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

Dorsal-Ventral fate map Figures\Chapter09\DevBio7e09332.jpg

Genes identified in a famous screen for Drosophila mutants with embryo patterning defects Torpedo Gurken

Localized maternal mRNA sets up anterior and posterior poles Figures\Chapter09\DevBio7e09112.jpg

Gurken protein specifies the Anterior-Posterior axis of the Drosophila embryo during oogenesis Figures\Chapter09\DevBio7e09111.jpg (Similar to EGF)

Gurken also signals dorsal pole formation during oogenesis oocyte nucleus D D 10A 1-6 7 8 A + P - gurken expression in the oocyte 1-6 - anterior posterior V Gurken mRNA also relocalizes to anterior dorsal side. V follicle cells Microtubules reorient, nucleus migrates to minus end microtubules 8 gurken expression in the oocyte 10A - + -

Localization of the Gurken mRNA and protein between the oocyte nucleus and the dorsal anterior cell membrane Figures\Chapter09\DevBio7e09361.jpg

Gurken signaling inhibits production of an extracellular signal (Spätzle) by 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 cactus cact - cytoplasmic inhibitor of Dorsal nuclear translocation dorsal ectoderm neuro-ectoderm dorsal dl - transcription factor (morphogen) mesoderm Dl nuclear protein

dorsal and cactus mutants (maternal germline effect) dorsal mutant cactus mutant Wild type ventral A8 T1 T2 A7 dorsalized ventralized T3 A1 A2 A3 A4 A5 A6

Translocation of Dorsal protein into ventral nuclei but not lateral or dorsal nuclei Figures\Chapter09\DevBio7e09340.jpg Wild type toll mutant cactus mutant

Generation of Dorsal-Ventral polarity in Drosophila Figures\Chapter09\DevBio7e09351.jpg

Generation of Dorsal-Ventral Polarity in Drosophila Figures\Chapter09\DevBio7e09352.jpg

Inject wild-type cytoplasm 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 Figures\Chapter09\DevBio7e09381.jpg

Cells with highest nuclear Dorsal levels become mesoderm Figures\Chapter09\DevBio7e09382.jpg

Zygotically expressed genes Figures\Chapter09\DevBio7e09390.jpg

Action of Dorsal protein in ventral cells Figures\Chapter09\DevBio7e09400.jpg

Action of Dorsal protein in ventral cells High affinity for promoter, Not much Dorsal needed to activate Figures\Chapter09\DevBio7e09400.jpg

Action of Dorsal protein in ventral cells Lower affinity for promoter, More Dorsal needed to activate Figures\Chapter09\DevBio7e09400.jpg

Zygotically expressed genes Figures\Chapter09\DevBio7e09390.jpg

Action of Dorsal protein in ventral cells Snail repression of rhomboid creates domains with distinct gene expression patterns Figures\Chapter09\DevBio7e09400.jpg

Dorso-ventral pattern formation: summary twist dpp Dorsal protein dorsal RNA Toll protein Spätzle protein nudel, pipe, windbeutel 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

Gastrulation in Drosophila Figures\Chapter09\DevBio7e09051.jpg

Figures\Chapter09\DevBio7e09052.jpg

Schematic representation of gastrulation in Drosophila Figures\Chapter09\DevBio7e09061.jpg

Figures\Chapter09\DevBio7e09062.jpg

Figures\Chapter09\DevBio7e09053.jpg