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Drosophila melanogaster development

Drosophila melanogaster development. How do Drosophila embryos develop? How can one use genetics to find genes that regulate embryo development?. Life cycle of Drosophila . egg. 4 days. female. embryogenesis. pupa. DROSOPHILA LIFE CYCLE. 1 day. larva. 1st instar. 1 day. 4 days.

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Drosophila melanogaster development

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  1. Drosophila melanogaster development How do Drosophila embryos develop? How can one use genetics to find genes that regulate embryo development?

  2. Life cycle of Drosophila egg 4 days female embryogenesis pupa DROSOPHILALIFE CYCLE 1 day larva 1st instar 1 day 4 days larva 2 days 2nd instar larva 3rd instar

  3. OOGENESIS IN DROSOPHILA Germarium Germline Cyst Formation Cystoblast germline stem cells follicle stem cells ring canal Pro-Oocyte (undergoes meiosis) germline: stem cell > cystoblast > 1 oocyte + 15 nurse cells

  4. OOGENESIS IN DROSOPHILA Germarium Vitellarium follicle cells nurse cell oocyte oocyte germline stem cells stalk follicle stem cells border cells oocyte + nurse cells surrounded by (somatic) follicle cells

  5. Drosophila oocyte and supporting cells Nurse cells Ring canals Oocyte Follicle cells (from Gonzalez-Reyes and St Johnston (1994) Science 266: 639-642.)

  6. Drosophila oocyte and supporting cells Nurse cell nuclei Follicle cell nuclei (from Gonzalez-Reyes and St Johnston (1994) Science 266: 639-642.)

  7. Nuclear divisions start without cell division in Drosophila (superficial cleavage) Fig. 9.1 Zygotic gene expression begins

  8. T1 T2 acron T3 head A1 A2 thorax A3 abdomen A4 A5 telson A6 A7 A8 Larvae already have substantial patterning anterior T ventral dorsal A posterior “stripy” expression epithelium of segmentation gene (6,000 cells) fushi tarazu (ftz) egg blastoderm fate map larva (cuticle)

  9. The fruit fly body plan is assembled in 24 hours: How?

  10. Christiane Nüsslein-Volhard and Eric Wieschaus used genetics to identify proteins that set up the embryonic body plan

  11. wildtype Wieschaus and Nüsslein-Volhard looked for mutants that affect the fly body plan

  12. Genes identified in a famous screen for Drosophila mutants with embryo patterning defects

  13. Screen for developmental mutants (Drosophila) Lethal hits = 100% (essential genes - ca. 5.000) (efficiency of mutagenesis = number of hits per gene) zygotic mutants 100 % embryonal-lethal mutants 25 % with morphological defects 3 % - segmentation defects (AP) 0.5 % - tissue types defective (DV) 0.5 % female-sterile mutants 8 % with effects on embryogenesis 2 % (= maternal-effect mutants) - antero-posterior pattern 0.4 % - dorso-ventral pattern 0.3 % (male-sterile mutants) ca. 2% of all genes involved in embryo pattern formation (ca. 100 of >15.000 protein-encoding genes, only 5.000 essential genes)

  14. Maternal-effect mutations Genes expressed during oogenesis (= before fertilization) or genes expressed in maternal cells (follicle) All progeny of heterozygous mother are normal. All progeny are affected only if mother is homozygous mutant Zygotic mutations Genes expressed during embryogenesis (= after fertilization) Only genetically mutant embryos are affected. (25% of progeny of heterozygous mother are affected.)

  15. Drosophila axis detemination; dorsal/ventral polarity How does the embryonic dorsal-ventral axis get translated into differentiation of different tissue types?

  16. Cell fate specification at the blastoderm stage amnio-serosa dorsal dorsal ectoderm neuro-ectoderm mesoderm ventral fate map mesoderm formation

  17. Dorsal-Ventral fate map

  18. Gurken protein specifies the Anterior-Posterior axis of the Drosophila embryo during oogenesis (Similar to EGF)

  19. Localized maternal mRNA sets up anterior and posterior poles

  20. migration of nucleus 10A 8 1-6 - + - gurken expression in the oocyte gurken expression in the oocyte Gurken also signals dorsal pole formation during oogenesis oocyte nucleus D D 10A 1-6 7 8 + - A P - V anterior posterior V follicle cells microtubules

  21. Expression of the Gurken Message and Protein Between the Oocyte Nucleus and the Dorsal Anterior Cell Membrane

  22. DORSO-VENTRAL PATTERN FORMATION follicle cells Torpedo = EGF receptor (in follicle cells) Gurken = Epidermal Growth Factor (EGF) Oocyte pipe expression X Ventral follicle cell Pipe (Golgi?) X Wind (ER?) X Nucleus mod. from van Eeden & St.Johnston

  23. Dorso-ventral pattern formation Maternal effect mutations ndl, pipe, wbl gd, snk, ea - serine proteases spz - ligand nudel, pipe, wbl dorsal RNA Toll protein Toll Tl - membrane receptor Spätzle protein Dorsal protein dorsal Zygotic mutations tube - cytoplasmic protein pelle - ser/thr protein kinase Dorsal protein amnio serosa cact - cytoplasmic inhibitor of Dorsal nuclear translocation cactus dorsal ectoderm neuro-ectoderm dorsal dl - transcription factor (morphogen) mesoderm Dl nuclear protein

  24. Dorso-ventral pattern formation dorsal dorsal mutant cactus mutant Wild type ventral A8 T1 A7 dorsalized ventralized T2 T3 A1 A2 A6 A3 A4 A5

  25. Translocation of Dorsal protein into ventral nuclei but not lateral or dorsal nuclei Wild type toll mutant cactus mutant

  26. Generation of Dorsal-Ventral Polarity in Drosophila

  27. Generation of Dorsal-Ventral Polarity in Drosophila

  28. Dorso-ventral pattern formation pivotal role of Toll pathway Inject wild-type cytoplasm into toll mutant eggs toll mutant ventral dorsalized local rescue dorsal ectoderm Wild type dorsal neuro-ectoderm (denticle belts) mesoderm polarity reversal

  29. Conserved pathway for regulating nuclear transport of transcription factors in Drosophila and mammals

  30. Cells with highest nuclear Dorsal levels become mesoderm

  31. Zygotically expressed genes

  32. Action of Dorsal protein in ventral cells

  33. Action of Dorsal protein in ventral cells High affinity for promoter, Not much Dorsal needed to activate

  34. Action of Dorsal protein in ventral cells Lower affinity for promoter, More Dorsal needed to activate

  35. Dorso-ventral pattern formation: summary nudel, pipe, windbeutel dorsal RNA Toll protein Spätzle protein Dorsal protein Dorsal protein dpp twist oocyte nucleus dorsal > repression of ventral fate in dorsal follicle cells ventral production of ligand > activation of Toll receptor > graded nuclear uptake of Dorsal morphogen > regulation of zygotic target gene expression > cell fates along DV axis

  36. Use of a similar regulatory system to pattern insects and vertebrates

  37. Patterns ectoderm in Drosophila Patterns mesoderm in vertebrates

  38. Gastrulation in Drosophila

  39. Schematic representation of gastrulation in Drosophila

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