Devo Lect 14 - Osteogenesis

Question 1

Osteogenesis

Answer 1

Flat bones and long bones; some come from somite (sclerotome) - vertebrae ad ribs; some from lateral plate and migrating mensechymal cells (neural crest)

Question 2

Intramembraneous ossification

Answer 2

aka dermal bones; face and skull; BMPs; mesenchyme cells migrate, proliferate, condense (adhesion molecules!); form osteoblasts, ECM, calcium salts bind; many layers form; no marrow in these bones, capillaries get really close to living cells

Question 3

Fontanelle

Answer 3

Some gaps still present in new born skull; filled with collagen; eventually close up and form sutures; very important for birth!

Question 4

BMPs

Answer 4

bone morphogenetic proteins; growth factors; also important in early embryo%%%

Question 5

Osteoblasts

Answer 5

Bone precursor cells; secrete collagen-glycoprotein matrix (makes up most of bone) to which calcium salts bind

Question 6

Endochondral ossification

Answer 6

aka cartilage replacement; most bones; mesenchyme cells migrate, proliferate, condense; form chondrocyte; differentiate into hypertrophic chondrocytes; replaced by osteoblasts; growth plates form; solidify on outside, some spongy bone; bone marrow in the center

Question 7

Chondrocyte

Answer 7

Cartilage forming cell; secrete ECM;

Question 8

Osteoclast

Answer 8

break down old bone, recycle ..

Question 9

Calcification

Answer 9

calcium salts getting incorporated into the ECM, hardens the bone

Question 10

Growth plate

Answer 10

osteoblasts grow from the middle outward, gradually replace cartilage

Question 11

Bone marrow function

Answer 11

blood vessels needed to provide nutrition for bone maintenance; bone is living!

Question 12

Bone fracture healing

Answer 12

Heals basically in the same way bone was formed; hematoma forms: blood clot; fibrocartilaginous callus: chondrocytes form, new ECM that connects the two pieces, new blood vessels; bony callus: cartilage cells die off, replaced by osteoblasts, new bone ECM; some small deviation will be there

Question 13

PTHrP gene KO mice

Answer 13

resulted in short-limbed dwarfism, shorter bones, domed skull;

Question 14

PTHrP receptor KO mice

Answer 14

same phenotype as PTHrP KO mice: short-limbed dwarfism

Question 15

PTHrP

Answer 15

parathyroid hormone related peptide; (PTH increases calcium levels); causes proliferation of chondrocytes, allows the bones to extend

Question 16

Hedgehog gene in Drosophila

Answer 16

segment polarity gene, keep the orientation; codes for paracrine signaling GF

Question 17

Hedgehog signaling

Answer 17

Binds to Patched receptor; blocks PKA and Slimb; causes Cubitus interuptus (Ci) to be released so it can turn on genes;

Question 18

Hedgehog genes in vertebrates

Answer 18

Shh (sonic), Dhh (desert), Ihh (Indian)

Question 19

Ihh and PTHrP interaction in bone

Answer 19

PTHrP allows cells to proliferate (have receptor), expands that region; chondrocytes committed to hypertorphy make Ihh, which affects perichondrium (via Ptc and Gli) and this causes PTHrP to be released; after a few divisions the cells lose the PTHrP receptor, hypertrophy and apoptosis, osteoblasts become osteocytes and fill in

Question 20

Timing of ossification

Answer 20

Starts around stage 18, 44 days