Chapter 29 Gradients, cascades and signaling pathways 莘大
Chapter 29 Gradients, cascades, and signaling pathways
29.1 Introduction 29.2 Fly development uses a cascade of transcription factors 29.3 A gradient must be converted into discrete compartments 29. 4 Maternal gene products establish gradients in early embryogenesis 29.5 Anterior development uses localized gene regulators 29.6 Posterior development uses another localized regulator 29.7 How are mRNAS and proteins transported and localized? 29.8 Dorsal-ventral development uses localized receptor-ligand interactions 29.9TGFb/BMPS are diffusible morphogens 29. 10 Cell fate is determined by compartments that form by the blastoderm stage 29. 11 The wingless/wnt signaling pathway 29. 12 Complex loci are extremely large and involved in regulation 29. 13 The homeobox is a common coding motif in homeotic genes 消当
29.1 Introduction 29.2 Fly development uses a cascade of transcription factors 29.3 A gradient must be converted into discrete compartments 29.4 Maternal gene products establish gradients in early embryogenesis 29.5 Anterior development uses localized gene regulators 29.6 Posterior development uses another localized regulator 29.7 How are mRNAs and proteins transported and localized? 29.8 Dorsal-ventral development uses localized receptor-ligand interactions 29.9 TGFb/BMPs are diffusible morphogens 29.10 Cell fate is determined by compartments that form by the blastoderm stage 29.11 The wingless/wnt signaling pathway 29.12 Complex loci are extremely large and involved in regulation 29.13 The homeobox is a common coding motif in homeotic genes
29.1Introduction Development begins with a single fertilized egg, but gives rise to cells that have different developmental fates. The problem of early development is to understand how this asymmetry is introduced how does a single initial cell give rise within a few cell divisions to progeny cells that have different properties from one another? The means by which asymmetry is generated varies with the type or organism. The egg itself may be homogeneous, with the acquisition of asymmetry depending on the process of the initial division cycles as in the case of mammals. Or the egg may have an initial asymmetry in the distribution of its cytoplasmic components, which in turn gives rise to further differences as development proceeds, as in the case of drosophila 消当
Development begins with a single fertilized egg, but gives rise to cells that have different developmental fates. The problem of early development is to understand how this asymmetry is introduced: how does a single initial cell give rise within a few cell divisions to progeny cells that have different properties from one another? The means by which asymmetry is generated varies with the type of organism. The egg itself may be homogeneous, with the acquisition of asymmetry depending on the process of the initial division cycles, as in the case of mammals. Or the egg may have an initial asymmetry in the distribution of its cytoplasmic components, which in turn gives rise to further differences as development proceeds, as in the case of Drosophila 29.1 Introduction
29.1Introduction Development begins with a single fertilized egg, but gives rise to cells that have different developmental fates. The problem of early development is to understand how this asymmetry is introduced how does a single initial cell give rise within a few cell divisions to progeny cells that have different properties from one another? The means by which asymmetry is generated varies with the type or organism. The egg itself may be homogeneous, with the acquisition of asymmetry depending on the process of the initial division cycles as in the case of mammals. Or the egg may have an initial asymmetry in the distribution of its cytoplasmic components, which in turn gives rise to further differences as development proceeds, as in the case of drosophila 消当
Development begins with a single fertilized egg, but gives rise to cells that have different developmental fates. The problem of early development is to understand how this asymmetry is introduced: how does a single initial cell give rise within a few cell divisions to progeny cells that have different properties from one another? The means by which asymmetry is generated varies with the type of organism. The egg itself may be homogeneous, with the acquisition of asymmetry depending on the process of the initial division cycles, as in the case of mammals. Or the egg may have an initial asymmetry in the distribution of its cytoplasmic components, which in turn gives rise to further differences as development proceeds, as in the case of Drosophila 29.1 Introduction
29.2 Fly development uses a cascade of transcription factors Homeotic genes are defined by mutations that convert one body part into another, for example, an insect leg may replace an antenna Segmentation genes are concerned with controlling the number or polarity of body segments in insects 消当
Homeotic genes are defined by mutations that convert one body part into another; for example, an insect leg may replace an antenna. Segmentation genes are concerned with controlling the number or polarity of body segments in insects. 29.2 Fly development uses a cascade of transcription factors
Polant es are established along anterior- 29.3A gradient must be posterior (head-tail) axis and dorsal-ventral (back-abdomen) converted into discrete Enteric Posterior compartments Ventral he larva Mouth parts are at antenor, tail parts at Figure 29. 1 Gradients in the postenior. Bands of denticles extend from the ventral side, and identify segmentation units egg are translated into along the anterior-postenor axis segments on the anterior posterior axis and into Mouth 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 消当 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
has two nuclei 29.3A gradient must be converted into discrete Divisions 1-8(90 min Nuclei divide in common cytoplasm compartments (syncytium). Nuclei in pol ar plasm(pink) become germ cell precursors Figure 29. 2 The early Syncytial blastoderm(150 min) Nuclei migrate to penphery and divide: 4 further divisions occur(in close but not development of the perfect synchrony) ●eeo● Drosophila egg occurs in a common cytoplasm until the stage of cellular blastoderm Cellular blastoderm(195 min) Membranes surround nuclei to form monolayer of -6000 somatic cells eeeeekceEa 消当
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 消当
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 esta blish gradients in early embryogenesis Follicle cells Oocyte Q 何g9 W urse cell CytoplasmIc bndge 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 请莘大
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 esta blish gradients in early embryogenesis Anterior Posterior Teminal Dorsoventral Matemal somatic torsowke Matemal germline exuperante capwocino trunk gastraston-defeftie identi polehole easter mago nash spatzle Zygotictargets hunchback knops puckebein decapentapfeg 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 请莘大
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