Lecture 9; Organogenesis 1 Flashcards
What are the basic principles of feotus development?
- Devision is necessary
- Movement (morphogenesis) is necessary
- Differentiating is necessary
(patterning and organogenesis)
What is patterning?
Patterning is taking cells of equal potential and turning them into different tissues
What does fetus development start with?
Fertilization
- Fusion of egg and sperm to form a diploid zygote (23+23)
- Activates cleavage divisions to form ball fo cells (morula)
Whats happening in the morula?
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.
What is formed after the divisions?
Blastocyst
What does a blastocyst consist of?
- ICM (forms embryo body)
2. Trophoblast (forms embryonic part of placenta)
What happens to the blastocyst during implantation?
Undergoes contractions and hatches from the zona pellucida allowing further growth
What forms in the implanting blastocyst?
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)
What is formed by the epiblast in contact with the hypoblast?
bi laminar germ disc
Describe the key features of the bilaminar germ disc;
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
What happens day 15 post fertilisation?
Gastrulation
What happens at the primitive streak?
Where tissue formation starts (convergance of cells = gastrulation)
Describe when and what happens in gastrulation;
- Epiblast cells converge and invaginate the primitive streak to form mesendoderm (this migrates down and towards the cranial head) displacing the hypoblast
What does the mesendoderm form during gastrulation?
Mesendoderm forms mesoderm and endoderm
endoderm dispalces hypoblast (primitive endoderm)
What does the ectoderm give rise to?
Ectoderm; Skin, neurons, pigment
What does the mesoderm give rise to?
Mesoderm; Bone, kidneys, blood, muscle
What does the endoderm give rise to?
Endoderm; Gut, liver, pancreas
Describe the potentiating potential of epiblasts;
Bipotential as they invaginate
What are the germ layers a good example of?
Patterning; these layers form different structures
What happens as the morula divides and form into 3 germ layers (gastrula)?
lineage potential decreases
i.e morula = totipotent
Gastrula = multipotent
Describe the germ layer morphogenesis of ecto and mesoderm;
- mesodermal rod forms down midline (notochord)
- Neural ectoderm folds up (brain,neural tube)
- Mesoderm forms blocks called somitesand
Describe germ layer morphoegensis (endoderm);
The germ disc forms a tube with the endoderm lining the inside.
This gives rise to the gastric system
Write some notes on comparative biology;
Genes that encode embryology are conserved across species
What specifically is common across species;
- 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
What are the principles of patterning?
Process by which embryonic cells become organised into tissues/organs
Occurs along the body axes at a global scale
Generally occurs progressively
What are the determinants of patterning;
- Signalling pathways
2. Transcription factors
What are some examples of signalling pathways in patterning;
Ligand/Receptor transduction
- Wnt, FGF, BMP, Retinoic Acid, Shh
Cell: Cell signalling
- Notch signalling
What are the basic principles; Morphogen
- 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
How does retinoic acid function?
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
What happens if the retinoic acid gradient is disturbed;
the development of the fetus is disturbed
Whats an example of morphogen;
Sonic Hedge Hog
Shh
What does Shh do?
Transcription factor that determines facial structure.
basically specific signal determines the outcome of the cell. different signal = different outcome
What exists within transcriptional factors?
Hierarchal arrangements
There are master transcription factors
Transcription factor networks
What are the types of feedback loops?
Negative and feedback loops
What can cells do to one another in terms once differentiated?
A cell that differentiates it can propagate another cells differentiation
Transcription products can inhibit other transcription factors
What an example of transcription factors can be well conserved?
Pax6
Whats an example of master regulators;
Hox genes mutations converts antenna to legs
Selector genes or master regulators
What exists between developing tissues;
One tissue (or germ layer) patterns or induces a fate in an adjacent tissue (or germ layer)
What is essential for tissue development?
Certain signal molecules must expressed or be inhibited at certain time
