Unit 12 Sea Urchin Development Review Sea Urchin Cleavage fertilization envelope large micromeres small micromeres Gilbert 10e Fig 7 3 Sea urchin cleavage review Gilbert 10e Fig 7 2 Sea Urchin Fate Map Ventral veg2 forms endoderm and secondary mesenchyme animal cells give rise to oral ventral ecotderm and aboral dorsal ectoderm Dorsal veg2 gut endoderm large micromeres micromeres give rise to skeletogenic skeletogenic primary mesoderm mesenchyme veg1 forms the base of the archenteron and ectoderm adapted from Gilbert 10e Fig 7 4 Sea Urchin Fate Map adapted from Vade Mecum 2e Sea Urchin Fate Map adapted from Vade Mecum 2e Sea Urchin Fate Map adapted from Vade Mecum 2e Sea Urchin Fate Map adapted from Vade Mecum 2e Sea Urchin Germ Layers Pluteus Aboral Oral Gilbert 10e Fig 7 12 Sea Urchin Germ Layers Pluteus Aboral Oral Gilbert 10e Fig 7 12 Asymmetries in the egg Conclusion part 1 fragments that have a nucleus and the entire animal vegetal axis are sufficient to direct normal development Kalthoff 2e Fig 8 3 Asymmetries in the egg Conclusion part 2 the vegetal half contains determinants needed for mesoderm and endoderm Kalthoff 2e Fig 8 3 Asymmetries are established early Wolpert et al 2e Fig 6 13 Asymmetries are established early Conclusion vegetal tier cells at the 8 cell stage are specified to form mesoderm and endoderm In the absence of these cells animal cells form incomplete ectoderm Wolpert et al 2e Fig 6 13 Micromeres can induce endoderm Gilbert 10e Fig 7 6 Micromeres can induce endoderm Conclusion micromeres can induce endoderm similar to an organizer Gilbert 10e Fig 7 6 Vegetal disheveled may be important for establishing vegetal fates Dishevelled is at the vegetal pole in the egg Dishevelled is at the cortex in micromeres Model dishevelled may lead to activation of b catenin Gilbert 10e Fig 7 7 Nuclear Catenin and Vegetal Fates Conclusion nuclear b catenin is at highest levels in micromeres and at intermediate levels in veg2 cells make endoderm Gilbert 910e Fig 7 7 Too much catenin leads to excessive vegetal differentiation mRNA overexpression leads to excess nuclear b catenin Gilbert 109e Fig 7 7 Too Little Catenin and Vegetal Fates Overexpression of a cadherin drives b catenin out of the nucleus Gilbert 10e Fig 7 7 Catenin and Vegetal Fates normal Conclusion b catenin is required for correct differentiation of vegetal tissues Gilbert 910e Fig 7 7 excess vegetalized blocked animalized Nodal A TGF Family Protein Nodal is an important member of the TGF b family during early development in deuterostomes It often appears to be involved in establishing left right asymmetries Gilbert 9e Fig 3 30 Nodal TGF family member is expressed in oral ectoderm nodal is initially expressed in the oral ectoderm at high levels later is it expressed on the right side adapted from Gilbert 10e Fig 7 10 Nodal patterns ectoderm and therefore mesenchyme Normal two clusters A Morpholino injected no clusters B Conclusion correct nodal expression is needed for oral aboral ventral dorsal patterning of the ectoderm Duboc et al 2004 Dev Cell 6 397 410