Analysis of the cytoskeleton organization and its possible functions in male earthworm germ-line cysts equipped with a cytophore.

Karol Małota,Piotr Świątek

doi:10.1007/s00441-016-2398-6

Abstract

We studied the organization of F-actin and the microtubular cytoskeleton in male germ-line cysts in the seminal vesicles of the earthworm Dendrobaena veneta using light, fluorescent and electron microscopy along with both chemically fixed tissue and life cell imaging. Additionally, in order to follow the functioning of the cytoskeleton, we incubated the cysts in colchicine, nocodazole, cytochalasin D and latrunculin A. The male germ-line cells of D. veneta are interconnected via stable intercellular bridges (IB), and form syncytial cysts. Each germ cell has only one IB that connects it to the anuclear central cytoplasmic mass, the cytophore. During the studies, we analyzed the cytoskeleton in spermatogonial, spermatocytic and spermatid cysts. F-actin was detected in the cortical cytoplasm and forms distinct rings in the IBs. The arrangement of the microtubules changed dynamically during spermatogenesis. The microtubules are distributed evenly in whole spermatogonial and spermatocytic cysts; however, they primarily accumulate within the IBs in spermatogonia. In early spermatids, microtubules pass through the IBs and are present in whole cysts. During spermatid elongation, the microtubules form a manchette while they are absent in the cytophore and in the IBs. Use of cytoskeletal drugs did not alter the general morphology of the cysts. Detectable effects—the occurrence of nuclei in the late spermatids and manchette fragments in the cytophore—were observed only after incubation in nocodazole. Our results suggest that the microtubules are responsible for cytoplasmic/organelle transfer between the germ cells and the cytophore during spermatogenesis and for the positioning of the spermatid nuclei.Electronic supplementary materialThe online version of this article (doi:10.1007/s00441-016-2398-6) contains supplementary material, which is available to authorized users.

Highlights

Our results suggest that the microtubules are responsible for cytoplasmic/organelle transfer between the germ cells and the cytophore during spermatogenesis and for the positioning of the spermatid nuclei
We only describe the general aspects of spermatogenesis in D. veneta with the emphasis on the structure of the cysts and the cytoskeleton organization
The gem cells were clustered around the cytophore and, as a rule, each germ cell was connected to the cytophore by one intercellular bridges (IB) (Figs. 1, 2, 3, 4, 5)

Summary

Introduction

The formation of the syncytial groups of cells, which are usually called cysts, clusters, nests or isogenic groups, seems to be a conservative and widespread phase of animal gametogenesis (Pepling et al 1999; Ventelä 2006; Haglund et al 2011; Greenbaum et al 2011). It is widely accepted that the interconnections of germ cells into syncytial clusters regulate and synchronize germ cell development (Pepling et al 1999; Guo and Zheng 2004; Ventelä 2006; Greenbaum et al 2011; Haglund et al 2011; Amini et al 2014)

Methods

Results

Discussion

Conclusion