somite derivatives: muscle and bone formation
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Somite Derivatives: Muscle and Bone Formation. Gilbert - Chapter 14. Today’s Goals. Become familiar with the mesodermal sub-populations Examine somite maturation, muscle and bone formation. Muscle and Bone Formation. Which compartment of the somite will give rise to muscle? - PowerPoint PPT PresentationTRANSCRIPT
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Somite Derivatives: Muscle and Bone Formation
Gilbert - Chapter 14
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Today’s Goals
• Become familiar with the mesodermal sub-populations
• Examine somite maturation, muscle and bone formation
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Muscle and Bone Formation
• Which compartment of the somite will give rise to muscle?
• Which compartment of the somite will give rise to bone?
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Myogenesis
• The generation of muscle cells• Come from 2 cell lineages within the
myotome– Primaxial - don’t mix with Lateral Plate
Mesoderm– Abaxial - Do mix with Lateral Plate
Mesoderm
• Muscles are induced to form by paracrine factors (ex. WNT’s, BMP’s)
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Myogenic bHLH proteins (Basic Helix Loop Helix)
• Transcription factors in MRF family (myogenic regulatory factors)
• All bind similar sites on DNA, activate muscle genes
• Expressed only in muscle cells/precursors• Sufficient to specify/commit a cell to the
muscle lineage– A variety of cells types in culture transfected with
myf-5 or myoD will become muscles
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• http://8e.devbio.com/image.php?id=155
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MyoD Expression
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Muscle cell fusion
• Muscle tissue is multinucleate
• Myoblasts (muscle precursors) fuse to form multinucleate myotubes
• At this point, cells are differentiated
• Become organized into a muscle fiber
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Differentiation of Myotubes
• In order to begin differentiation, myoblasts must stop proliferating (dividing)– Depletion of certain growth factors allows
myoblasts to exit the cell cycle and differentiate
– If growth factors are present, myoblasts will continue to proliferate
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Muscle Cell “Regeneration” in response to injury
• Muscle cells are differentiated - cannot divide to replace themselves after injury
• As in many tissues, replacement of lost tissue comes from stem cell populations associated with that tissue type
• Satellite cells - found by basement membrane of muscle fibers– Not well understood
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Bone Formation
• In vertebrates, 3 systems must form
• Craniofacial bones
• Axial Skeleton
• Appendicular Skeleton
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Anatomy of the Musculoskeletal System of Jawed Vertebrates
The locomotor anatomy is composed of 2
systems:
Axial: Vertebrae, Ribs,
Associated musculature
Appendicular: Paired appendages, Pelvic and pectoral Girdles, Associated
musculature
Must work together for an organism to function
properly.MusculatureSkeleton
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Bone formation
• 3 lineages of bone structures– Somites: axial structures (vertebrae, ribs)
• Scapula?
– Lateral plate mesoderm: appendicular structures (limbs)
• Scapula
– Cranial neural crest: craniofacial bones
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Bone Formation (Osteogenesis)
• 2 major modes
• Intramembranous (dermal) ossification
• Endochondral ossification
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Intramembranous (dermal) ossification
• Directly convert mesenchyme into bone• Involves osteoblasts, osteoclasts• Typical of skull formation
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Endochondral ossification
• Convert mesenchyme to cartilage first, then converts to bone
• Typical of the formation of vertebrate ribs, limbs
• Involves chondrocytes (make cartilage), osteoblasts (make bone)
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Zebrafish Development - Day 2
• Draw 3 embryos, label structures• Use lab printout and poster to identify
structures and stage of embryonic development
• When finished examine cleared and stained chick embryo - stained for cartilage
• Remove marbles from fish tank