1. Molecular Biology of the Cell
Alberts • Johnson • Lewis • Raff • Roberts • Walter
Molecular Biology of the Cell
Fifth Edition
Chapter 22
Development of Multicellular Organisms
Copyright © Garland Science 2008

2. 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

3. 4 essential processes involved in development
of multicellular organisms
Morphogens for inducing signaling events
Cell-cell interaction for fate/polarity determination
Figure Molecular Biology of the Cell (© Garland Science 2008)

4. 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)

5. (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)

6. Basic anatomical features are shared in most animals.
Egg cell divides to form an epithelial sheet
Gastrulation
Ectoderm
Endoderm
Mesoderm between the two layers
Initial intucking of the epithelium during sea urchin gastrulation.
Figure 22-3 (part 1 of 3) Molecular Biology of the Cell (© Garland Science 2008)

7. Similar basis body plans, radically different body structures
Regulatory DNA defines gene expression and development program.
Same set of genes
Different states
Different arrangements
of regulatory modules
Figure Molecular Biology of the Cell (© Garland Science 2008)

8. 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 Molecular Biology of the Cell (© Garland Science 2008)

9. Cell-cell interaction studies in large animal embryos (birds/amphibians)
Some striking results obtained by experimental embryology.
Split of an early amphibian embryo into two parts with a hair loop.
An amphibian embryo at a somewhat later stage. Grafting of a group of cells from another embryo at that stage.
Figure Molecular Biology of the Cell (© Garland Science 2008)

10. A standard test for cell fate determination
Developmental decision-making
can occur long before visible differentiation
committed/specified/determined
A standard test for cell fate determination
Figure Molecular Biology of the Cell (© Garland Science 2008)

11. 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 Molecular Biology of the Cell (© Garland Science 2008)

12. Tbx4 and Pitx1: Expressed in the leg bud.
Misexpression of Pitx1in the wing bud causes the limb to develop with leg-like characteristics.
Figure Molecular Biology of the Cell (© Garland Science 2008)

13. Inductive signals to create different cell fates.
Equivalence group → distinct cell fate
Interaction by cell-cell contacts or diffusible molecules.
Figure Molecular Biology of the Cell (© Garland Science 2008)

14. Distinct sister cell fates by asymmetric division
: Intrinsic mechanism independent of extracellular signal
Asymmetric segregation of cell fate determinant(s)
Figure Molecular Biology of the Cell (© Garland Science 2008)

15. Cell-cell interaction: Genesis of asymmetry through positive feedback.
X inhibits X synthesis in adjacent cells
Lateral inhibition
Figure Molecular Biology of the Cell (© Garland Science 2008)

16. Memory of the stable states
Positive feedback
Symmetry breaking
Bistability
Memory of the stable states
Similar principles in cell fate decisions, regionalization
of tissues, asymmetry within a cell, etc

17. 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 Molecular Biology of the Cell (© Garland Science 2008)

18. morphogen in chick limb development.
Sonic hedgehog as a
morphogen in chick limb development.
Figure Molecular Biology of the Cell (© Garland Science 2008)

20. 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 Molecular Biology of the Cell (© Garland Science 2008)

21. Patterning by sequential induction.
A series of inductive interactions can generate many types of cells, starting from only a few.
Figure Molecular Biology of the Cell (© Garland Science 2008)

22. Morphogen gradient formation
Simple diffusion
Receptor-mediated trap/endocytosis
Excellular matrix-mediated reduction
Cytoneme-mediated transport

23. An excellent model organism for genetic analysis
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

24. Figure 22-17 Molecular Biology of the Cell (© Garland Science 2008)

25. Figure 22-18 Molecular Biology of the Cell (© Garland Science 2008)

26. 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 Molecular Biology of the Cell (© Garland Science 2008)

27. 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.

28. To identify maternal effect lethal mutations causing defective early cleavage patterns,
Mutant embryos with no catastrophic defects in mitosis or cytokinesis and that
Arrest at late stages of cellular proliferation
3. partition-defective: par-1, par-2, par-3, par-4

29. Abnormal distribution of P granule in par mutants

30. Asymmetric partitioning in worm embryos and vertebrate epithelia
Anterior
PAR3, PAR6, PKC3
PAR1, PAR2

32. The pattern of cell divisions in early C. elegans embryo.
Asymmetric P-granule distribution by Par (partition- defective) 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 Molecular Biology of the Cell (© Garland Science 2008)

33. 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.

34. 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 Molecular Biology of the Cell (© Garland Science 2008)

35. Stage-specific pattern of cell divisions

36. 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 Molecular Biology of the Cell (© Garland Science 2008)

37. Lin4 antagonizes lin-14 post-transcriptionally.

38. 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

39. Apoptotic cell death in C. elegans.
Ced9
1030 somatic cells
131 cells undergo PCD
Ced3/Ced4
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 Molecular Biology of the Cell (© Garland Science 2008)

43. Development of multicellular organisms
Part II. Drosophila melanogaster

44. Drosophila and the molecular genetics of pattern formation: genesis of the body plan
Figure Molecular Biology of the Cell (© Garland Science 2008)

45. Figure 22-25 Molecular Biology of the Cell (© Garland Science 2008)

46. Segmentation of embryo
Syncytial blastoderm
Gastrulation,
Segmentation,
Head involution
Figure Molecular Biology of the Cell (© Garland Science 2008)

47. Relationship between embryo and larval segments
Figure Molecular Biology of the Cell (© Garland Science 2008)

48. Syncytium to cellularized blastoderm
Surface view of cellular blastoderm
: actin-chromosome stain
Figure 22-28a Molecular Biology of the Cell (© Garland Science 2008)

49. 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 Molecular Biology of the Cell (© Garland Science 2008)

50. Genetic control of anterior-posterior patterning
The domains of the
anterior (bicoid),
posterior (nanos),
and
terminal (torso)
systems
of egg-polarity genes
Figure Molecular Biology of the Cell (© Garland Science 2008)

51. AP and DV patterning in the ovary
Follicle cells provide AP and ventral signals.
Figure Molecular Biology of the Cell (© Garland Science 2008)

52. 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 Molecular Biology of the Cell (© Garland Science 2008)

53. Nuclear localization of Dorsal and DV gradient
IkB
NFkB
Nuclear localization of Dorsal and DV gradient

55. 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 Molecular Biology of the Cell (© Garland Science 2008)

56. from cells expressing Twist.
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 Molecular Biology of the Cell (© Garland Science 2008)

57. The vertebrate body plan
A dorsoventral inversion of the insect body plan.
Dorsal Dpp Chordin
Ventral Sog BMP4
Drosophila
Vertebrates
Figure Molecular Biology of the Cell (© Garland Science 2008)

58. 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 Molecular Biology of the Cell (© Garland Science 2008)

59. The regulatory hierarchy of egg-polarity
Gap, Pair-rule, and Homeotic selector genes
Figure Molecular Biology of the Cell (© Garland Science 2008)

60. of the regulatory DNA of the Eve gene
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 Molecular Biology of the Cell (© Garland Science 2008)

61. 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 Molecular Biology of the Cell (© Garland Science 2008)

62. Engrailed, a segment-polarity gene
Engrailed, a segment-polarity gene. The Engrailed pattern, once established, is preserved throughout the animal’s life.
Figure Molecular Biology of the Cell (© Garland Science 2008)

63. Expression pattern compared to the chromosomal locations of the genes of the Hox complex.
Figure Molecular Biology of the Cell (© Garland Science 2008)

64. Homeotic transformation
Antennapedia
Bithorax (haltere to wing)

65. 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.

66. The Hox complexes of an insect and a mammal compared and related to body regions
Figure Molecular Biology of the Cell (© Garland Science 2008)

67. the patterning of appendages
Organogenesis &
the patterning of appendages

68. Creation of mutant cells by induced somatic recombination
Figure Molecular Biology of the Cell (© Garland Science 2008)

69. Ectopic overexpression of transgenes by UAS-GAL4 systme
Figure 22-50b Molecular Biology of the Cell (© Garland Science 2008)

70. (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)

72. Figure 22-51 Molecular Biology of the Cell (© Garland Science 2008)

73. Gene expression domains in the wing imaginal disc,
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 Molecular Biology of the Cell (© Garland Science 2008)

74. Compartments in the adult wing.
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.
En expression in the posterior compartment
(B)
Figure 22-54a Molecular Biology of the Cell (© Garland Science 2008)

75. Four Familiar Signaling Pathways Combine to Pattern the Wing Disc: Wingless, Hedgehog, Dpp, and Notch
Figure Molecular Biology of the Cell (© Garland Science 2008)

76. 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 Molecular Biology of the Cell (© Garland Science 2008)

77. Figure 22-58 Molecular Biology of the Cell (© Garland Science 2008)

78. Sensory mother cells in the wing imaginal disc.
Figure Molecular Biology of the Cell (© Garland Science 2008)

79. Cell-cell interaction: Genesis of asymmetry through positive feedback.
X inhibits X synthesis in adjacent cells
Lateral inhibition
Figure Molecular Biology of the Cell (© Garland Science 2008)

80. Lateral Inhibition Singles Out Sensory Mother Cells Within Proneural Clusters
SOP
Figure 22-60a Molecular Biology of the Cell (© Garland Science 2008)

81. Selection of SOP by lateral inhibition
Reduced lateral inhibition
- More sensory organs
Figure 22-60b Molecular Biology of the Cell (© Garland Science 2008)

82. Basic helix-loop-helix family proteins in neurogenesis
Atonal: R8, chordotonal internal sensory
Amos: md neuron, olfactory sensilla
Math1: proprioceptive sensory (hearing)
Math5: RGCs in visual system
Atonal family
Achaete: external sensory organ
Scute: redundant with Ac
Mash1
Mash2
Achaete-Scute
family
NeuroD
NeuroD2
Math2
Math3
NeuroD family

83. Genetic control of neural development:
Proneural (Ac-Sc) & neurogenic genes (Notch-Delta)

84. 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