L2 - Germ cells Flashcards
what do germ cells give rise to
eggs and sperm
what is a stem cell niche
microenvironment which protects stem cells
when are the key organs developed
period of embryonic organogenesis - 3 weeks post fertilisation
when is the fatal period
week 8 onward
what is a gonadal germ stem cell
specialised totipotent cells set aside in the gonads
what does sexual reproduction require
the fusion of gametes to form the fertilised egg (zygote)
where to the primordial germ cells that give rise to the gametes arise
arise outside of the gonads and migrate into them
how are the primordial germ cells specialised
through a combination of cell non-autonomous signals, cell autonomous cytoplasmic determinants
outline w step process of germ cell determination
- primordial germ cells are determined in a specific location just on edge or outside of the developing embryo
- PGCs migrate to the gonad and become the progenitor population for eggs and sperm
what is needed for germ cell. determination
a plastic cell type (totipotent - zygote)
a cell capable of undergoing meiosis
what does division along the meridian line generate
2 identical daughter cells
what does division along the equator generate
2 different daughter cells
what do p cells inherit
P-granules (mix of proteins and RNAs) that are in cytoplasm but can get into nucleus
what do P-granules do
- bind to DNA of P-cell and block all transcription
- in cytoplasm they block translation
- promote stem cell fate, cause cells. to undergo meiosis rather than mitosis
where do P cell equivalents lie in vertebrates
Germ cells - lies at posterior part of developing embryo
what do Germ cells express
Nanos (transcriptional blocker)
mechanisms involved in wide spread shut down
epigenetic silencing mechanisms
- DNA methylation, represses gene activity
- Histone modification, histone proteins govern accessibility of gene promoters
what do primordial germ cells arise from
extra embryonic mesodendodermal cells just beyond the posterior part of the embryo
where are the PGCs determined
at the junction of the epiblast/hypoblast
what does position of where the PGCs are determined mean ?
that they are protected from the signals that are specifying the axes and controlling cell/tissue/organ differentiation
what type of divisions can PGCs undergo
meiotic NOT mitotic
when can PGCs go into the embryo
once rapid differentiation and early embryogenesis begins to decrease
what are PGCs in drosophila
pole cells
what to germ cells transcribe in drosophila
gene called Vasa
how can we follow pole cells
by following the expression of vasa
describe movement of the pole cells
attach to the endoderm and migrate through the midgut
after this they attach to the mesoderm
once they leave the midgut where do germ cells go
move sideways into future somites, where they are protected in the gonadal niche
where do PGCs cell attach in ovaries and testes
ovaries - stromal cap
testes - hub cells
outline genital ridges
provide specialised microenvironment that protects the PGCs in their pluripotent state, then supports their meiotic divisions and formation of either eggs or sperm cells
outline the travelling stem cell niche idea
supports cells travel with PGCs to maintain the stem cell phenotype
they secrete stem cell factor (SCF)
what happens if primordial germ cells fail to migrate out of the gut . fail to be protected in the gonads
teratoma is produced
