Tourmente S, Lecher P, Degroote F, Renaud M
Laboratoire de Biochimie Médicale, Faculté de Médecine, Université Clermont I, Clermont-Ferrand, France.
Biol Cell. 1990;68(2):119-27. doi: 10.1016/0248-4900(90)90296-f.
The changes in distribution and density of mitochondria and the level of mitochondrial RNA during Drosophila oogenesis were studied simultaneously in the 3 cell types ie follicle cells, nurse cells and oocyte, making up the egg chamber. Up to stage 6, mitochondrial density (mitochondrial and cellular areas ratio) was elevated and increased similarly in both follicle and nurse cells. Thereafter the mitochondrial density of follicle cells continued to increase and that of the nurse cells declined markedly while the nurse cell mitochondria assembled in dense groups and decreased in size. This can be related to a transfer of nurse cell cytoplasm, including mitochondria, to the oocyte. In the oocyte from stage 4 to stage 7 we observed a significant decrease of the mitochondrial density due to the absence of mitochondrial biogenesis. Then the cytoplasm transfer caused mitochondrial density to increase up to the level found in the nurse cells at the end of oogenesis. The mature oocyte contains enough mitochondria to supply 15,000 somatic cells. Our results strongly suggest that the variations in size, distribution and density of mitochondria relate to the particular energetic requirements of the different cell types during the first half of oogenesis. Later they relate to the developmental requirements of the nurse cells and the oocyte, in particular the storage of mitochondria in the oocyte. The level of mitochondrial RNA was studied through in situ hybridization. Throughout oogenesis the follicle and nurse cell RNA evolved similarly. Up to stage 9, there was no change in RNA densities in these cells, suggesting a correlation with the cell volume and/or the nuclear DNA content. Thereafter the cellular RNA concentration declined rapidly. In the oocyte the RNA concentration evolved differently especially from stage 10 to the end, the RNA density being stabilized. This can be related to the injection of nurse cell mitochondria, followed by their assignment to reserve status. Our results suggest that the mt RNA density is under extramitochondrial control mechanisms.
在果蝇卵子发生过程中，对构成卵室的三种细胞类型，即卵泡细胞、滋养细胞和卵母细胞中线粒体的分布、密度变化以及线粒体RNA水平进行了同步研究。直至第6阶段，卵泡细胞和滋养细胞中的线粒体密度（线粒体与细胞面积之比）均升高且升高幅度相似。此后，卵泡细胞的线粒体密度持续增加，而滋养细胞的线粒体密度显著下降，同时滋养细胞线粒体聚集成密集团块且体积减小。这可能与包括线粒体在内的滋养细胞细胞质向卵母细胞的转移有关。在第4阶段至第7阶段的卵母细胞中，由于线粒体生物发生缺失，我们观察到线粒体密度显著降低。随后的细胞质转移使线粒体密度增加至卵子发生末期滋养细胞中的水平。成熟卵母细胞含有足够的线粒体以供应15,000个体细胞。我们的结果有力地表明，线粒体大小、分布和密度的变化与卵子发生前半段不同细胞类型的特定能量需求有关。后期它们与滋养细胞和卵母细胞的发育需求有关，特别是卵母细胞中线粒体的储存。通过原位杂交研究了线粒体RNA水平。在整个卵子发生过程中，卵泡细胞和滋养细胞的RNA变化相似。直至第9阶段，这些细胞中的RNA密度没有变化，表明与细胞体积和/或核DNA含量相关。此后细胞RNA浓度迅速下降。在卵母细胞中，RNA浓度变化不同，尤其是从第10阶段到末期，RNA密度稳定。这可能与注入滋养细胞线粒体并随后将其转变为储备状态有关。我们的结果表明线粒体RNA密度受线粒体外控制机制调控。
