Connecting Piece Research Articles

Spermatogenesis in animals as revealed by electron microscopy. XXVII. Development of the neck region and flagellum of the cat spermatozoon.

The first indication of differentiation of the Jensen's ring has been detected in an early stage of spermiogenesis of Felis catus Linne when the pair of centrioles takes up a position immediately beneath the plasma membrane. The chromatoid bodies appear in the early spermatid cytoplasm through the nuclear pore complex. In a more advanced stage, such bodies have been found in association with the striated columns, the distal centriole or the proximal part of flagellum and the Jensen's ring. As the spermiogenesis proceeds, the bodies have decreased their size and density, and finally disappear in mature spermatozoa. The chromatoid bodies seem, therefore, to share with the centriole the capacity to form the connecting piece. As a consequence of disorganization of triplet microtubules of the centriole, a noticeable material appears in the center of lumen of the centriole to be identifiable as a distinct precursor of the central pair of axonemal complex. Microtubules are first developed as the sheath of principal piece of the sperm flagellum, originating from the plasma membrane surrounding the axonemal complex.

Fine structural modifications of the rat chromatoid body during spermiogenesis

AbstractThe chromatoid body of rat spermatocytes and spermatids was studied with routine electron microscopy and the PA‐silver method for detection of glycoproteins. The chromatoid body consists of a membrane‐free aggregate of electron dense, finely filamentous material, in association with small vesicles. In late pachytene spermatocytes, there may be more than one chromatoid body; its dense component is diffusely reticulated. In young spermatids, there is only one chromatoid body per cell; the dense component is fairly compact, but it encloses less dense areas continuous with the cytoplasm. Within the less dense areas, as well as at the periphery of the dense component, small (400–800 Å) oval or tubular vesicular structures are observed whose contents exhibit a positive reaction for glycoprotein in PA‐silver stained sections. When the spermatid nucleus begins to elongate, the chromatoid body takes the form of an arc around the axial filament proximal to the centriolar apparatus. Soon thereafter, the bulk of the chromatoid body condenses into a sphere of very dense filamentous material surrounded by a corona of enlarged glycoprotein‐containing vesicles. In the later stages of spermiogenesis, the chromatoid body migrates away from the nucleus and disintegrates by fragmentation. It is noted that the chromatoid body undergoes its major morphological changes, possibly indicative of its active phase, while located in the para‐centriolar region, at the time when the nucleus elongates, and the connecting piece and ring of the spermatid are formed.

Scanning electron microscopy of the rat retina.

Fixed and unfixed, freeze-dried pieces of isolated retina and the posterior part of the eye bulb from adult rats were examined in a scanning electron microscope. The inner limiting membrane shows distinct cell borders, protrusions, and scattered microvilli-like structures. Different types of nerve cells are observed in the ganglion cell layer and the inner nuclear layer. They all lack synaptic boutons on the surface of their perikarya. There is an intercellular space between the processes in the nerve fiber layer. The inner and outer segments are surrounded by a space with extracellular material. Their surface is smooth or slightly undulated. There is no evidence indicating the existence of basal infoldings continuous with the membraneous structures inside the rod outer segments. The connecting piece between the inner and outer segments resemble a symmetrically shaped hour-glass. The surface of the epithelial cells is covered by microvilli forming a honeycomb-like structure and each outer segment is surrounded by several microvilli. The results obtained are discussed in relation to those obtained by transmission electron microscopy. The probable existence of a significant extracellular space and the distribution of extracellular material between the segments and the microvilli are discussed.

Relationship between nucleolus and nuclear bodies in human mixed salivary tumors

The ultrastructure of nuclear bodies in human mixed salivary tumors is described in three-dimensional reconstructions. These bodies are present both in close proximity to the nucleolus as well as far from it. In the first case a dense central zone has been found directly related to the nucleolus through a connecting piece. In the second case, these bodies have a clear central zone containing microtubule-like structures, vesicles, and filaments. The transitional stages from one variety to the other is suggested. The dense central zone is granular in its structure and is extractable with cold perchloric acid in the same way as the nucleolus. The morphology, cytochemistry, and probable determining factors of these bodies are discussed in relation to similar observations reported in plant, animal, and human tissues under normal and experimental conditions.

The fine structure and development of the neck region of the mammalian spermatozoon.

AbstractThe cross‐striated connecting‐piece in the neck region of the mammalian spermatozoon develops from material that seems to arise between the triplets in the wall of both proximal and distal centrioles. The precursor material extends radially from the centrioles and polymerizes around them to form the connecting piece. This is not composed of “segments” or “lamellae” as usually described but is a cross‐striated fibrous protein with a major period of 665 A and a complex pattern of intraperiod bands. It is considered to be homologous with the striated rootlets of cilia.During differentiation of this region, the proximal centriole develops at one end, a cylindrical prolongation which is similar in its structure but not identical with the centriole proper. This centriolar adjunct is a transient structure. The proximal centriole persists in the mature spermatozoon, but the distal centriole disintegrates during formation of the connecting‐piece.The outer dense fibers of the flagellum and the cross‐striated columns of the connecting piece are distinct components which arise separately and secondarily become continuous. The dense fibers originate as ridge‐like radial outgrowths from the wall of the corresponding doublets in the axonemal complex. As they enlarge they separate from the doublets throughout most of their length but they remain continuous with them at their distal ends.

Fine Structure of the Connecting Piece of the Spermatozoon

Past studies have demonstrated that the connecting piece of the mammalian spermatozoon consists of several components; namely, the “proximal” centriole, the segmented columns, the fibrils of the axial filament complex, and mitochondria. Little is known, however, of the anatomical and functional relations which bind these structures together. This prompted us to investigate the structural organization of the connecting piece by means of tridimensional studies on thin sections of human and rabbit spermatozoa from testis and epididymis.The connecting piece has the shape of an inverted cone. At its base lies the proximal centriole which is inclined at an angle of about 45° to the long axis of the flagellum. The nine dense fibers of the flagellum are continuous with the segmented columns (Figs. 1 and 4) which form the wall of the connecting piece. Fusion of fibers 9, 1 and 2 on one side (Fig. 3), and 5 and 6 on the other induces formation of two major segmented elements and reduces to six the total number of columns. However, the nine original columns become reconstituted at the proximal end of the connecting piece where the fused elements of the major columns separate again.

Studies on the receptors in the cerebral vesicle of the ascidian tadpole. 2. The ocellus

ABSTRACT Electron microscope observations of the photoreceptor of the tadpole larva of Ciona intestinalis show the ocellus to consist of about 10 cells. It is made up of 3 parts: a pigment cup, a lens system, and a retina. A single cup-shaped cell filled with membrane-bound pigment granules lies between the lens and the retinal cells. Part of the lens cell is contained within its concavity. The pigment granules are arranged to keep stray light from falling upon the photoreceptor endings. The lens system has 3 lens vesicles arranged in a line along the main axis of the pigment cup cell. The spherical vesicles are usually contained within a single cell. Each vesicle is separated from the rest of the lens cell cytoplasm by a single-layered sphere of mitochondria. No membrane separates the vesicle contents from the rest of the lens cell cytoplasm. The retinal cells lie above the dorsal arm of the pigment cup cell, and have tubular processes that pass through it to end as piles of membranes closely applied to the lens cell. Morphologically the photoreceptor units of the ascidian tadpole closely resemble the visual cells of the vertebrates, the piled photoreceptor membrane corresponding to the outer segment of the vertebrate rod cell and the tubular part to the connecting piece of a retinal rod.

PHOTORECEPTORS IN THE AMPHIBIAN FRONTAL ORGAN

The frontal organ (stirnorgan or Stieda's organ) of frogs and toads has long been a physiological enigma, as has likewise its reptilian homologue, the parietal eye. Some investigators have suggested that the stirnorgan is sensory,l others that it is secretory;2^ 3 still others4 5 have found no evidence of either function. This study of the frontal organ in the tadpole of the Pacific Treefrog, Hyla regilla, indicates that it is photoreceptive. Ultrastructure.-Electron microscopy of the stirnorgan of young larvae of H. regilla by Eakin and Westfall6 reveals processes, extending into its tiny lumen, which are structurally similar to those of rods and cones in the retina of the lateral eye and to those recently discovered in the parietal eye of lizards.7-' Figure 1 shows a longitudinal section of one of these processes. The outer segment (os) contains an array of about 135 discs (d) or laminae formed apparently by infoldings of the surface membrane (see arrows). In this feature the outer segment resembles that of cones in the lateral eye of the anuran Xenopus laevis.ll Many of the processes, such as the one figured, are short, stout, and bent in contradistinction to the long, straight filamentous outer segments of rods and cones of the vertebrate lateral eye and of receptors in the parietal eye. The inner segment (is), of which the distal part only is shown in Figure 1, contains many large elongate mitochondria (m) densely packed near the distal end of the segment as they are in the comparable region, the ellipsoid, of known photoreceptors; lipid droplets which are sometimes very large; osmiophilic granules (g, Fig. 2); and vesicles (v) of diverse sizes, some (see Fig. 2) reaching a diameter of 1A and containing material (secretion?) slightly more electron dense than the surrounding cytoplasm. The connecting piece, a short, narrow part of the process joining inner and outer segments, is not shown in Figure 1 because the plane of section is to one side of it. Figure 2, however, illustrates the connecting piece (cp) of another process. A fibrillar apparatus, presumably derived from that of a cilium of an ependymal cell, arises from a basal granule or axial centriole (cl) situated at the tip of the inner segment, passes through the connecting piece, and fans out into the clear matrix (s) of the outer segment. The apparatus is composed of nine peripheral fibrils (count based upon other micrographs), parts of which may be observed (f, Fig. 2). Adjacent to the axial centriole lies the oblique centriole, a short cylinder which appears in cross section (c,, Fig. 2) to consist of nine peripheral fibers. Stirnorganectomy.-Although the fine structure of the processes of the frontal organ just described is remarkably similar to that of rods and cones, evidence of light sensitivity is needed before the cells which bear them are designated photoreceptors. Bagnaral2 recently observed that the destruction of the epiphysis in tadpoles of Xenopus laevis eliminates the blanching reaction of the skin (concentration of pigment in the dermal melanophores of the body) commonly exhibited by amphibian larvae when placed in the dark. The frontal organ is known to be connected to the epiphysis by a nerve or pineal tract. -4 '3 I have traced it in larvae of H. regilla

A PERFORATED ENDOTRACHEAL CONNECTION PIECE

A PERFORATED ENDOTRACHEAL CONNECTION PIECE