Lecture 6: What controls development in animals

Question 1

Key stages of development (reviewed)

Answer 1

• fertilisation
• cleavage
• Gastrulation
• organogenesis
• morphogenesis

Question 2

morphogenesis:

Answer 2

cell differentiation and growth to form the complex adult shape

Question 3

development is controlled by:

Answer 3

• the cytoplasm
• genes
• the external environment

Question 4

Nuclear DNA does 2 things:

Answer 4

• replicates itself

- makes proteins (by transcription of RNA)

Question 5

what controls early embryonic development?

Answer 5

• Nuclear DNA replication
• Enzymes and proteins are provided by the cytoplasm
• Metabolic cycles and instructions for driving cell division are controlled by the cytoplasm
• Zygotic cytoplasm comes from the mother, so early development is under maternal control

Question 6

Genomic activation is the

Answer 6

transition from eternal control to embryo control

Question 7

the timing of genomic activation…

Answer 7

VARIES

• pigs & rats: 4-8 cell embryo
• humans & cattle: 8 cell embryo
• frogs: 3,000-4,000 cell embryo

Question 8

differentiation is the…

Answer 8

commitment of a cell to a particular fate, prior to this, cells are totipotent

Question 9

differentiation results from..

Answer 9

differential gene expression.

-differential gene expression is influenced by the cytoplasm & the extracellular environment

Question 10

Developmental control: the cytoplasm

Answer 10

• no information is lost in the early stages of embryonic development (genomic equivalence)
• the cytoplasm controls the fate of the nucleus
• cytoplasmic factors in the gray crescent are necessary for development

Question 11

chemical single are involved in cell differentiation:

Answer 11

1) CYTOPLASMIC SEGREGATION - a factor is unequally distributed in the cytoplasm and ends up in some daughter cells but not others
2) INDUCTION - a factor is secreted by some cells to induce other cells to differentiate

Question 12

cytoplasmic segregation:

Answer 12

• Dividing cells receive unequal amounts of materials that were distributed unevenly in the zygote
• These differences in cytoplasmic make-up cause differentiation of cells

Question 13

(primary) induction: in amphibians

Answer 13

cells movie over the dorsal lip of the blastopore (Spemann organiser) induce overlying ectoderm to form neural tissue

Question 14

(primary) induction: in birds

Answer 14

cells moving over Hensons node are induced to form the Central Nervous System

Question 15

(secondary) induction in the vertebrate eye

Answer 15

• developing forebrain and surface tissue work together
• surface tissue expands forms lens placode tissue
• -optic cup formed from developing forebrain, developing lens folds inside optic cup
• developing sense forms a circle = LENS + cornea lies over top

Question 16

how do cells ‘know’ where they are in an animal

Answer 16

by interpreting POSITIONAL INFORMATION

Question 17

positional information is given by..

Answer 17

the concentration gradient of a morphogen

Question 18

a signal is considered to be a morphogen if//

Answer 18

• it directly affects target cells

- different concentration cause different effects

Question 19

in hands: morphogen concentration and fingers & thumbs

Answer 19

• the cells that become the bones & muscles of a limb receive positional information, then organise appropriately.
• Cells at the base of the bud make a morphogen (BMP2) whose gradient determines the anterior–posterior axis of the limb
• highest dose of BMP2 > thumb
• smallest dose of BMP2 > little finger

Question 20

morphogen in hands

Answer 20

BMP2

Question 21

what is genomic imprinting:

Answer 21

In mammals, some development genes are active only if they come from a sperm, others only if they come from an egg.

• -male-male zygotes don’t produce an embryo
• -female-female zygotes don’t form a placenta

Question 22

Prader-Willli Syndrome:

Answer 22

deletion on paternal chromosome 15

Question 23

Angelman Syndrome

Answer 23

Deletion on maternal chromosome 15

Question 24

Segmentation genes: what and how many

Answer 24

• influence the number, boundaries & polarity of the body segments
• 4

Question 25

segmentation gene:

gap genes

Answer 25

-organise large areas along the anterior-posterior axis

Question 26

segmentation gene: pair rule genes

Answer 26

divide the embryo into units of two segments each

Question 27

segmentation gene: segment polarity genes

Answer 27

determine segment boundaries

Question 28

segmentation gene: homeotic genes

Answer 28

are exposed along the length of the body & determine what the segment will become

Question 29

control of body segmentation (in mice)

Answer 29

4 families of homeotic genes, called Hox genes, control differentiation along the body axis

Question 30

homeotic genes:

Answer 30

specify the properties of each segment, mutations in these genes change the segments identity

Question 31

apoptosis is

Answer 31

programmed cell death, caused by activation of “death” genes

Question 32

apoptosis in human embryos

Answer 32

they have webbed hands & feet, the enzyme Caspase stimulates apoptosis

Question 33

C. elegans has 1090 somatic cells,___ are programmed to die

Answer 33

131

Question 34

environmental influence on development (mice)

Answer 34

Sometimes an environmental factor is necessary for successful development

• house mice raised in microbe-free environments lack gut bacteria
• gut bacteria induce gene expression in the intestine, which is essential for normal capillary development

Question 35

neurulation refers

Answer 35

to the folding process in vertebrate embryos, which includes the transformation of the neural plate into the neural tube

Question 36

neurulation is primarily under__

Answer 36

genetic control but environmentally derived material in the form of vitamins and mineral are also needed

Question 37

in humans, failure of the neural tube to close at the posterior ends results in

Answer 37

spina bifida

Neural tube defects can be reduced if pregnant women receive adequate folic acid.

Question 38

in humans, failure of the neural tube to close at the anterior end result in

Answer 38

anencephaly

Neural tube defects can be reduced if pregnant women receive adequate folic acid.

Question 39

lack of iodine in the diet causes

Answer 39

• goitre in adults
• cretinism in babies

simple iodine supplements or injections result in healthy babies

Question 40

can environemtla factors disrupt development?

Answer 40

YES

• Cyclopamine, found in the corn lily plant, causes birth defects in lambs
• Cyclopamine inhibits the action of the Sonic Hedgehog protein, which is involved in the formation of the neural system