exam 2- morphogens and gradients

Question 1

a morphogen is any compound or diffusible molecule that influences the ___ and ___ of cells during ___ through the formation of ___

Answer 1

movement
organization
development
a concentration gradient

Question 2

morphogens are important in the establishment of ___ in embryos

Answer 2

polarity

Question 3

can morphogens be effective at very low concentrations?

Answer 3

yes (10^-9 to 10^-11 M)

Question 4

only ___ in morphogen level is required to change gene expression and cell differentitation

Answer 4

small (2-3 fold) change

however, many morphogen gradients can have a large range (25-50 fold)

Question 5

one morphogen can result in several…

whats needed?

Answer 5

different cell types or differentiations

1. morphogen gradient
2. multiple thresholds of response to that morphogen

Question 6

in transplant experiments, tissue does what?

Answer 6

tissue maintains its identity based on origin

Question 7

in transplant experiments, reciprocal transplants develop according to…

but tissue differentiates according to…

Answer 7

final positions in “donor”

its new positional instructions (new morphogen levels)

Question 8

Frog to newt transplant experiments indicate that a ___ can drive expression, BUT only expression of genes that ___

Answer 8

morphogen gradient

the tissue contains (or of its origin)

Question 9

for a diffusible molecule to be considered a morphogen, it must be demonstrated that: (2 things)

Answer 9

1- cells respond directly to that molecule

2- the differentiation of those cells depends on the concentration of that molecule

Question 10

how does the protein nodal function as a simple morphogen?

Answer 10

nodal (morphogen) regulates the expression of other genes over a gradient like the french flag

nodal levels / other gene regulation:
- high = goosecoid
- medium = float head
- low = no-tail

Question 11

varying nodal level alters ____

Answer 11

the gradient (alters other gene expression)

Question 12

simple threshold model: bicoid is a ____ and regulates ___ (gene expression)

Answer 12

morphogen
Hunchback

Question 13

Hunchback (hb) responds to the dose of ___ protein

Answer 13

bicoid

Question 14

what concentration activates hunchback

Answer 14

concentration above threshold level activates expression of hb

• the more bicoid transcripts, the further back hb expression occurs in the embryo

Question 15

concentrations of hunchback must be ___ to be activated, but ___ to not be repressed

Answer 15

above a level
below another level

Question 16

kruppel gene expression needs threshold levels where?

Answer 16

needs threshold levels to be in the “just right” range

Question 17

bicoid + hunchback –>

Answer 17

eve (giant & kruppel)

Question 18

name the 6 mechanisms used to interpret or regulate a morphogen gradient

Answer 18

1- differential binding site affinity
2- combinatorial input
3- feed forward loop
4- positive feedback
5- cross repression
6- reciprocal repressor gradient

Question 19

differential binding site affinity

morphogen ___ in gene promoters with diff binding affinity (low or high) can cause ________

Answer 19

binding sites

gene activation or repression by a morphogen

Question 20

combinatorial input

Answer 20

additional factors, such as enhancers and repressors are needed to act in combination for gene transcription

• more than just the morphogen is required to activate

Question 21

feed forward loop

Answer 21

a simple regulatory circuit, where the morphogen X activates gene Y (transcription factor) … in turn, the product Y functions in a combinatory input mechanism with the morphogen to activate another target gene

Question 22

positive feedback is like a feed forward loop except…

Answer 22

the signal is not needed once its started

Question 23

cross repression is repression of one ___ by ___, allowing the establishment of ___

Answer 23

morphogen gradient gene by a different one

differential expression (gap, pair rule)

Question 24

two types of cross repression:

Answer 24

1- asymmetric: one gene specific represses another gene

2- symmetric: two genes, that repress each others expression

Question 25

reciprocal repressor gradient is two ____ acting in ___

Answer 25

two different gradients acting in opposition to each other

Question 26

with morphogen gradient mechanisms, is only one mechanism used at a time?

Answer 26

most well-examined morphogen gradient pathways use a combination of these mechanisms to control their target gene expression and thus development

Question 27

all of the morphogen gradient mechanisms are also affected by changes in the ___ or ____ over ___

Answer 27

gradient or morphogen over time

gradients are not static