1. Introduction of the mesoderm and the organizer

mRNA localization

A-P patterning happens via _______ in Xenopus

ectoderm and endoderm

The asymmetric distribution of maternal determinants in the oocyte (animal and vegetal pole) allow for the eventual establishment of the ________________

mesoderm fate

the endoderm is capable of inducing the _______ on any ectoderm cells it comes in contact with

Maternal determinants in the oocyte

lead to animal vs. vegetal pole patterning

Animal pole

becomes the ectoderm

Vegetal pole

becomes the endoderm

Xnrs (Xenopus Nodal-related proteins)

mesoderm inducing signals highest on dorsal vegetal region

concentration dependent

Xnrs induce mesodermal fates in a ________ ______ manner

Mesoderm

Normal Endoderm: incubate the caps with vegetal masses and then separate produces a _______ cap

Ectoderm

Endoderm w/o Xnrs: incubate caps with vegetal masses and then separate produces a _______ cap

Nodal (Xnr) concentration and Vg1 presence

Mesoderm induction is dependent on 2 things

dorsal mesoderm (organizer)

the area where Xnrs are high and Vg1 is present

AP patterning

The localization of Vg1 and Xnr expression is a direct result of ________ which is a consequence of an asymmetric oocyte

BMP inhibitors

chordin and noggin

ventral fates

without chordin/noggin expression the cells will acquire ______ _____ by default

Belly

Low noggin expression produces a ____ piece

Back

High noggin expression produces a _____ piece

Cortical rotation, Disheveled and GBP, Beta-catenin, Xnrs, Xnrs + Vg1, Noggin

Organizer formation:

1. _______ _________

2. Movement of ______ and _______

3. ________ enters the nucleus

4. ____ (Nodal) are induced

5. _____ + _____ induce organizer genes

6. _____ is expressed

Functions of the organizer

1. Forms dorsal mesoderm structures

2. Dorsalizes adjacent mesoderm

3. Neural induction (dorsalizes ectoderm --> neural tube)

4. Initiates gastrulation movements

Organizer

"embryonic conductor" setting up dorsal identity and gastrulation

gastrulation movements

The organizer triggers _______ ______ leading to the germ layers adopting their eventual positions