homework 2 Flashcards
what is the most important characteristic of germ cells?
Just like the neural crest cells, the germ cells’ most important characteristic is that they migrate towards their final location, which is the future gonads
Their movement is realised by them recognizing specific repellants and chemoattractants that help them migrate, but also what they need is an internal reprogramme that rearranges their cytoskeleton.
One of these attractants is Hmgcr.
why are germ cells separated from the rest of the body in the early development?
In order to avoid somatic signalling that happens in the somatic compartment of the embryo. Germ cells need to maintain their own programme, they do not need any zygotic activation of genes. They just carry parental infromation and therefore less mutations are likely to occur.
They separate so early in order to avoid the ‘’feeling’’ of the transcriptional programmes that happen in the rest of the body, so they do not get confused by somatic cell divisions happening in the body.
what are the 2 mechanisms (in mammals) for generation of germ cells?
Preformation and Epigenesis
Preformation = determined by germplasm components
Epigenesis = induction through cell-to-cel signaling
what would happen if all sister chromatid cohesion is lost at metaphase to anaphase transition of the first meiotic division?
So MI would still proceed normally since microtubules are aldready pulling in the correct direction, before cohesion is removed, but there will be random segregation in the second round of meiosis.
what is the receptor on the surface of ovulated eggs that interacts with the acrosome of sperm?
it is called juno and it is essential for fertilization. It may contribute to the membrane block to polyspermy. Following fertilization, it is rapidly shed from the egg membrane and redistributed as vesicles, which may bind and rapidly neutralize subsequent incoming acrosome-reacted sperm, thereby reducing the possibility of creating nonviable polyploid embryos.
what happens if dorsal is cytoplasmic?
the entire embryo becomes dorsalized
if dorsal is nuclear, entire embryo becomes ventralised.
what happens at the molecular level during cortical rotation?
The cytoskeleton is reorganised and RNA molecules are sent to the opposite side of the sperm entry point. This defines the DV axis in Xenopus.
But not in mammals, DV axis in mammals is defined much later in development
