Lecture 9; Organogenesis 1

Question 1

What are the basic principles of feotus development?

Answer 1

• Devision is necessary
• Movement (morphogenesis) is necessary
• Differentiating is necessary
  (patterning and organogenesis)

Question 2

What is patterning?

Answer 2

Patterning is taking cells of equal potential and turning them into different tissues

Question 3

What does fetus development start with?

Answer 3

Fertilization

• Fusion of egg and sperm to form a diploid zygote (23+23)
• Activates cleavage divisions to form ball fo cells (morula)

Question 4

Whats happening in the morula?

Answer 4

The division of a zygote is exponential

• day 1 = 2 cell
• day 2 = 4 cell
• day 3 = 16 cell (morula)

Each cell at this stage is known as a blastomere, surrounded by zona pullucida

• Process is also known as a reduction of devision as each cell is reduced in volume.

Question 5

What is formed after the divisions?

Answer 5

Blastocyst

Question 6

What does a blastocyst consist of?

Answer 6

1. ICM (forms embryo body)

2. Trophoblast (forms embryonic part of placenta)

Question 7

What happens to the blastocyst during implantation?

Answer 7

Undergoes contractions and hatches from the zona pellucida allowing further growth

Question 8

What forms in the implanting blastocyst?

Answer 8

ICM divides into epiblast and hypobalst

• epiblast forms tube, top half becomes amniotic cells contributing to the amnioctic cavity, bottom half forms the embryo proper
• hypoblast froms yolk sac (primitive nutrient source)

Question 9

What is formed by the epiblast in contact with the hypoblast?

Answer 9

bi laminar germ disc

Question 10

Describe the key features of the bilaminar germ disc;

Answer 10

bilaminar germ disc; floor of amniotic cavity;epiblast and roof of yolk sac; hypoblast

• The disc has a primitive streak in the caudal-cranial plane + primitive opening that forms mouth-pharynx junction

Question 11

What happens day 15 post fertilisation?

Answer 11

Gastrulation

Question 12

What happens at the primitive streak?

Answer 12

Where tissue formation starts (convergance of cells = gastrulation)

Question 13

Describe when and what happens in gastrulation;

Answer 13

• Epiblast cells converge and invaginate the primitive streak to form mesendoderm (this migrates down and towards the cranial head) displacing the hypoblast

Question 14

What does the mesendoderm form during gastrulation?

Answer 14

Mesendoderm forms mesoderm and endoderm

endoderm dispalces hypoblast (primitive endoderm)

Question 15

What does the ectoderm give rise to?

Answer 15

Ectoderm; Skin, neurons, pigment

Question 16

What does the mesoderm give rise to?

Answer 16

Mesoderm; Bone, kidneys, blood, muscle

Question 17

What does the endoderm give rise to?

Answer 17

Endoderm; Gut, liver, pancreas

Question 18

Describe the potentiating potential of epiblasts;

Answer 18

Bipotential as they invaginate

Question 19

What are the germ layers a good example of?

Answer 19

Patterning; these layers form different structures

Question 20

What happens as the morula divides and form into 3 germ layers (gastrula)?

Answer 20

lineage potential decreases

i.e morula = totipotent

Gastrula = multipotent

Question 21

Describe the germ layer morphogenesis of ecto and mesoderm;

Answer 21

• mesodermal rod forms down midline (notochord)
• Neural ectoderm folds up (brain,neural tube)
• Mesoderm forms blocks called somitesand

Question 22

Describe germ layer morphoegensis (endoderm);

Answer 22

The germ disc forms a tube with the endoderm lining the inside.

This gives rise to the gastric system

Question 23

Write some notes on comparative biology;

Answer 23

Genes that encode embryology are conserved across species

Question 24

What specifically is common across species;

Answer 24

• Style of cleavage and gastrulation differ
• At segmentation stage, vertabrate embryos are similar
• morphological changes occur later in later fetal life i.e face development

Question 25

What are the principles of patterning?

Answer 25

Process by which embryonic cells become organised into tissues/organs

Occurs along the body axes at a global scale

Generally occurs progressively

Question 26

What are the determinants of patterning;

Answer 26

1. Signalling pathways

2. Transcription factors

Question 27

What are some examples of signalling pathways in patterning;

Answer 27

Ligand/Receptor transduction

• Wnt, FGF, BMP, Retinoic Acid, Shh

Cell: Cell signalling
- Notch signalling

Question 28

What are the basic principles; Morphogen

Answer 28

• A signalling molecule acts directly on cells to produce specific cellular responses that are dependant on concentration
  i. e on cell could form three different cell types, but what it ends up as is determined by the concentration

Question 29

How does retinoic acid function?

Answer 29

There is a gradient of retinoic acid in the developing embryo i.e at specific parts the concentration is higher or lower

This drive signalling pathways that activate transcription pathways

Question 30

What happens if the retinoic acid gradient is disturbed;

Answer 30

the development of the fetus is disturbed

Question 31

Whats an example of morphogen;

Answer 31

Sonic Hedge Hog

Shh

Question 32

What does Shh do?

Answer 32

Transcription factor that determines facial structure.

basically specific signal determines the outcome of the cell. different signal = different outcome

Question 33

What exists within transcriptional factors?

Answer 33

Hierarchal arrangements

There are master transcription factors

Transcription factor networks

Question 34

What are the types of feedback loops?

Answer 34

Negative and feedback loops

Question 35

What can cells do to one another in terms once differentiated?

Answer 35

A cell that differentiates it can propagate another cells differentiation

Transcription products can inhibit other transcription factors

Question 36

What an example of transcription factors can be well conserved?

Answer 36

Pax6

Question 37

Whats an example of master regulators;

Answer 37

Hox genes mutations converts antenna to legs

Selector genes or master regulators

Question 38

What exists between developing tissues;

Answer 38

One tissue (or germ layer) patterns or induces a fate in an adjacent tissue (or germ layer)

Question 39

What is essential for tissue development?

Answer 39

Certain signal molecules must expressed or be inhibited at certain time