The egg Polarities are established along anterior- 29.3 A gradient must be posterior(head-tail)axis and dorsal-ventral (back-abdomen) Dorsal converted into discrete Anteri Posterior compartments Ventral The larva Mouth parts are at anterior,tail parts at Figure 29.1 Gradients in the posterior.Bands of denticles extend from the ventral side,and identify segmentation units along the anterior-posteror axis egg are translated into segments on the anterior- posterior axis and into Mouth Tai Denticles specialized structures on the Adult fly dorsal-ventral axis of the Segmented structure has 3 thoracic segments &8 abdominal segments larva,and then into the segmented structure of the adult fly. 清苇大当 Thorax Abdomen
Figure 29.1 Gradients in the egg are translated into segments on the anteriorposterior axis and into specialized structures on the dorsal-ventral axis of the larva, and then into the segmented structure of the adult fly. 29.3 A gradient must be converted into discrete compartments
Fertilized egg has two nuclei 29.3 A gradient must be converted into discrete Divisions 1-8(90 min) Nuclei divide in common cytoplasm compartments (syncytium).Nuclei in polar plasm(pink) become gem cell precursors. Figure 29.2 The early Syncytial blastoderm (150 min) Nuclei migrate to periphery and divide;4 further divisions occur(in close but not development of the perfect synchrony). Drosophila egg occurs in a common cytoplasm until the ●●●●●●果●e甲色●e stage of cellular blastoderm. Cellular blastoderm (195 min) Membranes surround nuclei to form monolayer of ~6000 somatic cells. 情華大当
Figure 29.2 The early development of the Drosophila egg occurs in a common cytoplasm until the stage of cellular blastoderm. 29.3 A gradient must be converted into discrete compartments
29.4 Maternal gene products establish gradients in early embryogenesis Morphogen is a factor that induces development of particular cell types in a manner that depends on its concentration. 清菜大当
Morphogen is a factor that induces development of particular cell types in a manner that depends on its concentration. 29.4 Maternal gene products establish gradients in early embryogenesis
29.4 Maternal gene products establish gradients in early embryogenesis Follicle cells Oocyte Nurse cells Cytoplasmic bridge Figure 29.3 A Drosophila follicle contains an outer surface of follicle cells that surround nurse cells that are in close contact with the oocyte.Nurse cells are connected by cytoplasmic bridges to each other and to the anterior end of the oocyte.Follicle cells are somatic;nurse cells and the oocyte are germline in origin. 清菜大当
Figure 29.3 A Drosophila follicle contains an outer surface of follicle cells that surround nurse cells that are in close contact with the oocyte. Nurse cells are connected by cytoplasmic bridges to each other and to the anterior end of the oocyte. Follicle cells are somatic; nurse cells and the oocyte are germline in origin. 29.4 Maternal gene products establish gradients in early embryogenesis
29.4 Maternal gene products establish gradients in early embryogenesis Anterior Posterior Teminal Dorsovertral Matemal scmatic 38/ windibeute! Matemal germline exuperantie capuccino gastrlstion-defective ider mago nashi atz光 Zygotictargets 农e2en emp的y spraces Figure 29.4 Each of the four maternal systems that functions in the egg is initiated outside the egg.The pathway is carried into the egg,where each pathway has a localized product that is the morphogen.This may be a receptor or a regulator of gene expression.The final component is a transcription factor,which acts on zygotic targets that are responsible for the next stage of development. 清菜大兰
Figure 29.4 Each of the four maternal systems that functions in the egg is initiated outside the egg. The pathway is carried into the egg, where each pathway has a localized product that is the morphogen. This may be a receptor or a regulator of gene expression. The final component is a transcription factor, which acts on zygotic targets that are responsible for the next stage of development. 29.4 Maternal gene products establish gradients in early embryogenesis