ARF6, a component of intercellular bridges, is essential for spermatogenesis in mice

Male germ cells are connected by intercellular bridges (ICBs) in a syncytium due to incomplete cytokinesis. Syncytium is thought to be important for synchronized germ cell development by interchange of cytoplasmic factors via ICBs. Mammalian ADP-ribosylation factor 6 (ARF6) is a small GTPase that is involved in many cellular mechanisms including but not limited to regulating cellular structure, motility, vesicle trafficking and cytokinesis. ARF6 localizes to ICBs in spermatogonia and spermatocytes in mice. Here we report that mice with global depletion of ARF6 in adulthood using Ubc-CreERT2 display no observable phenotypes but are male sterile. ARF6-deficient males display a progressive loss of germ cells, including LIN28A-expressing spermatogonia, and ultimately develop Sertoli-cell-only syndrome. Specifically, intercellular bridges are lost in ARF6-deficient testis. Furthermore, germ cell-specific inactivation using the Ddx4-CreERT2 results in the same testicular morphological phenotype, showing the germ cell-intrinsic requirement of ARF6. Therefore, ARF6 is essential for spermatogenesis in mice and this function is conserved from Drosophila to mammals.

Ovary micromorphology in hormogastrid earthworms with a particular emphasis on the organization of the germline cysts

There is a gap in our knowledge of microorganization and the functioning of ovaries in earthworms (Crassiclitellata) and allied taxa. Recent analyses of ovaries in microdriles and leech-like taxa revealed that they are composed of syncytial germline cysts accompanied by somatic cells. Although the pattern of cyst organization is conserved across Clitellata - each cell is connected via one intercellular bridge (ring canal) to the central and anuclear cytoplasmic mass termed the cytophore - this system shows high evolutionary plasticity. In Crassiclitellata, only the gross morphology of ovaries and their segmental localization is well known, whereas ultrastructural data are limited to lumbricids like Dendrobaena veneta. Here we present the first report about ovarian histology and ultrastructure in Hormogastridae, a small family of earthworms inhabiting the western parts of the Mediterranean sea basin. We analyzed three species from three different genera and showed that the pattern of ovary organization is the same within this taxon. Ovaries are cone-like, with a broad part connected to the septum and a narrow distal end forming an egg string. Ovaries are composed of numerous cysts uniting a small number of cells, eight in Carpetania matritensis. There is a gradient of cysts development along the long ovary axis, and three zones can be distinguished. In zone I, cysts develop in complete synchrony and unite oogonia and early meiotic cells (till diplotene). Then (zone II), the synchrony is lost, and one cell (prospective oocyte) grows faster than the rest (prospective nurse cells). In zone III, oocytes pass the growth phase and gather nutrients; at this time, their contact with the cytophore is lost. Nurse cells grow slightly, eventually die via apoptosis, and are removed by coelomocytes. The most characteristic feature of hormogastrid germ cysts is the inconspicuous cytophore in the form of thread-like thin cytoplasmic strands (reticular cytophore). We found that the ovary organization in studied hormogastrids is very similar to that described for D. veneta and propose the term "Dendrobaena" type of ovaries. We expect the same microorganization of ovaries will be found in other hormogastrids and lumbricids.

Expression analysis of genes encoding TEX11, TEX12, TEX14 and TEX15 in testis tissues of men with non-obstructive azoospermia

Objective

Spermatogenesis is a complex process controlled by a plethora of genes. Changes in expression and function of these genes may thus lead to spermatogenic deficiency and male infertility. TEX11, TEX12, TEX14 and TEX15 are germ cell-specific genes expressed in the testis. TEX11, involved in the initiation and maintenance of chromosome synapses in meiotic chromosomes, has been shown to be essential for meiosis and fertility in males. TEX14, a component of intercellular bridges in germ cells, is required for spermatogenesis and fertility. TEX12 and TEX15 are essential for correct assembly of the synaptonemal complex and thus meiosis progression.

Methods

In order to examine whether changes in expression of these genes is associated with impaired spermatogenesis, expression levels of these genes were quantified by RT-qPCR on samples retrieved from infertile patients submitted to diagnostic testicular biopsy at Royan institute. Samples were divided into two groups of 18 patients with non-obstructive azoospermia considered as case; nine patients with obstructive azoospermia were included in the control group.

Results

A significant down-regulation of these genes was observed in the SCOS group when compared to the control group.

Conclusion

This result suggests that regular expression of TEX11, TEX12, TEX14 and TEX15 is essential for the early stages of spermatogenesis.

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

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.

Intercellular bridges are essential for human parthenogenetic cell survival

Parthenogenetic cells, obtained from in vitro activated mammalian oocytes, display multipolar spindles, chromosome malsegregation and a high incidence of aneuploidy, probably due to the lack of paternal contribution. Despite this, parthenogenetic cells do not show high rates of apoptosis and are able to proliferate in a way comparable to their biparental counterpart. We hypothesize that a series of adaptive mechanisms are present in parthenogenetic cells, allowing a continuous proliferation and ordinate cell differentiation both in vitro and in vivo. Here we identify the presence of intercellular bridges that contribute to the establishment of a wide communication network among human parthenogenetic cells, providing a mutual exchange of missing products. Silencing of two molecules essential for intercellular bridge formation and maintenance demonstrates the key function played by these cytoplasmic passageways that ensure normal cell functions and survival, alleviating the unbalance in cellular component composition.

Gonads and gametogenesis in astigmatic mites (Acariformes: Astigmata)

Astigmatans are a large group of mites living in nearly every environment and exhibiting very diverse reproductive strategies. In spite of an uniform anatomical organization of their reproductive systems, gametogenesis in each sex is highly variable, leading to gamete formation showing many peculiar features and emphasizing the distinct position of Astigmata. This review summarizes the contemporary knowledge on the structure of ovaries and testes in astigmatic mites, the peculiarities of oogenesis and spermatogenesis, as well as provides new data on several species not studied previously. New questions are discussed and approaches for future studies are proposed.

Gonads in Histiostoma mites (Acariformes: Astigmata): structure and development

The development of male and female gonads in arrhenotokous and thelytokous species of Histiostoma was studied using transmission electron microscopy (TEM). All instars were examined: larvae, protonymphs, facultative heteromorphic deutonymphs (=hypopi), tritonymphs, and adults. In testis primordium, spermatogonia surrounding a testicular central cell (TCC) with a gradually enlarging, branched nucleus are present already at the larval stage. Spermatogonia and the TCC are connected via narrow, tubular intercellular bridges revealing that the TCC is a germline cell. Spermatocytes appear at the protonymphal stage. At the heteromorphic deutonymph stage, the testis primordium is similar to that of the protonymph, but in the tritonymph it is much larger and composed as in the adult: spermatids as well as sperm cells are present. The latter are congregated ventrally in the testis at the entrance of the deferent duct. In the larval ovary, an eccentrically located ovarian nutritive cell (ONC) is surrounded by oogonia which are connected with the ONC via tubular intercellular bridges. In later stages, the ovary grows and oocytes appear in the protonymph. Meiotic synaptonemal complexes in oocytes occur from the tritonymph stage. At about the time of the final molting, tubular intercellular bridges transform into peculiar diaphragm-crossed bridges known only in Histiostoma mites. In the adult female, growing oocytes at the end of previtellogenesis lose intercellular bridges and move ventro-laterally to the ovarian periphery towards the oviduct entrance. Vitellogenesis occurs in oviducts. Germinal cells in both the testis and ovary are embedded in a few somatic stroma cells which may be well discernible already in the larval ovary; in the testis, somatic stroma cells are evident not earlier than the end of the tritonymphal stage. The ovary has a thin wall of flat somatic cells, whereas the testis is covered by a basal lamina only. The obtained results suggest that gonads in Histiostoma and other Astigmata originate from two primordial cells only.