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Drosophila dorsal/ventral axis detemination. How are different tissue types specified at distinct positions on the embryonic dorsal-ventral axis?. Cell fate specification at the blastoderm stage. amnio-serosa. dorsal. dorsal ectoderm. neuro-ectoderm. mesoderm. ventral. fate map.
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Drosophila dorsal/ventral axis detemination How are different tissue types specified at distinct positions on the embryonic dorsal-ventral axis?
Cell fate specification at the blastoderm stage amnio-serosa dorsal dorsal ectoderm neuro-ectoderm mesoderm ventral fate map mesoderm formation
Genes identified in a famous screen for Drosophila mutants with embryo patterning defects Torpedo Gurken
Localized maternal mRNA sets up anterior and posterior poles
Gurken protein specifies the Anterior-Posterior axis of the Drosophila embryo during oogenesis (Similar to EGF)
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
Expression of the Gurken Message and Protein Between the Oocyte Nucleus and the Dorsal Anterior Cell Membrane
Gurken signaling inhibits production of an extracellular signal (Spätzle) by follicle cells 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 modified from van Eeden & St.Johnston
Maternal effect mutations in dorso-ventral patterning Somatic (follicle cells) ndl, pipe, wbl gd, snk, ea - serine proteases Spätzle spz - ligand Germline (nurse cells) nudel, pipe, wbl dorsal RNA Toll protein Spätzle protein Dorsal protein Toll Tl - membrane receptor 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
dorsal and cactus mutants (maternal germline effect) dorsal dorsal mutant cactus mutant Wild type ventral A8 T1 A7 dorsalized ventralized T2 T3 A1 A2 A6 A3 A4 A5
Translocation of Dorsal protein into ventral nuclei but not lateral or dorsal nuclei Wild type toll mutant cactus mutant
The Toll pathway in dorso-ventral pattern formation 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
Conserved pathway for regulating nuclear transport of transcription factors in Drosophila and mammals
Action of Dorsal protein in ventral cells High affinity for promoter, Not much Dorsal needed to activate
Action of Dorsal protein in ventral cells Lower affinity for promoter, More Dorsal needed to activate
Action of Dorsal protein in ventral cells Snail repression of rhomboid creates domains with distinct gene expression patterns
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
Use of a similar regulatory system to pattern insects and vertebrates
Patterns ectoderm in Drosophila Patterns mesoderm in vertebrates
3 head The fly body plan: each segment has a unique identity and produces distinctive structures 3 thorax 8 abdomen
Mutations affecting the antero-posterior axis 3 independent maternal systems: anterior, posterior, terminal fate map larva triple mutants active active systems systems APT --- wild-type single mutants double mutants -PT -P- anterior bicoid A-T --T posterior oskar AP- A-- terminal torso additive phenotypes
bicoid mutant phenotype Embryo from wild-type mother Embryo from bicoid mother
Anterior: bicoid is required for head and thorax bicoid mutant Wild type blastoderm fate map head abdomen + thorax abdomen
Bicoid mRNA localization in embryo (tethered to microtubules)
Nuclei divide without cell division in Drosophila to produce a syncytial blastoderm embryo Fig. 9.1
Bicoid protein gradient in syncytial blastoderm embryo - diffuses after translation from localized mRNA - protein unstable