The Derivatives of the Mesoderm

• Divisions of the Mesoderm

  1. Epimere/somatic/paraxial
  2. Mesomere/neck/intermediate
  3. Hypomere/lateral plate
• 1. Epimere/somatic/paraxial
  2. Located close to the midline of the body adjacent to the neural tube
• 1. Nephrotome
  2. Gives rise to the kidneys
• 1. Hypomere/lateral plate
  2. Gives rise to the abdominal cavity
• 1. Abdominal cavity
  2. largest hollow space in the body, containing many organs including the digestive tract, liver, and kidneys.
• TRUE OR FALSE - Neural fold event and mesomere division is simultaneous (TRUE)
• • Neural fold 
  • structure that arises during neurulation in embryonic development. 
• • Neural tube
  • Tube formed beneath the ectoderm as the neural folds come together and converge
• Splitting of hypomere

  1. Dermatome
  2. Myotome
  3. Sclerotome
• • Dermatome
  • forms the skin.
• • Myotome
  • forms the skeletal muscle.
• • Sclerotome
  • forms the vertebrae and rib cartilage.
• • Intermediate mesoderm gives rise to:
  • Kidney
  • Gonads
• • Chorda-mesoderm gives rise to:
  • Notochord
• • Paraxial mesoderm gives rise to:
  • Head 
  • Somite
  • Sclerotome
  • Syndotome
  • Myotome
  • Dermatome
  • Endothelial cells
• • Lateral plate mesoderm give rise to:
  • Splanchnic mesoderm
  • Somatic mesoderm
  • Extra-embryonic mesoderm
• SOMITE FORMATION

  • created from paraxial rod
  • divide into discrete units because of the expression of hairy genes
• Somite formation

  1. Periodicitiy
  2. Epithelialization
  3. Specification
  4. Differentiation
• • Periodicity
  • Driven by the expression of hairy genes
  • Cells initially exhibit a pole-like structure
  • Gene expression causes migration of cells upwards and anteriorly
• • Periodicity
  • Driven by the expression of hairy genes
  • Cells initially exhibit a pole-like structure
  • Gene expression causes migration of cells upwards and anteriorly
• • Epithelialization
  • caused by expression of fibronectin and cadherins which may in turn be brought about by the transcription factor, Paraxis
  • from a mass of mesenchyme: they will start to form epithelium
  • fibronectin forming a kind of mesenchyme around the cells
  • cadherins for junctions that will form between the cells
• • Epithelialization
  • caused by expression of fibronectin and cadherins which may in turn be brought about by the transcription factor, Paraxis
  • from a mass of mesenchyme: they will start to form epithelium
  • fibronectin forming a kind of mesenchyme around the cells
  • cadherins for junctions that will form between the cells
• • Specification 
  • (axial specification occurs early in development; e.g. only certain somites form ribs)
  • somites have different fates! But at they start they all look similar
  • only certain somites will form vertebrae that will have ribs
• • Specification 
  • (axial specification occurs early in development; e.g. only certain somites form ribs)
  • somites have different fates! But at they start they all look similar
  • only certain somites will form vertebrae that will have ribs
• • Differentiation within somites
  • within the somite, they will differentiate
  • myocoel: cavity
  • from being epithelium: will again start to become mesenchymal again
  • will be ready to migrate
  • migrate just to surround: give rise to vertebrate
  • surround the neural tube
  • Ventromedial somite forms the sclerotome, contributing to vertebral structures.
  • Dorsomedial and ventrolateral portions form the myotome, giving rise to muscles, including hypaxial muscles.
  • Dermatome, situated between the sclerotome and myotome, forms the dermis of the back.
• • Differentiation within somites
  • within the somite, they will differentiate
  • myocoel: cavity
  • from being epithelium: will again start to become mesenchymal again
  • will be ready to migrate
  • migrate just to surround: give rise to vertebrate
  • surround the neural tube
  • Ventromedial somite forms the sclerotome, contributing to vertebral structures.
  • Dorsomedial and ventrolateral portions form the myotome, giving rise to muscles, including hypaxial muscles.
  • Dermatome, situated between the sclerotome and myotome, forms the dermis of the back.
• Myocoel - cavity within the somite
• • Ventromedial somite

  forms the sclerotome, contributing to vertebral structures.
• • Dorsomedial and ventrolateral portions 
  • form the myotome, giving rise to muscles, including hypaxial muscles.
• Dermatome, situated between the sclerotome and myotome, forms the dermis of the back
• Paraxis - causes the epithelialization; transcription factor to express fibronectin and cadherins
• Epimere/Somites divide into

  1. Sclerotome
  2. Myotome
  3. Dermatome
• • Sclerotome
  • induced by Shh from notochord and expresses Pax 1
• • Sclerotome
  • induced by Shh from notochord and expresses Pax 1
• • Myotome
  • induced by Wnt (1,3) from dorsal neural tube for epaxial muscle pathway and BMP4 and FGF from lateral plate mesoderm for hypaxial musculature
• • Myotome
  • induced by Wnt (1,3) from dorsal neural tube for epaxial muscle pathway and BMP4 and FGF from lateral plate mesoderm for hypaxial musculature
• • Dermatome
  • induced by neurotrophin-3 (NT-3)
• • Dermatome
  • induced by neurotrophin-3 (NT-3)
• Notochord - produces Shh
• Segmental - development of the sclerotome