16 Flashcards
What is the difference between the bilaminar and trilaminar disc in amniotes?
Bilaminar: epi and hypoblast
Trilaminar: ecto, meso, endo
What layer does the embryo come from?
The epiblast
How is the trilaminar germ disc formed?
Epiblast cells migrate through the primitive streak to form the endo and mesoderm, the non-ingressed cells are the ectoderm.
What is the role of the zona pellucida in pregnancy?
It prevents early implantation before reaching the uterus.
What are the two cleavage patterns?
Radial: Parallel or perpendicular cleavage to the cell’s polar axis, results in symmetrically aligned cells
Rotational: A symmetrical first cell division followed by an asymmetric second cell division results in rotational and uneven cell arrangement
What cleavage patterns do mammals have?
Rotational
How is fluid attracted into the developing embryo?
Positive polarization through sodium pumps.
Why does asymmetric meiosis occur prior to fertilization?
Because the egg is a polar body.
What causes the shift between asymmetric meiosis and symmetric mitosis?
Maternal effect genes.
What is the role of Mater in embryonic development?
It’s a MEG. It’s a haplosufficient gene. Homozygous knock out females are sterile, all else fertile. They’re sterile because the cells never transition to symmetric division and die at the 2 cell stage during pre-implantation development.
What MEGs are part of the subcortical maternal complex? What is their role?
FLOPED, MATER, Filia, TLE6. All these if mutated also cause asymmetrical cleavage similar to Mater. They control symmetric division of mouse zygotes by regulating F-actin, and are required for the transition from asymmetrical to symmetrical division.
What is Kartagener syndrome? How are the symptoms connected?
Reversed left-right asymmetry of the organs (situs inversus) 50% of the time, and always chronic bronchitis and male sterility (mutation in motor proteins of sperm)
Cilia and sperm tails are moved by the same motor proteins, and motile node cilia (ventral) are needed to set up left/right asymmetry.
When is left-right asymmetry generally established order wise in comparison to other axes? When does asymmetry develop in the gut, heart, and lungs in the human embryo?
Last. Gut: 7 weeks, heart: 6 weeks, lungs: 5 weeks.
Is situs inversus always connected to Kartagener syndrome? What happens when single organ symmetry is inverted?
No. These people can be healthy. Single organ symmetry inversion can be fatal, usually when involving the heart, dextrocardia and levocardia.
How can left-right asymmetry be seen in the chick embryo with Nodal, Cerberus, and Pitx2
Pitx2 is a downstream TF of Nodal (it is activated by Nodal) and Cerberus, and all are mostly expressed on the left side of the embryo.
