lecture 2 Flashcards
What happens at 3 and 8 weeks p.f?
3 weeks= formation of body axis
8 weeks= organogenesis- the formation of rudimentary organs via a huge signalling event
What cells are set aside early on in development?
adult stem cells to build the body or regenerate of an individual over its lifetime and gonadal stem cells to produce germ cells. They are separated early on from the somatic cells
What and how are primordial germ cells determined
They are developed on the outer edge of the embryo and migrate to the gonads. They need to be totipotent to give rise to an entire organism and need to be able to undergo meiosis to maintain diploid status for the next generation
Describe how a P-lineage cell arises in C. elegans
During early cleavage and gastrulation, asymmetric divisions produce a P-lineage cell due to the daughters acquiring different cytoplasmic components. The P cell remains in the very posterior of the embryo
Describe how P cells become germ cells?
1) they inherit P granules that bind to DNA and block transcription
2) they also block cytoplasmic translation as a fail safe device
3) they leave aprox 20 genes active to maintain stem cell fate and meiosis
How can P like cells in vertebrates be identified?
Use an antibody marker for NANOS (translation blocker) - cells stained at the posterior of the developing vertebrate are germ cells= pluripotent and can undergo meiosis
How to have widespread transcriptional inactivation
Via epigenetics- add methyl groups to DNA or modify histone tails to govern accessibility of gene promotors
What is the origin of PGCs
they arise from the mesodendodermal cells found in the posterior end of the embryo. They remain protected there until organogenesis (week 8 p.f.)- they migrate
How is the migration of drosophila P cells traced and what happens?
They express vasa which is used as a marker to trace them. They attach to gut endoderm and travel to the midgut and migrate out to the gonadal niche. A mix of chemoattractants and repellents drive this movement. Once they reach the niche they keep dividing until it is time to differentiate into either sperm or egg
What determines the environment for sperm/egg cells to differentiate?
Egg cells attach to the stromal cap and sperm attach to hub cells
describe PGC migration in vertebrates
They move from the extraembryonic territory to the hind/midgut boarder by following a trail of fibronectin using their integrin receptors. They then migrate out laterally into the genital ridges that secrete chemoattractants- they communicate with each other via reciprocal inductive interactions
How can you culture/induce egg and sperm?
Take fibroblasts and reprogram them to pluripotent state then culture them so they differentiate
What are support cells and what is their function?
They are cells that migrate and surround PGCs to secrete factors that insure that they maintain a stem cell phenotype
How do PGCs differentiate when in the wrong environment and what are the consequences?
Failure of migration out of the gut or failure to make stem cell factor causes the formation of teratomas meaning that fate alteration is coupled to axis formation and proper morphogenesis
