Presentation is loading. Please wait.

Presentation is loading. Please wait.

Chapter 21. Development of Multicellular Organisms Sydney Brenner, 1960.

Similar presentations

Presentation on theme: "Chapter 21. Development of Multicellular Organisms Sydney Brenner, 1960."— Presentation transcript:

1 Chapter 21. Development of Multicellular Organisms Sydney Brenner, 1960

2 Mutation vs. variation VariationMutation

3 Types of mutation 1. No phenotype -Amorph 2. Loss of function -Null -Hypomorph 3. Gain of function -Hypermorph -Antimorph (dominant negative)

4 1. Robust model for the behavior of individual and identified cells  1000 somatic germ cells 2. Convenient model for genetics  Single heterozygote worm can produce homozygous progeny 3. Cell fates and lineages are almost perfectly predictable

5 Mechanisms for C. elegans development Polarity formation by maternal effectors Cell-cell interactions to make complex patterns Heterochronic genes Apoptosis

6 1. Maternal effect genes mRNA from mother is asymmetrically distributed along anteroposterior axis Par (partitioning defective) genes bring P granules to posterior pole One cell having P granule give rise to germ cells

7 2. Cell-cell interactions to make complex patterns

8 P 2 -EMS interaction: 1. Mom mutants without gut -Mom gene (Wnt) expressed in P 2 cell -Frizzled gene (Wnt receptor) expressed in EMS cells 2. Pop mutants with extraguts -Pop genes encode LEF-1/TCF homolog -Reduced pop activity  gut -Increased Pop activity  muscle 2. Cell-cell interactions to make complex patterns

9 Cells change over time in their responsiveness to signals At four cells Anterior cell specification  depend on Notch signals At 12-cell stage, both Aba and Abp progenitors exposed to Notch signals  Granddaughter of Aba cells induce pharynx  Granddaughter of Abp cells unresponsive to Notch

10 Heterochronic genes control the timing of development Heterochronic phenotypes: The cells in a larva of one stage behave as though they belong to a larva of a different stages, or cells in the adult carry on dividing as though they belonged to a larva lin-4 for the transition larval stage1  3 let-7 for the transition late larva  adult


12 Apoptosis Cell death abnormal gene -ced-3, ced-4, egl-1 (caspase, Apaf-1, BAD homolog)  cause cell death -ced-9 (Bcl-2 homolog)  repress cell death

13 The Nobel Prize in Physiology or Medicine 2002 "for their discoveries concerning 'genetic regulation of organ development and programmed cell death'" Sydney BrennerH. Robert HorvitzJohn E. Sulston 1/3 of the prize United KingdomUSAUnited Kingdom The Molecular Sciences Institute Berkeley, CA, USA Massachusetts Institute of Technology (MIT) Cambridge, MA, USA The Wellcome Trust Sanger Institute Cambridge, United Kingdom b (in Union of South Africa) b. 1947b. 1942

14 Drosophila and the molecular genetics of pattern formation: Genesis of the body plan Seymor Benzer


16 Overall procedures


18 Syncytial Specification Pole cells

19 Maternal effects Cytoplasmic bridges Egg polarity determination A-P and D-V axis

20 Egg polarity genes (Maternal effectors)


22 Dorsoventral axis Dorsal protein (NF-kB): -D orsally, the protein is present in the cytoplasm and absent from the nuclei; ventrally, it is depleted in the cytoplasm and concentrated in the nuclei. -Toll gene controls the redistribution

23 Dorsoventral specification Dorsal protein concentration High  activate twist, repress dpp (decapentaplegic) Intermediate  sog (short gastrulation)

24 Dorsolventral specification Fate map

25 Distribution of twist in mesodermal cells

26 Anteroposterior specification Maternal genes, bicoid, nanos Segment genes refine the pattern –Zygotic genes –Six gap genes: Coarse subdivision –Pair rule genes: Segment alteration –Segment-polarity genes: Homeotic selector genes

27 Anteroposterior specification Krupel lacks 8 segments (T1-A5) Even-skipped (eve) lacks odd- numbered parasegments Fushi tarazu (ftz) lacks even-numbered parasegments Gooseberry posterior half is the mirror image of anterior half

28 Formation of parasegments Expression pattern of ftz (brown) and eve (gray) Pair rule genes

29 Segment polarity genes Forms parasegments polarity Involves cell-cell interactions Associated with two signaling pathways –Wnt –Hedgehog

30 Regulatory hierarchy

31 The Nobel Prize in Physiology or Medicine 1995 "for their discoveries concerning the genetic control of early embryonic development" Edward B. LewisChristiane N ü sslein-Volhard Eric F. Wieschaus 1/3 of the prize USAFederal Republic of Germany USA California Institute of Technology Pasadena, CA, USA Max-Planck-Institut f ü r Entwicklungsbiologi e T ü bingen, Federal Republic of Germany Princeton University Princeton, NJ, USA b d b. 1942b. 1947

32 Homeotic mutations

33 Homeotic selector genes Hox gene complex –Antennapedia complex –Bithorax complex Contain homeodomain –60 amino acids –DNA binding region Regulate positional information

34 Hox gene complex

35 Expression of hox gene complex

36 Hox gene complex

37 Comparison of hox gene expression


39 Organogenesis and patterning of appendage

40 Methods in fly genetics: Somatic mutations Mosaic

41 Methods in fly genetics: Enhancer trap

42 Imaginal discs Groups of cells set aside undifferentiated 19 discs (9 pairs + 1 genital) Develop into organs such as leg, wing, eyes etc.

43 Specific ID genes define organs Distal-less  expressed in appendages Pax-6  expression in eyes

44 Wing formation Sector formation in wing disc Four compartments foms engrailed, apterous genes are involved

45 Wing formation

46 (A) The shapes of marked clones in the Drosophila wing reveal the existence of a compartment boundary. The border of each marked clone is straight where it abuts the boundary. Even when a marked clone has been genetically altered so that it grows more rapidly than the rest of the wing and is therefore very large, it respects the boundary in the same way (drawing on right). Note that the compartment boundary does not coincide with the central wing vein. (B) The pattern of expression of the engrailed gene in the wing, revealed by the same technique as for the adult fly shown in Figure 21–40. The compartment boundary coincides with the boundary of engrailed gene expression.

47 Limb formation

48 Bristle formation achaete, scute genes -HLH -Proneural genes Scute expression in wing disc

49 Lateral inhibition Notch-delta

50 Lateral inhibition Notch somatic mutation Loss of lateral inhibition Bristle patches

51 Bristle formation Numb gene -Block Notch gene activity

52 Bristle formation Planar polarity genes Orienting bristle backward position frizzled proteins  control planar polarity dishevelled  downstream of frizzled

53 Bristle formation

Download ppt "Chapter 21. Development of Multicellular Organisms Sydney Brenner, 1960."

Similar presentations

Ads by Google