Yang C et al. (2022), Remnants of the Balbiani body are required for ...

XB-ART-59059

iScience 2022 Mar 18;253:103878. doi: 10.1016/j.isci.2022.103878.

Show Gene links Show Anatomy links

Remnants of the Balbiani body are required for formation of RNA transport granules in Xenopus oocytes.

Yang C , Dominique GM , Champion MM , Huber PW .

???displayArticle.abstract???
The Balbiani body (Bb), an organelle comprised of mitochondria, ER, and RNA, is found in the oocytes of most organisms. In Xenopus, the structure is initially positioned immediately adjacent to the nucleus, extends toward the vegetal pole, and eventually disperses, leaving behind a region highly enriched in mitochondria. This area is later transversed by RNP complexes that are being localized to the vegetal cortex. Inhibition of mitochondrial ATP synthesis prevents perinuclear formation of the transport complexes that can be reversed by a nonhydrolyzable ATP analog, indicating the nucleotide is acting as a hydrotrope. The protein composition, sensitivity to hexanediol, and coalescence in the absence of transport provide evidence that the transport RNP complexes are biocondensates. The breakdown of the Bb engenders regions of clustered mitochondria that are used not to meet extraordinary energy demands, but rather to promote a liquid-liquid phase separation.

???displayArticle.pubmedLink??? 35243240
???displayArticle.pmcLink??? PMC8861640
???displayArticle.link??? iScience
???displayArticle.grants??? [+]

???attribute.lit??? ???displayArticles.show???


	Figure 1. Expansion and dispersion of the Balbiani bodyOocytes at the designated stage of oogenesis were isolated from a transgenic frog that express GFP-tagged mitochondrial outer membrane protein 25. The Balbiani body forms in early stage I oocytes as a distinct structure on the germinal vesicle surface specifically facing the vegetal pole. During late stage I, the structure extends with the leading-edge delivering germ plasm to the vegetal cortex. During stage II, the Balbiani body fragments, resulting in a region enriched in mitochondria that persists into stage III.
	Figure 2. Remnants of the Balbiani body generate a region of elevated ATP that supports formation of RNA transport granulesGFP-tagged mitochondrial outer membrane protein 25 was used to monitor the position of mitochondria (mito); the FRET-based reporter protein ATeam was used to detect ATP (ATP); Alexa Fluor 546-labeled VLE RNA was used to track RNA localization (RNA)(A) The area formerly occupied by the Bb is enriched in mitochondria (left); VLE RNA being transported to the vegetal cortex (center) traverses the same area (right). The perinuclear cup structures where the RNA exits the vegetal side of the GV are enclosed in circles.(B) The clustered mitochondria of the Bb generate a region of elevated ATP concentration that is coincident with VLE RNA.(C–E). Inhibition of glycolysis (left panels) has no effect on localized ATP production (C), the clustering of mitochondria (D), or RNA transport (E). Inhibition of mitochondrial ATP synthesis with oligomycin (center panels) or antimycin (right panels) eliminates the clustered perinuclear region of ATP (C) and mitochondria (D), and suppresses formation of the RNA granules (E). Scale bars = 50 μm.
	Figure 3. Rescue of RNA granule formation with a nonhydrolyzable analog of ATPOocytes were injected with Alexa Fluor 546-labeled VLE RNA alone (top panels) or coinjection with adenosine 5'-(β,γ-imido) triphosphate (AMP-PNP) to give a calculated intracellular concentration of 4 mM (bottom panels). Oocytes were then cultured for 12 h in the absence (control) or presence of oligomycin (2 ug/mL) or antimycin (1.5 μg/mL).
	Figure 4. The VLE RNA transport granules behave as phase-separated biocondensate(A) Oocytes were taken 16 h after injection with Alexa Fluor 546-labeled VLE RNA and treated with 5% 1,6-hexanediol for 60 min and then fixed.(B) Depolymerization of microtubules with nocodazole. Oocytes were incubated with DMSO (vehicle control) or nocodazole (5 μg/mL) for 6 h, fixed and bisected prior to immunohistochemical staining using anti-β-tubulin/Alex Fluor 546-conjugated anti-rabbit antibodies.(C) Following injection with Alexa Fluor 546-labeled VLE RNA, oocytes were placed in culture medium containing DMSO or nocodazole for 48 h and then fixed. Scale bars = 50 μm unless noted otherwise.
	Figure 5. Protein-protein interaction map constructed from proteins identified in the VLE RNP complex affinity purified from oocyte extractGold background indicates proteins previously identified as binding directly to VLE RNA; blue background indicates newly identified proteins; VgRBP71 (khsrp), which binds directly to vg1 RNA was not identified in the MS samples.

References [+] :

Allison, Two distinct Staufen isoforms in Xenopus are vegetally localized during oogenesis. 2004, Pubmed, Xenbase