Devo Lect 10 - Nervous system

Question 2

Main organs from ectoderm

Answer 2

Skin, pigment, brain and nerves, spinal cord

Question 3

Main organs from mesoderm

Answer 3

Bones, connective tissue, muscle, heart and blood vessels

Question 4

Main organs from endoderm

Answer 4

Gut epithelia, lungs, liver, pancreas

Question 5

Hans Spemann experiment

Answer 5

Chimera study with two dorsal blastopores, one pigmented; formed 2nd invagination, basically formed two bodies, one not pigmented except in neural tissue; transplanted section called the organizer

Question 6

Organizer

Answer 6

dorsal lip of the blastopore in amphibians; Initiates gastrulation, determines orientation; brain/neural tube forms first

Question 7

Inductive events to form nervous system

Answer 7

Formation of mesoderm: endoderm induces ectoderm to become mesoderm; chordamesoderm; endoderm releases activin; form neuroectoderm

Question 8

Chordamesoderm

Answer 8

Part of mesoderm which gets exposed to highest [activin], alters fate to form notochord

Question 9

What is activin?

Answer 9

Growth factor that activates transduction pathway; paracrine effect from endoderm to form mesoderm by binding to receptors on ectoderm cells at specific time

Question 10

Activin experiment

Answer 10

Add low concentration (.1ng/mL )forms bloodlike cells, mesenchyme; 1ng/mL forms muscle cells; 10ng/mL forms notochord; 100ng/mL forms heart muscle cells

Question 11

What receptor type does activin bind to?

Answer 11

Receptor with 3 regions (binding, transmembrane, kinase)

Question 12

Describe two engineered activin receptors

Answer 12

ActRIIBexd didn’t have an inner or transmembrane domain, freefloating. ActRIIBdn is dominant negative without kinase domain only. These are in high concentration, so they compete for activin.

Question 13

How did injection of ActRIIBexd affect levels of expression of Xbra? What is Xbra?

Answer 13

Xbra is mesodermal marker. The exd receptor blocks activin specifically, so the early expression of Xbra is delayed by about one stage, so development is abnormal (esp. anterior)

Question 14

Rescuing activin experiment

Answer 14

Injected activin mRNA, activin released and acts autocrine by binding to the normal receptors after saturating the truncated ones, higher does almost completely rescues

Question 15

Formation of neuroectoderm

Answer 15

Chordamesoderm induces cells of inner ectoderm to become neuroectoderm; this forms the neural plate, which folds to form neural tube

Question 16

Cell adhesion around neural tube

Answer 16

Epidermis has E-cadherins; neural tube cells change adhesins to N-Cad and N-CAM to fuse; neural crest cells have no adhesins

Question 17

Neurula embryo

Answer 17

An embryo that has formed the neural tube

Question 18

What is the first organ to form

Answer 18

Neural tube. Not functional yet, but still organ.

Question 19

Chordin, noggin

Answer 19

Molecules released from chordamesoderm which induce formation of neuroectoderm; are not GF; they alter function of growth factors by binding to them, ie growth factor antagonists (block BMP)

Question 20

BMP

Answer 20

bone morphogenic proteins; important cytokines in morphogenesis (originally discovered in bone and cartilage development)

Question 21

Chordin, noggin knockouts

Answer 21

If one of them knocked out: fairly normal, ears are a bit different; both knocked out: very abnormal, one eye, forebrain quite irregular; show synergy, genetic redundancy

Question 22

Human nervous system development**

Answer 22

Day 19: neural plate and chordamesoderm; D 21 (stage 9): invagination, placenta functioning; D22: neural tube, somites; D23 (stage 10): neuropores; D24: Ant. neuropore closed; D26: post. closed; D27 (stage 12): 3-5mm, pharyngeal arches, limb buds, brain forming, connecting stock (umbilical cord)

Question 23

Neuropores

Answer 23

Ant. and Post., openings of neural tube at stage 10. Ant. closes at D24, if not results in anencephaly; Post. closes at D26, if not results in spina bifida (need folic acid)

Question 24

Somites

Answer 24

Clumps of mesoderm tissue near neural tube; form the vertebrae

Question 25

Day of development and stages of development

Answer 25

Organisms develop at different rates, so we compare the stages (Carnegie stages)