Morphology of Mitochondria in Syncytial Annelid Female Germ-Line Cyst Visualized by Serial Block-Face SEM.

Anna Z Urbisz,Karol Małota,Sebastian Student,Małgorzata A Śliwińska

doi:10.1155/2020/7483467

Abstract

Mitochondria change their morphology and distribution depending on the metabolism and functional state of a cell. Here, we analyzed the mitochondria and selected structures in female germ-line cysts in a representative of clitellate annelids – the white worm Enchytraeus albidus in which each germ cell has one cytoplasmic bridge that connects it to a common cytoplasmic mass. Using serial block-face scanning electron microscopy (SBEM), we prepared three-dimensional ultrastructural reconstructions of the entire selected compartments of a cyst at the advanced stage of oogenesis, i.e. the nurse cell, cytophore, and cytoplasmic bridges of all 16 cells (15 nurse cells and oocyte). We revealed extensive mitochondrial networks in the nurse cells, cytophore and mitochondria that pass through the cytoplasmic bridges, which indicates that a mitochondrial network can extend throughout the entire cyst. The dynamic hyperfusion state was suggested for such mitochondrial aggregations. We measured the mitochondria distribution and revealed their polarized distribution in the nurse cells and more abundant accumulation within the cytophore compared to the nurse cell. A close association of mitochondrial networks with dispersed nuage material, which seems to be the structural equivalent of a Balbiani body, not described in clitellate annelids so far, was also revealed.

Highlights

Mitochondria are highly dynamic organelles that are primarily specialized in producing energy by generating most of the adenosine triphosphates (ATP)
The morphology of mitochondria, their spatial distribution and activity are changeable in cells depending on their temporary requirements. e dynamism of mitochondria is the result of two opposing processes: fusion, which leads to their merging into larger mitochondrial networks and ssion, which is the process of separation of an individual mitochondrion from the network. e morphology of mitochondria depends on the balance between these processes [3, 6,7,8,9,10,11,12,13,14,15,16]
The oocyte continues meiosis, grows considerably and becomes the egg cell, while the nurse cells (NC) function as supporting cells and deliver at least cell organelles to the oocyte [52, 69]. e architecture of the cysts is always the same – the germ cells are located at the cyst periphery and they are connected to a common mass of cytoplasm that is located in the center of the cyst. e cytophore is a small, roughly spherical cytoplasmic mass that is devoid of nuclei and each germ cell is connected to it by one ring canal (RC) (Figures 1(a), 1(c), 2(a), and 4(a))

Summary

Introduction

Mitochondria are highly dynamic organelles that are primarily specialized in producing energy by generating most of the adenosine triphosphates (ATP). To maintain cells in proper energetic metabolism and homeostasis, they play other important roles in intermediary metabolism, calcium signaling and apoptosis [1,2,3,4,5]. In this context, the morphology of mitochondria, their spatial distribution and activity are changeable in cells depending on their temporary requirements. E dynamism of mitochondria is the result of two opposing processes: fusion, which leads to their merging into larger mitochondrial networks and ssion, which is the process of separation of an individual mitochondrion from the network. Mitochondrial networks have been found in di erent types of cells. eir genetic basis and the molecular mechanisms of how they fuse into larger systems or split into single organelles have been intensively studied in model organisms such as yeast and mammalian tissue cell cultures [18,19,20,21,22]

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