scholarly journals Centroid, a novel putative DEAD-box RNA helicase maternal mRNA, is localized in the mitochondrial cloud in Xenopus laevis oocytes

2007 ◽  
Vol 51 (8) ◽  
pp. 701-706 ◽  
Author(s):  
Malgorzata Kloc ◽  
Agnes P. Chan
Keyword(s):  
Xenopus Laevis ◽  
Rna Helicase ◽  
Xenopus Laevis Oocytes ◽  
Maternal Mrna ◽  
Dead Box ◽  
Mitochondrial Cloud

Expression of XNOA 36 in the mitochondrial cloud of Xenopus laevis oocytes

Zygote ◽  
2011 ◽  
Vol 20 (3) ◽  
pp. 237-242 ◽  
Author(s):  
M.C. Vaccaro ◽  
M. Wilding ◽  
B. Dale ◽  
C. Campanella ◽  
R. Carotenuto
Keyword(s):  
Plasma Membrane ◽  
Xenopus Laevis ◽  
Stage I ◽  
Xenopus Laevis Oocytes ◽  
Cytoskeletal Network ◽  
Vegetal Cortex ◽  
Vegetal Pole ◽  
Mitochondrial Cloud ◽  
Germinal Plasm

SummaryIn Xenopus laevis oocytes a mitochondrial cloud (MC) is found between the nucleus and the plasma membrane at stages I–II of oogenesis. The MC contains RNAs that are transported to the future vegetal pole at stage II of oogenesis. In particular, germinal plasm mRNAs are found in the Message Transport Organiser (METRO) region, the MC region opposite to the nucleus. At stages II–III, a second pathway transports Vg1 and VegT mRNAs to the area where the MC content merges with the vegetal cortex. Microtubules become polarized at the sites of migration of Vg1 and VegT mRNAs through an unknown signalling mechanism. In early meiotic stages, the centrioles are almost completely lost with their remnants being dispersed into the cytoplasm and the MC, which may contain a MTOC to be used in the later localization pathway of the mRNAs. In mammals, XNOA 36 encodes a member of a highly conserved protein family and localises to the nucleolus or in the centromeres. In the Xenopus late stage I oocyte, XNOA 36 mRNA is transiently segregated in one half of the oocyte, anchored by a cytoskeletal network that contains spectrin. Here we found that XNOA 36 transcript also localises to the nucleoli and in the METRO region. XNOA 36 protein immunolocalization, using an antibody employed for the library immunoscreening that depicted XNOA 36 expression colonies, labels the migrating MC, the cytoplasm of stage I oocytes and in particular the vegetal cortex facing the MC. The possible role of XNOA 36 in mRNA anchoring to the vegetal cortex or in participating in early microtubule reorganization is discussed.

The structure of the mitochondrial cloud of Xenopus laevis oocytes

Development ◽  
1976 ◽  
Vol 36 (3) ◽  
pp. 697-710
Author(s):  
F. S. Billett ◽  
Elizabeth Adam
Keyword(s):  
Electron Microscopy ◽  
Electron Microscope ◽  
Xenopus Laevis ◽  
High Voltage ◽  
Xenopus Laevis Oocytes ◽  
Thin Sections ◽  
Balbiani Body ◽  
Mitochondrial Cloud ◽  
Microscopy Examination

The ultrastructure of the mitochondrial cloud (Balbiani body) of the pre-vitellogenic oocytes of Xenopus laevis has been examined using transmission and stereoscan electron microscopy. Examination of conventional thin sections confirm previous observations which suggest that the cloud consists essentially of many thousands of mitochondria and numerous small vesicles; larger clouds, in oocytes greater than 200µm in diameter, contain relatively more vesicles. Using a standard electron microscope at 100 kV very long and coursing arrays of mitochondrial profiles can be detected. The presence of very long mitochondrial lements has been confirmed using a high voltage microscope operating at 500–1000 kV. Stereoscan preparations, isolated from pre-vitellogenic oocytes, lend some support to the view that the mitochondrial cloud may consist of a mass of long filamentous mitochondria and the possibility that there are large continuous regions of mitochondrial material cannot be ruled out.

Mitochondrial number, cytochrome oxidase and succinic dehydrogenase activity in Xenopus laevis oocytes

Development ◽  
1981 ◽  
Vol 62 (1) ◽  
pp. 395-409
Author(s):  
E. Marinos ◽  
F. S. Billett
Keyword(s):  
Xenopus Laevis ◽  
Cytochrome Oxidase ◽  
Specific Activity ◽  
Succinic Dehydrogenase ◽  
Mitochondrial Fraction ◽  
Xenopus Laevis Oocytes ◽  
Mitochondrial Fractions ◽  
Rate Of Increase ◽  
Mitochondrial Cloud ◽  
Mitochondrial Number

An estimate has been made of the numbers of mitochondria in the mitochondrial cloud (Balbiani body) of Xenopus laevis oocytes ranging in size from 50 to 250 μm. The mitochondrial number is expressed in terms of a ‘standard ’ organelle measuring 2 μm in length and 0·2 μm in diameter and is derived by measurements on electron micrographs of sections through the cloud. It is found that the amount of mitochondrial material rises very rapidly as the oocyte grows in size. At the time the cloud disperses, in oocytes of about 300 μm in diameter, it is estimated that there are the equivalent of over 500000 mitochondria in each cell. The rate of increase is very similar to the rate of accumulation of mitochondrial DNA during the same period of growth. Using a polarographic technique the specific activity of cytochrome oxidase and succinic dehydrogenase was determined in mitochondrial fractions isolated from oocytes over a size range of 80–1200 μm in diameter. Although the specific activity of succinic dehydrogenase remains constant that of cytochrome oxidase falls sharply during the period when the mitochondria are replicating rapidly, i.e. up to about 300 μm diameter. In larger oocytes the specific activity of enzymes appears to remain constant but increasing contamination of the isolated mitochondrial fraction does not allow conclusions to be drawn from the enzyme loading of the mitochondria once they have dispersed from the cloud. The results are discussed in relation to the possibility that mitochondrial replication preceeds, or at least outpaces, mitochondrial differentiation during the course of oogenesis.

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