Signalling molecules

Question 1

Morphogen definition

Answer 1

A molecule that diffuses to form a gradient and has different effects on the cell depending on the concentration

Question 2

Sonic Hedgehog functions

Answer 2

1. Secreted in Zone of polarising activity- leading to anterior posterior patterning of the limb
2. Secreted by notochord- instructing cells of the neural tube to form a floor plate
3. leads to the production of different neurons- as the neural tube is dorsoventrally patterned
4. somitogenisis
5. formation of median hinge point

Question 3

Wnt signalling pathway definition

Answer 3

Group of signal transduction pathways which begin with proteins that pass signals to cells via cell surface receptors

Question 4

Wnt functions

Answer 4

1. Primitive streak produces Wnt which establishes the posterior region during late gastrula
2. Wnt Beta induces the formation of the Spemann Organiser
3. High Wnt signalling in dorsal region of neural tube- opposite to Shh
4. trunk neural crest cell proliferation

Question 5

Bmp definition

Answer 5

Bone morphogenic factor- Group of growth factors known as cytokines and metabologens, which are important in inducing the formation of bone and cartilage

Question 6

Bmp Functions

Answer 6

1. BMP-4 signals ectoderm to develop into skin cells overlying the mesoderm
2. Underlying mesoderm blocks the action of BMPP-4 to allow ectoderm to continue neural development
3. BMP-4 gradient produced in neural tube, in same region as Wnt

Question 7

Examples of BMP inhibitors

Answer 7

Noggin and Chordin

Question 8

Noggin function

Answer 8

1. Involved in somite patterning
2. released from notochord and inhibits TGF betas, such as BMP4- allowing the neural tube to be patterned
3. Noggin activity in mesoderm forms cartilage, bone and muscle growth

Question 9

Notch protein function

Answer 9

1. coordinates cell clocks, enabling segmentation of somites

Question 10

Fibroblast growth factors function

Answer 10

1. FGF10 produced in lateral plate mesoderm in limb bud in proliferating zone. - induces formation of AER
2. FGF8 produced in apical ectodermal ridge-create a positive feed back loop- more FGF10- longer limbs
3. coordinates cell clock in somitogenesis

Question 11

Homeobox definition

Answer 11

A DNA sequence, around 180 bp long, found within genes that are involved in the regulation of morphogenesis

Question 12

2 main types of homeobox genes

Answer 12

HOX and PAX

Question 13

Explain functions of HOX

Answer 13

1. HoxA and HoxD specific segment identify along the limb axis

Question 14

Explain functions of PAX

Answer 14

1. Embryo segmentation and nervous system development
2. PAX7- dermamyotome becomes myotome
3. PAX3- dermamyotome hypaxial and epaxial become myotome involved in myogeneifss