Paraxial and Intermediate Mesoderm

Mesodermal Regions Into what five regions do we subdivide the mesoderm? –prechordal plate mesoderm –chordamesoderm –paraxial mesoderm (somitic dorsal) –intermediate mesoderm –lateral plate mesoderm

Mesodermal Regions

Somite Formation What substance appears to be critical to the specificaton of of somites from paraxial mesoderm?

Somite Formation Somites are formed in a periodic manner. What appears to control this periodicity?

Somite Formation What role does the Hairy1 gene play in somite formation?

Somite Formation What factors influence the conversion of developing somite from mesenchyme to a block of epithelial tissue?

Somite Formation What determines specification of somites along anterior-posterior axis?

Somite Formation What structures are formed from the somite? –cartilage of vertebrae and ribs –dermis of dorsal skin –muscles of rib cage, back, limbs, abdominal wall and tongue

Somite Formation As the somite differentiates what regions become distinctive?

Somite Formation What factors cause differentiation of sclerotome? –sonic hedgehog –Pax1 What factors are responsible for differentiation of dermatome? –neurotropin 3 –wnt1

Somite Formation What factors influence the determination of the myotome? –epaxial myoblasts – wnt1 and 3 –hypaxial myoblasts – wnt and BMP shh inhibits BMP signal from converting sclerotome to myoblasts

Somite Formation

Myogenesis What are myogenic bHLH proteins?

Osteogenesis What are the three lineages giving rise to the skeleton? –somites – axial skeleton –lateral plate mesoderm – limbs –cranial neural crest - craniofacial

Osteogenesis How is endochondrial ossification different from intramembranous ossification?

Osteogenesis What are the different stages of bone formation in endochondrial ossification?

Intermediate Mesoderm and Kidney Formation What appears to be needed for kidney formation?

Intermediate Mesoderm and Kidney Formation What are the three major stages of mammalian kidney development?

Intermediate Mesoderm and Kidney Formation How does the pronephros form? –pronephric duct forms from intermediate mesoderm –duct cells migrate caudally –anterior part of duct induces mesenchyme to form pronephric tubules

Intermediate Mesoderm and Kidney Formation How does mesonephros form? –Wolffian duct induces tubules to form from adjacent mesenchyme –as posterior tubules form anterior ones begin to regress –source of blood forming stem cells –some tubules persist in males to become vas deferens and efferent duct

Intermediate Mesoderm and Kidney Formation How does the metanephric kidney form? –in posterior part of intermediate mesoderm mesenchyme induces branching of nephric ducts uretic buds – form ureters –uretic buds induce mesenchyme to differentiate into nephrons

Intermediate Mesoderm and Kidney Formation

Interactions of Developing Kidney Specification of metanephric mesenchyme requires two sets of transcription factors –Hoxa, Hoxc, & Hoxd 11 proteins –WT1 metanephric mesenchyme can only form kidney tubules

Interactions of Developing Kidney Glial derived neurotropic factor (GDNF) causes growth of uretic buds

Interactions of Developing Kidney FGF2 and BMP7 secreted by uretic bud prevents apoptosis of mesenchymal cells Three factors from uretic bud induce mesenchymal cells to condense and form epithelial cells –FGF2 –leukemia inhibitory factor (LIF) –wnt6

Interactions of Developing Kidney Wnt4 from mesenchyme completes conversion into epithelia of nephron –autocrine factor –may also involve Lim-1 –polycystins 1 and 2 may also be involved

Interactions of Developing Kidney Several different mesenchymal signals affect branching of uretic bud –GDNF –TGFβ-1 –BMP4 –collagen XVIII