Lecture 5

Question 1

3 cell types after gastrulation of blastula

Answer 1

ectoderm - epidermis and nervous system
mesoderm - muscles, connective tissue, bones, blood, kidneys
endoderm - gut, lungs, pancreas, liver

Question 2

can cells usually go backwards and become different cell after gastrulation

Answer 2

no

Question 3

why are c. eligans special

Answer 3

every cell fate has been determined
each healthy adult c. eligans have exact same number of cells (959)
all develop identically
all starts from one decision for a cell to go to anterior or posterior
early decisions restrict possible fates
cell fate becomes restricted with each decision

Question 4

zygote

Answer 4

fertilized egg

Question 5

what are the 2 main ways that cell fates can be aquired

Answer 5

asymmetric division - 2 daughter cells are different, parent cell unevenly distributed some factor (ex transcription factor)
symmetric division - daughter cells are the same, recieve different signals from external factors

Question 6

how similar are daughter cells in asymmetric division

Answer 6

very similar except for factor (same DNA, same organelles)

Question 7

what 3 things are needed in parent cell for good asymmetric cell division

Answer 7

1. correct spindle microtubule alignment
2. cytokinesis
3. partitioning of cell factor

Question 8

do tissues use a combination of symmetric and asymmetric division?

Answer 8

yes

Question 9

what are the 3 types of symmetric division

Answer 9

1. lateral inhibition
2. induction by diffusible signals
3. other

Question 10

what is lateral inhibition

Answer 10

cells will act on their immediate neighbours
2 cells inhibit each other’s differentiation
some very small imbalance (like 1 extra copy of a protein) is expressed that tips the scale, amplified by molecular mechanisms and cells aquire different fates

Question 11

provide a type of lateral inhibition, the pattern it creates and an example from nature

Answer 11

delta notch signalling
isolated differentiated cells in a field of relatively undifferentiated cells
bristles/hairs on drosphila backs

Question 12

how does notch signalling work? what does active notch mean? how is it activated?

Answer 12

delta binding to notch activates notch
active notch stops differentiation and restricts delta expression
stage 1: very unstable both cells have some delta expression, activating notch in the other to limit delta expression
stage 2: 1 cell wins tug of war. one cell expresses slightly more delta, activates slightly more notch, which downregulates more delta expression in the active notch cell. first cell has no active notch so differentiates and expresses lots of delta

Question 13

how does induction by diffusible signals work? does it matter how much signal a cell recieves?

Answer 13

organizer tissue secretes a morphogen - diffusible signal (small proteins)
yes - cell needs certain amount of signal to differentiate

Question 14

what pattern comes from induction by difffusible signals?

Answer 14

lines, stripes, bands, rings (in 3D)

Question 15

does morphogen act on organizer tissue

Answer 15

no

Question 16

can there be a morphogen gradient effect on cells

Answer 16

yes

Question 17

explain the significance of the embryo transplant experiments. why wouldn’t the opposite experiment result in the opposite effect?

Answer 17

extra dorsal tissue on other side of embryo resulted in 2 signals for dorsal cells, animal developed with 2 backs
other cells were not organizer tissue

Question 18

totipotent

Answer 18

cell from fertilized egg
all powerful, can become any cell in body
usually only in first few divisions after fertilization, very rare

Question 19

pluripotent

Answer 19

can become any cell type in adult organism (everything except placenta)

Question 20

multipotent

Answer 20

after gastrulation
can still take on multiple cell fates but limited to mesoderm vs ectoderm vs endoderm

Question 21

2 main ways cells become specific

Answer 21

1. cell memory (signal early in development, remembers signal even after signal dissipates), cell responds differently to future signals because of initial signal
2. combinatorial signaling - different combinations of signals - 1 same, 1 different

Question 22

what are 2 examples of early signals that lead to cell memory

Answer 22

chromatin remodelling
transcription factors

Question 23

what is a regulatory hierarchy?

Answer 23

cells that recieve morphogens can sometimes then secrete DIFFERENT morphogens creating DIFFERENT patterns, like layering

Question 24

describe the complex patterns in frog embryos

Answer 24

multiple signals overlap vertically and horizontally leading to segmentation

Question 25

how are drosophila embryos segmented

Answer 25

transcription factors
transcriptional factors act in regulatory hierarchy
segmentation and repeats with variation (stripes -> induction by diffusible signals)

Question 26

what genes in drosphilia specify which body part will develop from each segment? how are they clustered on the chromosome?

Answer 26

different Hox genes clustered in order that they are expressed (not normal though)

Question 27

what do hox genes encode

Answer 27

transcription factors