Body plan Flashcards
what follows fertilisation in Xenopus?
12 rapid cell divisions, 5 hours
Gastrulation follows mid-blastula transition and induction of mesoderm. Moving germ layers into final position.
What is the phylotypic stage?
Stage when the main properties of the phylum are appareant.
Describe cortical rotation?
Limited to Xenopus + few other teleosts
Uniformity is broken
The Sperm entry point dictates ventral side.
driven by array of microtubules and involved transport of dorsal determinants to prospective dorsal side
Cortex rotates 30degrees away from sperm entry site
What effect would UV treatment have upon a developing Xenopus embryo?
UV of vegetal pole results in ventralised embryos which lack dorso-anterior structures. Because UV disrupts microtubules + activation of Wnt pathway
Can tip embryo 90degrees to save this from happening.
What effect does LiCi have on Xenopus embryos?
Inhibitor of GSK3
Results in inhibition of GSK3 in embryos, hyper-activation of LiCl.
Activation of Wnt pathway everywhere within the early embryo - Dorsalised
What are the features of early mammalian embryos?
Regulative - ability to develop normally when parts are rearanged, or removed. Embryonic Stem Cells - pluripotent, can contribute to any cell type in body.
Even as late as gastrulation, any cell can contribute to either of 3 germ layers.
Early gastrulation stage embryo can tolerate loss of many cells.
Describe the role of Wnt in the mouse embryo
Required for gastrulation and mesoderm formation.
Extra Wnt activity results in posteriorisation
What is th Neiuwkoop centre?
Arises in early blastula and sets initial dorso-ventral polairty. The Spemanns Organizer then induced just above Nieuwkoop centre.
Neiuwkoop centre induces second axis when transplanted into opposite side of another embryo.
How does Wnt/B-catenin signalling act
interacts with VegT,
induces expression of Nodal Genes.
Several Nodal Genes in Xenopus, 1 in the mouse.
Nodal is a member of TGFB superfamily
NODAL SIGNALLING PRINCIPLE MESODERM INDUCER IN VERTEBRATES
What does the developent of dorso-anterior structures require?
Low BMP, Wnt and Nodal activities, organiser makes a cocktail of antagonists.
What happens to the organizer during gastrulation in Xenopus
Organizer becomes notochord and prechordal plate.
Describe Neurulation in Xenopus
1.Ectodermal overlying notochord become transformed into then neural plate.
2.Ectodermal cells either side of plate become thicken -FORMING NEURAL FOLDS
3.Neural folds converge neural plate to invaginate. Forming neural tube! precursor to CNS.
4. Neural crest cells form at junction between neural plate +neural folds
Neural crest cells contribute to formation of Nervous System.
BENDING OF NEURAL PLATE OCCURS AT MEDIAL HINGE POINT AND DORSOLATERAL HINGE POINT
Neurulation similar in most vertebrates
Phylotypic stage shortly after neurulation
Describe the two type of neural tube defects that result in failur of neural tube closure.
Spina bifida - failure closure at posterior
Anencephaly - failure of closure of anterior neural tube.
Causes poorly understood! - though folic acid known to protect against neural tube defects.
what is the evidence for the default model?
isolated ectodermal cells with BMP’s develop into epidermis, shows BNP inhibits neural development.
BMP’s can be eliminated from Xenopus by microinjecting antisense oligonucleotides into newly fertilised eggs. LOSS of BMP results in entire ectoderm being converted into neural plate cells
what are the skeptical problems with the Default Model?
Doubt whether it is SUFFICIENT
In chickens for example, both BMP and FGF signalling required for neural induction.
HOWEVER IT MAY BE APPLICABLE TO MAMMALS
