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Organogenesis Encompasses : ______ ___________________________________ ___________________________________ Bio 127 - Section III ___________________________________ Organogenesis ___________________________________ Paraxial and Intermediate Mesoderm Gilbert 9e – Chapter 11 ___________________________________ ___________________________________ ___________________________________ Organogenesis Encompasses : ___________________________________ ___________________________________ • The Emergence of the Ectoderm • Neural Crest Cells and Axonal Specificity ___________________________________ • Paraxial and Intermediate Mesoderm • Lateral Plate Mesoderm ___________________________________ • Endoderm ___________________________________ ___________________________________ ___________________________________ Student Learning Objectives ___________________________________ 1. You should understand that the mesoderm forms all of the organs ___________________________________ between the ectodermal wall and the endodermal tissues. 2. You should understand that the paraxial mesoderm forms structures at the back of the embryo surrounding the spinal cord, including the ___________________________________ somites and their derivative cartilage, bone, muscle and dermis. 3. You should understand that the intermediate mesoderm forms the structures of the urogenital tract, including the kidneys, gonads, ___________________________________ ductwork and the adrenal cortex. 4. You should understand that the mesoderm helps both the ectoderm and the endoderm form their own tissues. ___________________________________ ___________________________________ ___________________________________ The mesoderm forms during gastrulation and neurulation, same as ectoderm ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Major lineages of the mesoderm ___________________________________ Somite Terminology: sclerotome: vertebral and rib cartilage myotome: muscles of back, rib cage, abdomen dermamyotome: dermal cells, limb muscle ___________________________________ syndetome: most dorsal, tendons arthrotome: most central, vertebral joints/discs, proximal ribs “unnamed”: most posterior, dorsal aorta and intervertebral arteries ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Paraxial mesoderm is made up of head mesoderm and somites ___________________________________ We’ll look closely at the somites.... ___________________________________ ___________________________________ ___________________________________ The head mesoderm forms the ___________________________________ muscles and connective tissues of the head and eyes. It even forms under the direction of different transcription factors and suffers different disease states. ___________________________________ ___________________________________ Somitogenesis ___________________________________ ___________________________________ 1. Establishment of periodicity 2. Fissure formation (separation) ___________________________________ 3. Epithelialization 4. Specification ___________________________________ 5. Differentiation ___________________________________ ___________________________________ ___________________________________ Somitogenesis: Periodicity ___________________________________ ___________________________________ Every 90 minutes in chick Periodic (less exact in mice) formation of somites Total of 50 in chick ___________________________________ is inherant 65 in mice to the cells 500 in snakes of the Notch and Wnt signals ___________________________________ mesoderm oscillate like a clock FGF signals sweep rostral-to-caudal in wave ___________________________________ ___________________________________ ___________________________________ Delta-Notch are expressed at presumptive boundaries ___________________________________ ___________________________________ ___________________________________ Delta-Notch dictates WHERE a somite ___________________________________ will form ___________________________________ ___________________________________ ___________________________________ Notch controls the wavelike expression of hairy1 ___________________________________ Where Notch is expressed Hairy-1 stays on long-term ___________________________________ ___________________________________ ___________________________________ ___________________________________ The posterior edge is the edge that signals separation ___________________________________ ___________________________________ Fissure Formation: Separation from unsegmented mesoderm ___________________________________ ___________________________________ The FGF wavefront sets up an oscillation in Wnt and Notch signaling as it passes ___________________________________ ___________________________________ Notch expression gives final position of Hairy-1 ___________________________________ Hairy-1 causes Ephrin expression which repels neighbors (remember how Ephrin repelled motor axons here also) ___________________________________ ___________________________________ Epithelialization of somites ___________________________________ ___________________________________ That same posterior ___________________________________ edge starts mesenchymal to epithelial ___________________________________ transition - N-cadherin ___________________________________ - rho family - actin change ___________________________________ ___________________________________ Specification of paraxial mesoderm ___________________________________ occurs early due to Hox expression.... ___________________________________ ___________________________________ ___________________________________ ___________________________________ transplants form what they would have in original position ___________________________________ ___________________________________ Determination and differentiation in somites ___________________________________ ___________________________________ • All of the cells of the somite are competent to form all of the derivative cell types ___________________________________ – cartilage, bone, muscle, tendons, dermis, vascular cells, meninges ___________________________________ • Their fate depends on their position near the neural tube, notochord, epidermis and ___________________________________ intermediate mesoderm ___________________________________ ___________________________________ Determination and differentiation in somites ___________________________________ First step is notochord induction of sclerotome ___________________________________ ___________________________________ ___________________________________ ___________________________________ Epithelial to mesenchymal transition causes them to migrate to form vertebral cartilage, leaves dermamyotome epithelium ___________________________________ ___________________________________ Determination and differentiation in somites ___________________________________ The second step is the segregation of dermamyotome ___________________________________ ___________________________________ ___________________________________ ___________________________________ Central and bilateral myotome surrounds dermatome ___________________________________ ___________________________________ Determination and differentiation in somites ___________________________________ Dermatome forms back dermis, brown fat ___________________________________ ___________________________________ ___________________________________ - Primaxial myotome forms back and intercostal muscles ___________________________________ - Abaxial myotome forms abdominal muscle, tongue, limbs - Central myotome proliferates madly and makes most cells ___________________________________ ___________________________________ Figure 11.12 Primaxial and abaxial domains of vertebrate mesoderm (Part 2) ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ ___________________________________ Mechanisms of Tissue Formation from Somites ___________________________________ • Myogenesis: Muscle Formation ___________________________________ • Osteogenesis: Bone Formation ___________________________________ • Vascular Replacement in the Dorsal Aorta ___________________________________ • The Syndetome: Tendon Formation ___________________________________ ___________________________________ ___________________________________ Myogenesis: Muscle Formation ___________________________________ • The paraxial, abaxial and central somite ___________________________________ • Cells in the center give rise to satellite cells ___________________________________ – maybe stem cells, maybe committed progenitors – remain viable for the life of the organism – exit cell cycle upon injury and differentiate to muscle ___________________________________ • Classic skeletal muscle differentiation – paracrine signals induce MyoD, Myf-5 ___________________________________ – TFs for muscle genes and for themselves! ___________________________________ ___________________________________ Myogenesis: Muscle Formation ___________________________________ Adult muscle cells (myotubes) are large and multinucleated ___________________________________
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