Vertebrate Development Maternal to Zygotic Control (Advances in Experimental Medicine and Biology)

Buckyball

Animal mRNAs: cyclin B1, pou5f3 (pou2) and Vg1 (in zebrafish)Oocyte maturation

++-+

Meiosis I (diplotene) Meiosis II (Metaphase)

Stage II 140-340

Micropyle

A

V

Stage III 340-690 Stage IV 690-730

Bb

Vg 1

Vg 1 Vg^1

brul brul

mago nashi brul

mago nashi

vasa

Bb formation

Bb disassembly

cortical granules

Nuclear migration

+++++

• 
  


• ++ - -

• 
  
  
  
  • 
    
  
  
  
  

+

---

Zygotene bouquet

Symmetry

breaking

Radially symmetric

First polarized

localization

Mitosis

Bb precursors components

(Buc, GasZ, mitochondria)

Meiosis I (prophase)

Bb precursors components

(Buc,dazl, mitochondria)

Bb localized proteins:Buckyball, Rbpms2 and GasZ

Oogonia

Pachytene-diplotene

Bb

Vg 1

Vg 1

brul brul

mago nashi brul

mago nashi

Vg 1

A

V

Vg 1

Vg 1 Vg^1

brul brul

mago nashi brul

mago nashi

Macf1

Acetylated

microtubules

centrosome

telomeres

Kinesin

Vegetal mRNAs (Early pathway): dazl, nanos, grip2a and syntabulin ; wnt8 (in zebrafish)

Vegetal mRNAs (Late pathway): mago nashi and bruno-like (in zebrafish); wnt1 1 , Vg1 and VegT (in frog)

A

B

C

Nucleolus

Vg 1

Vg 1 Vg^1

mago nashi

nanos mago nashi

nanos

brul

brul

brul

Polar body extrusion

Fig. 5.2 RNA localization and AV axis establishment during oogenesis. (a) In premeiotic oogonia,
Bb precursors are distributed radially in the cytoplasm, telomeres are scattered intranuclearly, and the
centrosome (yellow) is at a perinuclear position, possibly positioned facing the cytoplasmic bridge of
the last mitotic division. When meiosis initiates, specifically during zygotene stages, Bb precursors
(red) localize around the centrosome and adjacent to the telomere cluster (cyan) of the zygotene
bouquet configuration. Thus, the nuclear axis of the bouquet configuration predicts the AV axis of the
oocyte. At this stage, acetylated tubulin cables (dark green) form and may connect sister oocyte pairs
through the cytoplasmic bridges of the last mitotic oogonial division (a pair is shown). (b) At the
subsequent pachytene stage, a nuclear cleft forms at the centrosome position where Bb precursors
aggregate. The nuclear cleft remains throughout pachytene and early diplotene. In mid-diplotene, the
nuclear envelope rounds out and the mature spherical Bb forms marking the position of the prospec-
tive vegetal pole of the oocyte. The formation of the Bb and its disassembly requires Bucky ball and
Macf1 function, respectively. Hence, Bucky ball and Macf1 regulate RNA localization to the vegetal
pole through the early pathway and are also required for AV polarity establishment. (c) At stage II,
Bb RNAs are localized to the vegetal pole (red). Distinct RNAs localize to the animal pole (light
blue) and cortical granules (white ovoid) are formed. vasa RNA is broadly localized at the vegetal
pole (pink) and expands radially cortically at subsequent stages. At stage III, previously unlocalized
RNAs (yellow) are transported to the vegetal pole on microtubules tracks (brown) by the action of

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