Week 2 Flashcards
What occurs during the cleavage stage?
A series of mitotic divisions transform egg cytoplasm into many small nucleated cells called blastomeres.
What is unique about cleavage divisions?
Cleavage divisions have a unique cell cycle and result in a progressive reduction of cytoplasmic volume.
What controls the rates of cell division and blastomere distribution during cleavage?
They are generally under the control of mRNAs and proteins stored in the oocyte.
How rapid is cleavage in most species?
In most species, cleavage is very rapid.
How does the cell cycle differ in early embryos compared to somatic cells?
Early embryos lack G1 and G2 phases and are biphasic, only having S and M stages.
What role do microtubules play during cleavage?
Microtubules (tubulin) separate chromosomes.
What is the function of actin filaments during cleavage?
Actin filaments make up the contractile ring used to separate cells.
What is karyokinesis?
Karyokinesis (Mitosis) is the division of the nucleus (naryon).
How does the positioning of the mitotic spindle affect daughter blastomeres?
The positioning of the mitotic spindle determines the position of the two daughter blastomeres.
What is the relationship between the mitotic spindle and the contractile ring?
The mitotic spindle and contractile ring are always perpendicular; the orientation of the mitotic spindle determines the plane of cytokinesis.
How is cytoplasm proportioned between daughter cells?
Cytoplasm may be proportioned evenly or unevenly between daughter cells, depending on the position of the contractile ring.
What are the two types of cleavage patterns?
Cleavage patterns can be holoblastic or meroblastic.
What factors affect cleavage patterns?
Cleavage patterns are further classified depending on how yolk disposition affects the cleavage pattern.
What does the distribution of yolk determine?
It determines where cleavage can occur and the relative size of blastomeres.
What are the terms for egg poles with different yolk concentrations?
The egg pole with rich yolk is termed the vegetal pole, while the region with low yolk concentration is termed the animal pole.
What specific factors in egg cytoplasm influence cleavage?
They can influence the position and angle of the mitotic spindle and the timing of its formation.
What is asymmetric cell division?
Asymmetric cell division sets up differences between cells, as seen in the first division in C. elegans, which gives two unequal daughter cells, AB and P1.
What triggers the establishment of PAR polarity domains in C. elegans?
The establishment of PAR polarity domains is triggered by paternal centrosomes which contract the cell cortex.
What happens after cleavage?
After the end of cleavage, you get a ball of cells called a blastula, which is hollow in the middle with liquid.
How is the blastula formed?
It results from pumping ions into this space and the movement of water into it via osmotic processes.
What are triploblasts?
Organisms with three germ layers: ectoderm, mesoderm, and endoderm.
What establishes the basic body plan in development?
Conserved mechanisms that set up axes early in development.
What are the three germ layers?
Ectoderm (outer layer), mesoderm (middle layer), endoderm (inner layer).
What is the first sign of invagination during gastrulation in sea urchins?
A central inbending of cells at the center of the vegetal plate.
What is the starting point of gastrulation in sea urchins?
Bastula.
What characterizes the animal pole in sea urchins?
More rapidly dividing, less yolky cells.
What characterizes the vegetal pole in sea urchins?
Slower dividing, more yolky cells.
When is the AV axis set up in sea urchins?
Before fertilization.
What processes underlie gastrulation?
Cell movement and changes in cell shape.
What causes changes in cell shape during gastrulation?
Altering the cytoskeleton.
What role does actin play in gastrulation?
It can create a contractile network leading to apical constriction.
What is apical constriction?
Bundles of contractile filaments composed of actin and myosin contract at the outer edge of a small number of adjacent cells, creating a wedge shape.
What are cell adhesion molecules (CAMs)?
Proteins that facilitate differential cell adhesion, crucial for development.
What types of proteins are included in CAMs?
Cadherins, immunoglobulin superfamily proteins, and integrins.
How do changing patterns of CAMs affect cell arrangement?
They force cells into new arrangements.
What is the binding characteristic of cadherins?
They generally bind homophilically.
What are the effects of gastrulation?
Establishes three main layers (endoderm, mesoderm, ectoderm), sets up body plan for the future embryo, and allows for cell proliferation, differentiation, and morphogenesis.
What is key during gastrulation?
Cell specification.
