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

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.

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

“…A future study of the mitochondrial networks and monitoring their dynamism in the cysts in the other stages of oogenesis could provide more comprehensive data. Linking the distribution of mitochondrial networks with their activity within the syncytial cysts, the polarized cells and common cytophore would also deliver interesting information, as was recently found in clitellate annelid male cysts [27,79] and female germ and somatic cells in the ovary of the earthworm Dendrobaena veneta [80]. In D. veneta ovary, not all of the mitochondria were active and the level of mitochondrial activity was di erent in the speci c types of germ cells (oogonia, NCs, oocytes) that were measured; however, it was always lower compared to the mitochondria activity in somatic ovarian cells [80].…”

Zespoły komórek płciowych w gametogenezie zwierząt - geneza, organizacja i funkcjonowanie

“…długiego cylindra -rachis u nicieni [64], lub mniej więcej sferycznej masy -cytofor u pierścienic (Ryc. 2E, 6E) [71][72][73][74], a sam kształt i wielkość cytoforu zazwyczaj zmieniają się w trakcie kolejnych etapów spermatogenezy. Liczba męskich komórek połączonych ze wspólną masą cytoplazmy może być różna, choć dane na ten temat są raczej fragmentaryczne.…”

“…Przykładowo, u wielu siodełkowców (dżdżownice) 128 spermatyd tworzy takie zespoły co oznacza siedem synchronicznych cykli podziałowych [21,75,76]. U pijawek znane są też przykłady zespołów zawierających 256, 512 lub 1024 spermatydy [72,77,78].…”