Devo Lect 14 - Mesoderm and Muscle

Question 1

Fig. 14.1 breakdown

Answer 1

Question 2

Neurula

Answer 2

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

Question 3

4 main areas of mesoderm

Answer 3

Intermediate, chordamesoderm, paraxial mesoderm, lateral plate mesoderm

Question 4

Tissues from intermediate mesoderm

Answer 4

Kidney and gonads

Question 5

Tissues from Chordamesoderm

Answer 5

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

Question 6

Tissues from paraxial mesoderm

Answer 6

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

Question 7

Tissues from lateral plate mesoderm

Answer 7

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

Question 8

Neural tube and notochord

Answer 8

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

Question 9

Formation of somites

Answer 9

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

Question 10

Changes in somites

Answer 10

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

Question 11

Sclerotome

Answer 11

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

Question 12

Myotome

Answer 12

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

Question 13

Dermatome

Answer 13

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

Question 14

Sclerotome induction

Answer 14

Due to sonic hedgehog from notochord (proximity)

Question 15

Myotome induction

Answer 15

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

Question 16

Dermatome induction

Answer 16

Due to Wnt and NT-3

Question 17

Skeletal muscle cell formation (fig 14.10)**

Answer 17

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

Question 18

Molecules in myotome determination

Answer 18

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

Question 19

Molecules in dividing myoblasts

Answer 19

Fibroblast GFs (FGFs)

Question 20

Molecules in Cell alignment

Answer 20

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

Question 21

Molecules in myotube formation

Answer 21

Cell protein: Meltrin; muscle specific proteins

Question 22

MyoD

Answer 22

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

Question 23

Experiments with MyoD expression

Answer 23

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

Question 24

MyoD knockouts

Answer 24

Pretty normal! Myf5 compensates somewhat for MyoD

Question 25

Timing of mesodermal events

Answer 25

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