Devo Lect 14 - Mesoderm and Muscle Flashcards Preview

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Flashcards in Devo Lect 14 - Mesoderm and Muscle Deck (25):
1

Fig. 14.1 breakdown

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Neurula

Human embryo at day 22-25; neural tube starts developing into CNS

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4 main areas of mesoderm

Intermediate, chordamesoderm, paraxial mesoderm, lateral plate mesoderm

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Tissues from intermediate mesoderm

Kidney and gonads

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Tissues from Chordamesoderm

it forms notochord, (and Signals cells above it to form neural tube)

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Tissues from paraxial mesoderm

form the head and the somites (sclerotome, myotome, dermatome)

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Tissues from lateral plate mesoderm

Splanchnic (visceral organs etc), Somatic, Extra-embryonic

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Neural tube and notochord

Neural tube is start of spinal cord; in most vertebrates the notochord is not retained

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Formation of somites

transient segmental structures formed by compaction (day 19-20 in humans); determine number of vertebrae

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Changes in somites

Initially compacted, after a few days they break apart, forming the sclerotome, myotome, dermatome - determined by signals in environment!

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Sclerotome

From the bottom of somites; Form mainly bone and cartilage, eventually will surround the neural tube and for the vertebrae

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Myotome

forms muscles (esp. in the back region); some migrate to help form limbs

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Dermatome

Forms the dermis of the skin (esp. of back and trunk)

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Sclerotome induction

Due to sonic hedgehog from notochord (proximity)

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Myotome induction

Due to Wnt (GF) from the top of neural tube

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Dermatome induction

Due to Wnt and NT-3

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Skeletal muscle cell formation (fig 14.10)**

Myotome cell from somite, determination; dividing myoblasts multiply; cell alignment and connect, stop dividing; myotube forms, fusion (like endocytosis, receptor mediated), differentiation; maturation, contraction

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Molecules in myotome determination

GF: Wnt, Shh; express TF: MyoDm, Myf 5

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Molecules in dividing myoblasts

Fibroblast GFs (FGFs)

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Molecules in Cell alignment

Cell proteins: fibronectin, integrin, cadherin/CAM; TF: myogenin

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Molecules in myotube formation

Cell protein: Meltrin; muscle specific proteins

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MyoD

Myoblast determination protein: found only in cells with muscle linegage (in situ hybridized); Master control gene for muscle development, forms MyoD TF, turns on other genes

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Experiments with MyoD expression

MyoD in other cell types: get fibroblasts or chorion villi cells; MyoD gene transfer via virus; differentiation into myogenic cells.

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MyoD knockouts

Pretty normal! Myf5 compensates somewhat for MyoD

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Timing of mesodermal events

Stage 13, 28 days: somites changing, heart is beating; Stage 18, 44 days; bones starting to ossify; Stage 20, 50 days; spontaneous movements (muscles)