Abundant Actin Filaments Research Articles

Telocytes: novel interstitial cells present in the testis parenchyma of the Chinese soft-shelled turtle Pelodiscus sinensis.

Telocytes (TCs) are novel interstitial cells that have been found in various organs, but the existence of TCs in the testes has not yet been reported. The present ultrastructural and immunohistochemical study revealed the existence of TCs and differentiate these cells from the peritubular cells (Pc) in contact with the surrounding structures in the testes. Firstly, our results confirmed the existence of two cell types surrounding seminiferous tubules; these were Pc (smooth muscle like characteristics) and TCs (as an outer layer around Pc). Telocytes and their long thin prolongations called telopodes (Tps) were detected as alternations of thin segments (podomers) and thick bead-like portions (podoms), the latter of which accommodate the mitochondria and vesicles. The spindle and irregularly shaped cell bodies were observed with small amounts of cytoplasm around them. In contrast, the processes of Pc contained abundant actin filaments with focal densities, irregular spine-like outgrowths and nuclei that exhibited irregularities similar to those of smooth muscle cells. The TCs connected with each other via homocellular and heterocellular junctions with Pc, Leydig cells and blood vessels. The Tps of the vascular TCs had bands and shed more vesicles than the other TCs. Immunohistochemistry (CD34) revealed strong positive expression within the TC cell bodies and Tps. Our data confirmed the existence and the contact of TCs with their surroundings in the testes of the Chinese soft-shelled turtle Pelodiscus sinensis, which may offer new insights for understanding the function of the testes and preventing and treating testicular disorders.

Abundance of actin filaments in the preprophase band and mitotic spindle of brick1 Zea mays mutant

The preprophase band and mitotic spindle of dividing protodermal cells of wild-type Zea mays leaves include few actin filaments. Surprisingly, abundant actin filaments were observed in the above arrays, in dividing protodermal cells in the leaves of the brick1 mutant. The same abundance was observed in the spindle of Taxol-treated brick1 mitotic protodermal cells. Apart from the above difference, the relevant arrays displayed normal microtubule organization in both wild type and mutant cells, as far as can be discerned by immunofluorescence microscopy. Accordingly, the abundance of actin filaments in the preprophase band and spindle of brick1 mitotic cells seems not to influence the structure of the above arrays and might be a non-functional "side-effect" of defective F-actin organization in this mutant.

Reversible protein phosphorylation regulates the dynamic organization of the pollen tube cytoskeleton: effects of calyculin A and okadaic acid.

We investigated the cytoskeleton of Lilium longiflorum pollen tubes and examined the effects of the type 2A protein phosphatase (PP2A) inhibitors calyculin A and okadaic acid. An improved method for actin visualization, the simultaneous fixation and staining with rhodamine-labelled phalloidin during microscopical observation, revealed abundant actin filaments of no preferential orientation in the apical clear zone. Microtubules, visualized by indirect immunofluorescence, were mostly absent from the apices of straight-growing pollen tubes but present in those with irregular shape. Double labelling showed that both actin bundles and microtubules had a similar longitudinal or slightly helical orientation in the pollen tube shaft. In the presence of 30 nM calyculin A or okadaic acid, pollen tubes grew very slowly, branched frequently, and contained isolated, randomly oriented, curved actin bundles and microtubules. Treating pollen tubes with calyculin A or okadaic acid after germination arrested growth immediately, reversibly altered the alignment of actin bundles from axial to transverse, and disassembled microtubules. The changes in actin organization caused by the PP2A inhibitors were similar to those observed upon overexpression of AtRop1 (Y. Fu, G. Wu, Z. Yang, Journal of Cell Biology 152: 1019-1032, 2001), suggesting that hyperphosphorylation interferes with the signalling pathway of small GTPases. The effects of the PP2A inhibitors could be ameliorated with nanomolar concentrations of latrunculin B.

Ectoderm exerts the driving force for gastrulation in the sand dollar Scaphechinus mirabilis.

How the ectodermal layer relates to the invagination processes was examined in the sand dollar Scaphechinus mirabilis. When the turgor pressure of blastocoele was increased, invagination was completely blocked. In contrast, an increase in turgor pressure did not affect elongation of the gut rudiment in the regular echinoid Hemicentrotus pulcherrimus. Rhodamine-phalloidin staining showed that the distribution of actin filaments was different between two species of embryos. In S. mirabilis gastrulating embryos, abundant actin filaments were seen at the basal cortex of ectoderm in addition to archenteron cells, while the intense signal was restricted to the archenteron in H. pulcherrimus. To investigate whether actin filaments contained in the ectodermal layer exert the force of invagination, a small part of the ectodermal layer was aspirated with a micropipette. If S. mirabilis embryos were aspirated from the onset of gastrulation, invagination did not occur at all, irrespective of the suction site. Even after the archenteron had invaginated to one-half of its full length, further elongation of the archenteron was severely blocked by suction of the lateral ectoderm. In contrast, suction of the ectodermal layer did not affect the elongation processes in H. pulcherrimus. These results strongly suggest that the ectodermal layer, especially in the vegetal half, exerts the driving force of invagination in S. mirabilis.

Peritubular myoid cells in the testis: their structure and function.

Peritubular myoid cells, surrounding the seminiferous tubules in the testis, have been found in all mammalian species, but their organization in the peritubular interstitial tissue varies by species. In laboratory rodents, including rats, hamsters and mice, only one layer of myoid cells is seen in the testis. The cells in these animals are joined by junctional complexes as are epithelial cells. On the other hand, several cellular layers exist in the lamina propria of the seminiferous tubule in the human and some other animals. Myoid cells contain abundant actin filaments which are distributed in the cells in a species-specific manner. In the rat, the filaments within one myoid cell run both longitudinally and circularly to the long axis of the seminiferous tubule, exhibiting a lattice-work pattern. The arrangement of the actin filaments in the cells changes during postnatal development, and the disruption of spermatogenesis, such as cryptorchidism, seems to affect further the arrangement of the filaments. Other cytoskeletal proteins, including myosin, desmin/vimentin and alpha-actinin, are also found in the cells. Myoid cells have been shown to be contractile, involved in the transport of spermatozoa and testicular fluid in the tubule. Several substances (prostaglandins, oxytocin, TGF beta, NO/cGMP) have been suggested to affect the contraction of the cell, though the mechanisms of the contraction are still unknown. Recent in vitro studies have demonstrated that the cells secrete a number of substances including extracellular matrix components (fibronectin, type I and IV collagens, proteoglycans) and growth factors (PModS, TGF beta, IGF-I, activin-A). Some of these substances are known to affect the Sertoli cell function. Furthermore, it has been reported that myoid cells contain androgen receptors and are involved in retinol processing. Considering all this, it is evident that peritubular myoid cells not only provide structural integrity to the tubule but also take part in the regulation of spermatogenesis and the testicular function. Their precise roles, however, remain to be solved.

Changes in the arrangement of actin filaments in myoid cells and Sertoli cells of rat testes during postnatal development and after experimental cryptorchidism.

Abundant actin filaments are present in myoid cells and Sertoli cells in the testis. In the adult rat, the filaments form a lattice arrangement within the myoid cell, and show a hexagonal pattern in the basal junctional regions of Sertoli cells. Isolated seminiferous tubules and frozen sections were prepared from juvenile to adult Wistar rat testes, stained with FITC-conjugated phalloidin, and observed by confocal microscopy. Unilateral cryptorchidism was induced in adult rats, and seven days later, their testes were also examined. In the myoid cell, parallel actin filaments running circularly around the seminiferous tubules were observed at 15 and 20 days of age. Then, at 30 days, actin filaments arranged longitudinally along the tubular long axis appeared in addition to the circular bundles. A lattice arrangement of actin-filament bundles in myoid cells became obvious at 40 days, when elongated spermatids are found in the tubule. Actin filaments in the basal junctional regions of Sertoli cells did not acquire the hexagonal pattern seen in the adult testis until 30 days of age. In the cryptorchid testes, the arrangement of actin filaments in the both cells showed a remarkable change compared to the control testis; the filaments became thinner and disrupted. A lattice arrangement of the actin filaments in the myoid cell appear at around 30 days, before the completion of spermatogenesis. A hexagonal pattern of the filaments in the junctional regions of Sertoli cells has already developed at this age. Cryptorchidism affects the actin filaments of the both cells.

The spatial distribution of spindle microtubules in anaphase 3Y1 cells

The spatial distribution of the microtubules (MT) in the rat 3Y1 cells in mitosis was investigated by immunoelectron microscopy and computer-graphic reconstruction of serial thin sections. In anaphase the interzone-MT increased in number gradually with advancing phase, while the kinetochore-MT in half-spindles decreased. The interzone-MT overlapped with each other at the equatorial region of the cell, and they formed a specific structure called the 'stem bodies'. The ends of the interzone-MT opposite to the stem bodies often attached to chromosomes but not to the poles. The stem bodies were not labeled with immunogold particles of anti-alpha tubulin. Some of the stem bodies or MT which originate from stem bodies were found just beneath the plasma membrane in the equatorial region where abundant actin filaments appear showing the formation of the contractile ring and subsequently the cleavage furrow begins. On the basis of these observations it is assumed that the interzone-MT is involved both in the separation of chromosomes in anaphase and in the formation of the cleavage furrow in telophase.

Structural relationships between the endothelial actin system and the underlying elastic layer in the distal interlobular artery of the rat kidney.

The structure of the intracellular actin filaments and the extracellular matrices was studied in the distal interlobular arteries in the rat kidney, employing three different morphological techniques, including rhodamine-phalloidin staining of cryosections, resorcin-fuchsin staining of paraffin sections, and a cold dehydration procedure for electron microscopy. The endothelial cells possess longitudinally running stress fibers. The inner elastic layer is composed of meshworks of elastic fibers encompassing numerous pores. The smooth muscle cells containing abundant actin filaments are arranged circumferentially around the vascular axis. The endothelial stress fibers are found mainly in the basal half of the endothelial cells, and anchor onto the basal cell membranes. The elastic meshworks send off longitudinal branch fibers to contact the endothelial cell membranes at the anchoring sites of stress fibers. In addition circumferential branches run toward the smooth muscle cells. The functional significance of the intracellular contractile apparatus and the extracellular tensile component in small arteries was discussed.

Microtubules of Guinea Pig Cochlear Epithelial Cells

By tannic acid staining, the 13-protofilament composition of cochlear hair cell microtubules, an impressive contrast against the 15-protofilament microtubules in cochlear pillar cells, was verified. The 15-protofilament microtubules formed a large and stiff cytoskeletal bundle in pillar cell bodies involving abundant actin filaments. The bundles were always situated vertically, i.e., longitudinally to the cell body axis, and were most numerous in the outer as well as the inner pillar cells in the basal turn, decreasing gradually toward the apex. Such gradient architecture of the pillar cell cytoskeleton can be correlated with the tuning mechanism for traveling waves of sound containing variable frequencies.

Microtubule Subunits of Guinea Pig Vestibular Epithelial Cells

Guinea pig cochlear supporting cells have microtubules which are composed of 15, instead of the ordinary 13, protofilaments. The microtubules form a large and stiff bundle involving abundant actin filaments to provide effective rigidity to the cell specialized for transduction of extremely high-frequent mechanical stimuli. We examined microtubules in guinea pig vestibular end organs with the transmission electron microscopy after treatment with tannic acid. Solitary microtubules occurred abundantly in the supranuclear region of type I hair cells, but sparsely in type II hair cells. Individual microtubules consisted of an ordinary set of 13 protofilaments in these hair cells as well as in the supporting cells. Supporting cells were characterized by cytoskeletal bundles of 2 to 30 microtubules which were found to be connected with actin filaments via cross-linking units. Results from the present investigation indicate that such less-organized microtubules of 13 protofilaments are sufficient for vestibular supporting cells which are specialized for detection of lower-frequency vibration together with fellow sensory cells.

Computer-graphic design for human performance : Donald A. Topmiller and Nilss M. Aume. Proc. IEEE A. Reliab. Maintainab. Symp., Los Angeles, 17–19 January 1978, p. 385

The spatial distribution of the microtubules (MT) in the rat 3Y1 cells in mitosis was investigated by immunoelectron microscopy and computer-graphic reconstruction of serial thin sections. In anaphase the interzone-MT increased in number gradually with advancing phase, while the kinetochore-MT in half-spindles decreased. The interzone-MT overlapped with each other at the equatorial region of the cell, and they formed a specific structure called the ‘stem bodies’. The ends of the interzone-MT opposite to the stem bodies often attached to chromosomes but not to the poles. The stem bodies were not labeled with immunogold particles of anti-α tubulin. Some of the stem bodies or MT which originate from stem bodies were found just beneath the plasma membrane in the equatorial region where abundant actin filaments appear showing the formation of the contractile ring and subsequently the cleavage furrow begins. On the basis of these observations it is assumed that the interzone-MT is involved both in the separation of chromosomes in anaphase and in the formation of the cleavage furrow in telophase.