Mouse oocytes within germ cell cysts and primordial follicles contain a Balbiani body - PubMed (original) (raw)

Mouse oocytes within germ cell cysts and primordial follicles contain a Balbiani body

Melissa E Pepling et al. Proc Natl Acad Sci U S A. 2007.

Abstract

The Balbiani body or mitochondrial cloud is a large distinctive organelle aggregate found in developing oocytes of many species, but its presence in the mouse has been controversial. Using confocal and electron microscopy, we report that a Balbiani body does arise in mouse neonatal germline cysts and oocytes of primordial follicles but disperses as follicles begin to grow. The mouse Balbiani body contains a core of Golgi elements surrounded by mitochondria and associated endoplasmic reticulum. Because of their stage specificity and perinuclear rather than spherical distribution, these clustered Balbiani body mitochondria may have been missed previously. The Balbiani body also contains Trailer hitch, a widely conserved member of a protein complex that associates with endoplasmic reticulum/Golgi-like vesicles and transports specific RNAs during Drosophila oogenesis. Our results provide evidence that mouse oocytes develop using molecular and developmental mechanisms widely conserved throughout the animal kingdom.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.

Fig. 1.

Electron micrographs of oocytes in neonatal ovaries. (A) Micrograph of an oocyte within a germline cyst from PND1 showing a well defined Balbiani body (arrow) with Golgi surrounded by mitochondria. (B) Micrograph of two oocytes from PND3 (top oocyte in a newly formed primordial follicle and bottom oocyte still within a germline cyst) with Balbiani bodies (arrows). (C) Micrograph of an oocyte within a primordial follicle at PND7 again showing a Balbiani body (arrow). (D) Higher-power view of Golgi from oocyte in C showing stacks of vesicles arranged in a circular structure. (E) Highly magnified image of mitochondria and associated ER with darkly stained potential nuage. (F) Oocyte with in primary follicle with mitochondria and ER evenly distributed throughout the cytoplasm. BB, Balbiani body; M, mitochondria; n, nucleus; Nu, nuage. (Scale bars: A_–_C, F, 5 μm; D, 1 μm; E, 0.5 μm.)

Fig. 2.

Fig. 2.

Balbiani body-associated Golgi vesicles in neonatal ovaries. (A_–_C) Confocal section of a PND1 oocyte labeled with a Golgi marker, GM130 (green) (A); Vasa, an oocyte marker (red) (B); and overlay (C) showing ring arrangement of Golgi (arrow). (D) Electron micrograph of Golgi at PND2 showing similar ring arrangement of Golgi (arrow). (Scale bar: 5 μm.)

Fig. 3.

Fig. 3.

Mitochondria in neonatal oocytes. (A_–_C) Confocal section of PND3 oocytes becoming assembled into primordial follicles labeled with an antibody against cytochrome c (green) to visualize mitochondria (A), Vasa (red) to visualize oocytes (B), and overlay (C) showing Balbiani body-associated mitochondria (arrow). (D_–_F) Confocal section of a PND4 oocyte within a growing primary follicle labeled with an antibody against cytochrome c (green) to visualize mitochondria (D), Vasa (red) to visualize oocyte (E), and overlay (F) showing mitochondria evenly distributed in the oocyte cytoplasm. (Scale bars: A_–_C, 5 μm; D_–_F, 10 μm.)

Fig. 4.

Fig. 4.

Conservation of the Balbiani body-associated protein, Tral. (A) Schematic representation of Drosophila and mouse Trailer hitch proteins showing the conserved Sm-like and FDF domains. (B) Comparison of amino acid sequence of the Sm-like domain from Drosophila and mouse. (C) Western blotting analysis using an antibody raised against Drosophila Trailer hitch. Mouse tissue extracts from 13.5 dpc, PND1, PND4, and PND42 ovaries and testes were probed with the Drosophila Tral antibody. An ≈60-kDa band was detected in all samples. Blots were reprobed with GAPDH (38 kDa) as a loading control. (D) Western blotting analysis of mouse tissue extracts from 9 dpc (F9), PND1 (P1), PND4 (P4), and adult (A) animals using an antibody raised against human RAP55. A band of ≈60 kDa was detected in all samples. Blots were reprobed with GAPDH (38 kDa) as a loading control. (E) Western blotting analysis of bacterially expressed RAP55. Extracts from bacteria with control pGEX4 plasmid (vector) or a plasmid expressing RAP55 were probed with Drosophila Trailer hitch antibody.

Fig. 5.

Fig. 5.

Expression of Tral protein in the Balbiani body of developing mouse ovaries and in adult testes. Immunofluorescence of single confocal ovary sections at 14.5 dpc (A) and at PND3 (B) labeled with an antibody against the Drosophila Tral protein (green) and propidium iodide (red) to visualize nuclei. (C) Immunofluorescence of a single confocal section showing coexpression of Trailer hitch protein (red) and Golgi marker GM130 (green) in developing ovaries at PND1. (D) Codetection of mouse Tral protein by antibodies generated against Drosophila Tral (red) and human RAP55 (green) in the mouse ovary at PND1. (E) Single confocal section through an adult mouse seminiferous tubule labeled with an antibody against the Drosophila Tral protein (green) and Vasa (red) showing that the Tral-rich body (arrows) is distinct from the chromatoid body (arrowheads). (Scale bars: A_–_C, E, 5 μm; D, 10 μm.)

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