mirror-image duplicates of the unaffected regions.
Figure 22-37 Molecular Biology of the Cell (© Garland Science 2008)
The regulatory hierarchy of
egg-polarity
Gap, Pair-rule, and Homeotic
selector genes
Figure 22-38 Molecular Biology of the Cell (© Garland Science 2008)
Modular organization
of the regulatory DNA of the Eve gene
Analysis of various eve-lacZ reporter expression
: lacZ mRNA in situ-anti-Eve double stain
Figure 22-39 Molecular Biology of the Cell (© Garland Science 2008)
The formation of Ftz and Eve stripes.
Ftz (brown) and Eve (gray) are both pairrule genes. Their
expression patterns are at first blurred but rapidly resolve into
sharply defined stripes.
Figure 22-40 Molecular Biology of the Cell (© Garland Science 2008)
Engrailed, a segment-polarity gene. The Engrailed pattern,
once established, is preserved throughout the animal’s life.
Figure 22-41 Molecular Biology of the Cell (© Garland Science 2008)
Expression pattern compared to the chromosomal
locations of the genes of the Hox complex.
Figure 22-44 Molecular Biology of the Cell (© Garland Science 2008)
Homeotic transformation
Antennapedia
Bithorax (haltere to wing)
Ubx: T3 discs (haltere and 3rd leg) > T2 discs (wing and 2nd leg)
- Loss of Ubx in T3: transformation of T3 to T2
(haltere to wing, 3rd leg to 2nd leg)
Antp : selector for leg identity, repression of antennal fate
- Ectopic Antp in the antenna: transform antennae to legs.
The Hox complexes of an
insect and a mammal
compared and related to
body regions
Figure 22-46 Molecular Biology of the Cell (© Garland Science 2008)
Organogenesis &
the patterning of appendages
Creation of mutant cells
by induced somatic recombination
Figure 22-49 Molecular Biology of the Cell (© Garland Science 2008)
Ectopic overexpression of transgenes by
UAS-GAL4 systme
Figure 22-50b Molecular Biology of the Cell (© Garland Science 2008)
(Top) Ectopic expression of fly Eyeless in the leg
(Bottom) Ectopic expression of squid Eyeless
Figure 22-2b Molecular Biology of the Cell (© Garland Science 2008)
Figure 22-51 Molecular Biology of the Cell (© Garland Science 2008)
Wing pouch
Gene expression
domains in the wing
imaginal disc,
defining quadrants of
the future wing.
The wing blade itself
derives from the wing
pouch. It is divided into
four quadrants by the
expression of Apterous
and Engrailed
Figure 22-53 Molecular Biology of the Cell (© Garland Science 2008)
(A)
Compartments in the adult wing.
(A) The shapes of marked clones reveal
the existence of a compartment
boundary. The border of each
marked clone is straight where it
abuts the boundary.
(B) En expression in the posterior
compartment
Figure 22-54a Molecular Biology of the Cell (© Garland Science 2008)
(B)
Four Familiar Signaling Pathways Combine to Pattern the
Wing Disc: Wingless, Hedgehog, Dpp, and Notch
Figure 22-55 Molecular Biology of the Cell (© Garland Science 2008)
Similar Mechanisms Pattern the Limbs of Vertebrates
(A) A wing bud of a chick embryo. At the distal margin of the
limb bud a thickened ridge can just be seen—the apical
ectodermal ridge.
(B) Expression patterns of key signaling proteins and gene
regulatory factors in the chick limb bud.
Figure 22-57 Molecular Biology of the Cell (© Garland Science 2008)
Figure 22-58 Molecular Biology of the Cell (© Garland Science 2008)
Sensory mother cells in
the wing imaginal disc.
Figure 22-59 Molecular Biology of the Cell (© Garland Science 2008)
Cell-cell interaction:
Genesis of asymmetry through positive feedback.
X inhibits X synthesis in
adjacent cells
Lateral inhibition
Figure 22-12 Molecular Biology of the Cell (© Garland Science 2008)
Lateral Inhibition Singles Out Sensory Mother Cells
Within Proneural Clusters
SOP
Figure 22-60a Molecular Biology of the Cell (© Garland Science 2008)
Selection of SOP by lateral inhibition
Reduced lateral inhibition
- More sensory organs
Figure 22-60b Molecular Biology of the Cell (© Garland Science 2008)
Basic helix-loop-helix family proteins in neurogenesis
Atonal: R8, chordotonal internal sensory
Atonal family Amos: md neuron, olfactory sensilla
Math1: proprioceptive sensory (hearing)
Math5: RGCs in visual system
Achaete: external sensory organ
Achaete-ScuteScute: redundant with Ac
family
Mash1
Mash2
NeuroD
NeuroD family NeuroD2
Math2
Math3
82
Genetic control of neural development:
Proneural (Ac-Sc) & neurogenic genes (Notch-Delta)
83
Use of genetic model systems
•Identify developmental genes
•Functional analysis in vivo
•Reveal functional conservation
•New insights for studying higher animals
Axial patterning, induction, fate determination,
cell death , signaling pathways and more