Cleavage Flashcards
What is the life cycle of a mouse?
cleavage-implantation-gastrulation-turning-organogenesis-fetal growth and development-birth
What are some features of cleavage division of Xenopus?
1st divisions are extremely rapid Synchronous Numbers increase logarithmically No growth- cells get smaller 12 divisions= 4000 cells
Properties of cleavage
- Splits the single cell of the fertilised egg into 100s.
- Cell division is normally synchronous.
- Division leads to smaller cells as no growth occurs.
- Modified cell cycle to allow quick divisions (no G phase).
- Dependent upon proteins and mRNA stored in the fertilised egg (mRNA given by the mother).
Do patterns of cleavage influence development and how are the patterns controlled?
No. Controlled by the yolk.
What are some of the patterns of cleavage?
Radial: amphibians, thin yolk
Discoidal: thick yolk
Bilateral: synchronous division on both sides of the plane of symmetry
Superficial: Drosophila, thick yolk is in the middle.
Where does spiral cleavage occur and in what direction does it go?
Occurs in snails. Goes up-left (clockwise) and up-right (anticlockwise).
What is the direction of coiling determined by?
Maternal genotype. Right coiling mother mixed with left coiling father will give right coiling offspring and vice versa.
What are the features of mammalian cleavage?
- Cleavage divisions are much slower
- Divisions are not synchronous.
- The plane of cleavage can differ between cells in the same division cycle (rotational cleavage).
- Development is driven by zygotic genes so they have a standard cell cycle and can produce its own mRNA.
- Mammalian embryos undergo compaction (change in shape of the embryo after the 8 or 16 cell embryo formation).
What does cell division look like after cleavage?
Division is no longer synchronous.
It occurs in patches where, in that area, it is still synchronous.
Groups that divide together make the same organ/system.
Patches go through 2 or 3 divisions- not more.
Why do cells need zygotic expression and what protein is important in the correct functioning of the divisions?
Zygotic expression is needed to keep the cell going through the cell cycle otherwise you have too few cells.
String protein is important because absence of it causes the cell to arrest in G2 phase.
What does the string protein do?
Encodes the Drosophila homologue of Cdc25 which regulates CDK1 activity.
String= Cdc25 basically so if inhibited CDK1 stays inactivated so it can’t stimulate Histone1, MAP, Lamins etc so the cell doesn’t move further in the cell cycle.
What does Histone1, MAP and Lamins do?
Histone1-chromosome condensation.
MAP-spindle formation
Lamin-nuclear envelope breakdown
How is zygotic expression initiated and where?
Initiated at the mid blastula transition by changing the ratio of nuclei to cytoplasm.
