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Developmental homology and dissociation

Developmental homology and dissociation. Homologous genes need not function in the development of homologous structures (HOX genes, Notch signaling) Expression of a homologous gene does not imply that developmental pathways are also homologous ( engrailed and metamerism)

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Developmental homology and dissociation

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  1. Developmental homology and dissociation Homologous genes need not function in the development of homologous structures (HOX genes, Notch signaling) Expression of a homologous gene does not imply that developmental pathways are also homologous (engrailed and metamerism) Homologous developmental pathways may control the development of non-homologous structures (Dll in appendages, Pax6 in the eyes) Homologous structures need not be specified by homologous genes (insect segmentation)

  2. Segmentation of the Drosophila embryo

  3. Genetic control of segmentation in Drosophila

  4. Segment polarity genes make up the bottom level of the regulatory hierarchy Segment polarity genes establish boundaries between segments and control patterning within each segment

  5. Expression of segment polarity genes is conserved in beetles… en wg Tribolium

  6. Grasshoppers en Schistocerca

  7. Myriapods en/wg Lithobius

  8. Crustaceans Artemia wg

  9. Spiders en Cupiennius salei wg The functions of en and wg in subdividing the embryo into segments appear to be conserved

  10. krusty, a gap mutants in Tribolium en

  11. Pair-rule mutants in Tribolium

  12. eve pair-rule function is conserved in beetles Chromophore-assisted laser inactivation

  13. ftz deletion does not affect segmentation in Tribolium Antennae

  14. Pair-rule gene expression in Schistocerca Drosophila Tribolium eve ftz pby

  15. even-skipped expression in Lithobius

  16. even-skipped expression in Lithobius eve/ en eve expression does not show two-segment periodicity

  17. Expression of pair-rule genes in Chelicerates primary pair-rule genes in Cupiennius paired - secondary pair-rule in Tetranychus

  18. Evolution of Arthropod segmentation - Some parts of the segmentation pathway are conserved. - There is some turnover of genes within the overall pathway - Pair-rule patterning may be a higher insect innovation

  19. Segmentation in long germ band insects • Simultaneous generation of segments • Segmentation independent of growth • - Occurs in syncytial environment

  20. Cellularization before blastoderm formation in grasshoppers Rhodamine dextran injection

  21. Segmentation in short germ band insects (Tribolium) • Sequential generation of segments • Segmentation coupled to growth • - Occurs in a cellular environment The global patterning mechanisms cannot operate in the same way as in Drosophila

  22. Maternal gradient of bicoid establishes Anterior-Posterior axis in the Drosophila embryo

  23. The roles of maternal gradients in Drosophila Gradients form from maternally deposited transcripts by diffusion or transport in a cell-free environment

  24. bicoid function is conserved in Cyclorhapha Maternal gradients in Drosophila and Megaselia RNA interference Inhibition of Bcd protein synthesis in Megaselia results in posterior duplication (an embryo with two butts…)

  25. bicoid does not exist outside higher Dipterans

  26. hunchback is a conserved component of the Anterior determination system Megaselia RNA interference Schistocerca

  27. Tribolium hunchback is correctly regulated in Drosophila Tribolium hb Tribolium hb transgene in Drosophila Some maternal system must therefore exist in beetles But how does it work without bicoid?

  28. hunchback can substitute for bicoid Making anterior hunchback stripe in the absence of bicoid

  29. In Tribolium, anterior patterning is controlled by orthodenticle and hunchback otd hb otd; hb otd is deposited maternally Removal of otd and hb eliminates anterior structures

  30. A new mechanism for a new mode of development Drosophila Tribolium bcd hb otd Maternal hb otd hb Zygotic Anterior structures Anterior structures A maternal protein gradient can only work in a syncytium bcd has taken over the ancestral functions of otd and hb ?

  31. A parasitic wasp, Copidosoma floridanum Polyembryonic development

  32. Polyembryonic development Primary morula Polymorula Secondary morulae

  33. Polyembryonic development in Copidosoma floridanum

  34. Polyembryonic development evolved independently as an adaptation to parasitism

  35. Segmentation without maternal gradients engrailed expression in Aphidius ervi

  36. Segmentation without pair-rule genes? eve eve Bracon Aphidius en

  37. How do developmental pathways diverge from a common ancestral state? • By recruitment and loss of component genes • By re-deployment of old genes in new patterns • By changing regulatory interactions between genes

  38. Somatic sex determination pathway in Drosophila Sex determination is cell-autonomous (X:A ratio or dsx expression)

  39. Somatic sex in Drosophila is controlled by a splicing cascade Establishment (X:A ratio) Maintenance (autoregulation)

  40. Regulation of downstream target genes by doublesex Yolk protein expression Genotype/sex

  41. Sex determination mechanisms in insects Y-chromosomal genes (Tipulidae, Tephritidae) Autosomal genes (Culex, Anopheles) Mobile genes (Megaselia, Musca) X:Autosome ratio (Drosophila) Genotype of the mother (Chrysomia, Sciara) Haploid/ diploid (Hymenopterans) Environmental factors (Pseudacteon)

  42. Sex determination in the medfly Ceratitis capitata (Tephritidae) Sxl Sex is controlled by a male-determining factor on the Y tra

  43. Differential splicing of transformer in Ceratitis

  44. transformer controls sexual differentiation in Ceratitis Female Male Intersexes produced by tra RNAi

  45. Sxl and dsx in Megaselia scalaris (Phoridae) Sxl dsx

  46. Sex determination in Megaselia Megaselia lacks differentiated sex chromosomes The Maleness factor is mobile and can be located on different chromosomes This can create new Y chromosomes from former autosomes

  47. Sex determination systems in Musca domestica In male-heterogametic strains, sex is determined by a single masculinizing factor (M), which can be located either on a Y chromosome, or on 4 different autosomes Some female-heterogametic strains are homozygous for M, and sex is determined by a dominant feminizing factor F Other female-heterogametic strains lack M, and sex is determined by a recessive masculinizing factor Fman In arrhenogenic strains, sex of the offspring depends on the genotype of the mother

  48. Sexually dimorphic splicing of dsx is conserved in Musca

  49. Musca doublesex expression is sexually dimorphic Somatic sex correlates with sexually dimorphic doublesex splicing, irrespective of the upstream sex determination mechanism

  50. Musca dsxF induces vitellogenin synthesis in males

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