Germ layer formation and gastrulation Flashcards
Why is the oocyte polarised even before fertilisation?
Due to gravity some cytoplasmic factors are found exclusively in the vegetal hemisphere
What leads to blastocoel formation?
Changes in osmolarity- results in an influx of water
Where are Vg1+ expressing cells and Vg1- expressing cells found?
Vg1+ found below the blastocoel
Vg1- found above and by the sides of the blastocoel
What do Vg1 cells express?
VgT- a transcription factor
What does VgT bind to?
Promoter of the morphogen Nodal
Which levels of Nodal are found in which germ layer?
Highest level of nodal= Endoderm
Mid level of nodal= Mesoderm
No nodal= Ectoderm
What does the differing levels of Nodal explain?
- Why the vegetal hemisphere is so important- induces mesoderm and endoderm- otherwise the animal hemisphere would just be ectoderm
- How the germ layers form
What happens when sperm fertilises an egg?
A rotation of the cortex of the zygote occurs- by 30 degrees- dorsalising factors in the cortex moved to the dorsal side of the zygote
What produces the ‘Nieukwoop centre?’ And what does this overlap cause?
An overlap of nodal (TGF- beta) and beta catenin- in the dorsal region of the vegetal hemisphere
Overlap of these 2 regions causes ‘higher nodal activity’
Where is the Wnt signalling pathway activated?
The dorsal side of the embryo- marking the site where gastrulation will begin
What happens in regions of higher nodal activity and lower nodal activity?
Higher nodal activity- Organiser induced
Lower nodal activity- Ventral mesoderm induced
What T. factors do organiser cells express?
Goosecoid
Siamois
When is goosecoid expressed?
When both a beta catenin and TBF-beta downstream effector are bound
What do organiser cells differentiate into?
Axial mesoderm
Different levels of which genes cause the different types of axial mesoderm- notochord and prechordal mesoderm?
Siamois and goosecoid
