Morphological analysis of the human sperm tail during the early post-fertilization stage.

After fertilization, the human sperm tail lost its fibrous sheath at the pronuclear stage to become coiled and then attached to one of the first mitotic spindle poles. The tip of the sperm tail was branched and its degree did not change from the pronuclear stage to the second mitosis.

Acyl-CoA synthetase 6 regulates long-chain polyunsaturated fatty acid composition of membrane phospholipids in spermatids and supports normal spermatogenic processes in mice.

Long-chain polyunsaturated fatty acids (LCPUFAs), such as docosahexaenoic acid (DHA, 22:6) and docosapentaenoic acid (DPA, 22:5), have versatile physiologic functions. Studies have suggested that DHA and DPA are beneficial for maintaining sperm quality. However, their mechanisms of action are still unclear because of the poor understanding of DHA/DPA metabolism in the testis. DHA and DPA are mainly stored as LCPUFA-containing phospholipids and support normal spermatogenesis. Long-chain acyl-conenzyme A (CoA) synthetase (ACSL) 6 is an enzyme that preferentially converts LCPUFA into LCPUFA-CoA. Here, we report that ACSL6 knockout (KO) mice display severe male infertility due to attenuated sperm numbers and function. ACSL6 is highly expressed in differentiating spermatids, and ACSL6 KO mice have reduced LCPUFA-containing phospholipids in their spermatids. Delayed sperm release and apoptosis of differentiated spermatids were observed in these mice. The results of this study indicate that ACSL6 contributes to the local accumulation of DHA- and DPA-containing phospholipids in spermatids to support normal spermatogenesis.-Shishikura, K., Kuroha, S., Matsueda, S., Iseki, H., Matsui, T., Inoue, A., Arita, M. Acyl-CoA synthetase 6 regulates long-chain polyunsaturated fatty acid composition of membrane phospholipids in spermatids and supports normal spermatogenic processes in mice.

Melatonin is a potential drug for the prevention of bone loss during space flight.

Astronauts experience osteoporosis-like loss of bone mass because of microgravity conditions during space flight. To prevent bone loss, they need a riskless and antiresorptive drug. Melatonin is reported to suppress osteoclast function. However, no studies have examined the effects of melatonin on bone metabolism under microgravity conditions. We used goldfish scales as a bone model of coexisting osteoclasts and osteoblasts and demonstrated that mRNA expression level of acetylserotonin O-methyltransferase, an enzyme essential for melatonin synthesis, decreased significantly under microgravity. During space flight, microgravity stimulated osteoclastic activity and significantly increased gene expression for osteoclast differentiation and activation. Melatonin treatment significantly stimulated Calcitonin (an osteoclast-inhibiting hormone) mRNA expression and decreased the mRNA expression of receptor activator of nuclear factor κB ligand (a promoter of osteoclastogenesis), which coincided with suppressed gene expression levels for osteoclast functions. This is the first study to report the inhibitory effect of melatonin on osteoclastic activation by microgravity. We also observed a novel action pathway of melatonin on osteoclasts via an increase in CALCITONIN secretion. Melatonin could be the source of a potential novel drug to prevent bone loss during space flight.

Ultrastructural and histochemical evaluation of appositional mineralization of circumpulpal dentin at the crown- and root-analog portions of rat incisors.

Mineralization of circumpulpal dentin has been interpreted in such a way that predentin matrix is abruptly converted to almost fully mineralized dentin at the mineralization front. A group of investigators pointed out the existence of intermediary layer along the mineralization front of rat incisor dentin and claimed that dentin mineralization is a rather transient process. Owing to a paucity of information, however, the entity of transient mineralization of dentin has remained elusive. Here we confirmed the existence of a lightly mineralized layer (LL) along the mineralization front of rat incisor dentin, recognizable by both light and electron microscopy, in routinely processed specimens. LL less than 3 µm thick was shown to be located along the mineralization front of crown-analog dentin and tapered out toward the root analog of the incisor. Electron microscopy revealed that mineral deposition first occurred in the non-collagenous matrix of LL and that mineralization of collagen fibers took place sometime later at the conventional mineralization front. Microscopic appearance of the mineral phase of LL varied considerably depending on the histological processing of ultrathin sections, thus explaining the inconsistent interpretation of dentin mineralization in previous studies. These data suggest that mineralization of circumpulpal dentin in rat incisors proceeds in a stepwise or a transient manner, initiated by crystal deposition in the non-collagenous matrix followed by massive mineral deposition in collagen fibers at the mineralization front. The thickness of LL where only the non-collagenous matrix is mineralized may vary in relation to differences in the local non-collagenous matrix and also the rate of collagen mineralization in the respective portions of circumpulpal dentin.

Staphylococcus cohnii is a potentially biotherapeutic skin commensal alleviating skin inflammation.

Host-microbe interactions orchestrate skin homeostasis, the dysregulation of which has been implicated in chronic inflammatory conditions such as atopic dermatitis and psoriasis. Here, we show that Staphylococcus cohnii is a skin commensal capable of beneficially inhibiting skin inflammation. We find that Tmem79-/- mice spontaneously develop interleukin-17 (IL-17)-producing T-cell-driven skin inflammation. Comparative skin microbiome analysis reveals that the disease activity index is negatively associated with S. cohnii. Inoculation with S. cohnii strains isolated from either mouse or human skin microbiota significantly prevents and ameliorates dermatitis in Tmem79-/- mice without affecting pathobiont burden. S. cohnii colonization is accompanied by activation of host glucocorticoid-related pathways and induction of anti-inflammatory genes in the skin and is therefore effective at suppressing inflammation in diverse pathobiont-independent dermatitis models, including chemically induced, type 17, and type 2 immune-driven models. As such, S. cohnii strains have great potential as effective live biotherapeutics for skin inflammation.

Introduction of a three-dimensional and layered (TDL) culture, a novel primary co-culture method for ameloblasts and pulp-derived cells.

The enamel organ engaged in enamel matrix formation in tooth germs comprises four different cell types: the ameloblasts, the cells of the stratum intermedium, stellate reticulum, and the outer enamel epithelium, each characterized by distinct structural features. In ordinary primary cultures of tooth-derived cells, these cells generally become flat in profile and hardly regain their original profiles comparable to those in vivo, even under conditions that can induce the expression of functional markers from these cells. To overcome this limitation inherent to the cell culture of tooth-derived cells, we introduced a novel co-culture method, a "three-dimensional and layered (TDL) culture", a three-dimensional (3D) culture of dental pulp-derived cells dispersed in type I collagen gel combined with a layered culture of enamel epithelial cells seeded on top of the gel to establish thereby a culture condition where the functional tooth-derived cells regain their original structures and spatial arrangements. We subjected the TDL gels thus prepared to floating cultures and found that, in the layered epithelial cells, those facing the 3D gel became cuboidal/short columnar in shape, showed cell polarity and well-developed intercellular junctions, had PAS positive material in their cytoplasm, and expressed a distinct immunoreactivity for cyotokeratin 14 and amelogenins. Pulpal cells in the gel displayed a strong ALP activity throughout the 3D gel. The current observations have clearly shown that the structural and functional features reminiscent of early secretory ameloblasts could be restored in the enamel organ-derived cells in a TDL culture.

Development and terminal differentiation of pulp and periodontal nerve elements in subcutaneous transplants of molar tooth germs and incisors of the rat.

Ectopic tooth transplants are known to receive rich innervation of local neurons, but the precise location and structural features of neurites in the pulp and periodontal ligament (PDL) of such transplants are unclear. In this experiment, the molar tooth germs of rat embryos and incisors of young rats were subcutaneously transplanted into the dorsal regions of rats and processed, at various time intervals, for immunohistochemical demonstration of neural elements. Teeth with periodontal tissue elements developed in most of the molar transplants in 6 or 8 wk and received rich innervation, including some autonomic fibres, in the pulp. Nerve elements were also confirmed to be present in the PDL of these transplants, including specialized nerve ending-like structures reminiscent of the periodontal Ruffini endings. Mechanoreceptor-like structures were also induced in the regenerated PDL of similarly transplanted incisors, although the success rate was low. We conclude that rich and highly ordered innervation of the pulp, and occasional development of mechanoreceptors in the regenerated PDL of ectopic dental transplants, imply a high probability of successful induction of teeth with both nociceptive and mechanical sensations in the ectopic tooth and/or tooth germ transplant systems, although differentiation of mechanoreceptor-like nerve endings occurred in only a few rare cases.