SOME ASPECTS OF SIEVE CELL ULTRASTRUCTURE IN PINUS STROBUS

The immature sieve cell of Pinus strobus contains all of the protoplasmic components commonly encountered in young cell types. In addition, it contains slime bodies with distinct double-layered limiting membranes. The mature sieve cell is lined by a narrow layer of cytoplasm consisting of a plasmalemma, one or more layers of anastomosing tubules of endoplasmic reticulum, numerous mitochondria, starch granules and crystal-like bodies. Each mature cell contains a necrotic nucleus. Ribosomes and dictyosomes are lacking. Strands derived ontogenetically from the slime bodies of the immature cell traverse the central cavity and are continuous with those of neighboring sieve cells through the plasmalemma-lined pores of the sieve areas. Sieve-area pores are also traversed by numerous endoplasmic membranes. A membrane was not found separating the parietal layer of cytoplasm from the large central cavity.     

Gross,histological and ultrastructural morphology of the aglomerular kidney in the lined seahorse Hippocampus erectus

Histologic evaluation of the renal system in the lined seahorse Hippocampus erectus reveals a cranial kidney with low to moderate cellularity, composed of a central dorsal aorta, endothelial lined capillary sinusoids, haematopoietic tissue, fine fibrovascular stroma, ganglia and no nephrons. In comparison, the caudal kidney is moderately to highly cellular with numerous highly convoluted epithelial lined tubules separated by interlacing haematopoietic tissue, no glomeruli, fine fibrovascular stroma, numerous capillary sinusoids, corpuscles of Stannius and clusters of endocrine cells adjacent to large calibre vessels. Ultrastructural evaluation of the renal tubules reveals minimal variability of the tubule epithelium throughout the length of the nephron and the majority of tubules are characterized by epithelial cells with few apical microvilli, elaborate basal membrane infolding, rare electron dense granules and abundant supporting collagenous matrix.     

The distal nephron in the chick embryo as a target tissue for 1-alpha-25-dihydroxycholecalciferol

A histological and ultrastructural study as well as an autoradiographic analysis after injection of tritiated 1,25-dihydroxycholecalciferol (1,25-DHCC) were conducted on the distal convoluted tubules of chick embryos. Distal tubules in the embryo were shown to have the same spatial distribution as described for the adult kidney; they presented a convoluted portion located in the vicinity of the central intralobular veins and straight portions irradiating from this region towards the periphery. The epithelium in these tubules was well differentiated; its cells had numerous interdigitating folds in their lateral boundaries which were especially numerous at the basal ends. This device greatly increased the membrane surface available for interchange and was interpreted as an expression of active water and/or mineral transport. Nuclear concentration of radioactivity was found 2 h after injection of tritiated 1,25-DHCC in both the pars convoluta and the pars recta of the distal tubules. This concentration could be blocked by the previous administration of large amounts of nonradioactive 1,25-DHCC. These facts were interpreted as indicating that distal convoluted tubules in the chick embryo are functionally differentiated and contain target cells for 1,25-DHCC.     

FINE STRUCTURE OF THE RETINULAE IN THE COMPOUND EYE OF THE HONEY-BEE

The retinula of the compound eye of the worker honey-bee has been examined with the electron microscope. The rhabdom lies on the ommatidial axis; it is usually cylindrical in shape, about 3 to 4 µ in diameter, and lacks an axial cavity. Cross-sections show it to be four parted, although it is formed from eight retinular cells (Figs. 2, 3). Each quadrant of the rhabdom consists of a closely packed parallel array of tubules with long axes perpendicular to the axis of the rhabdom. The tubules in adjacent quadrants of the rhabdom are mutually perpendicular. At the distal end of the ommatidium these tubules are seen to be microvilli of the retinular cells. Immediately surrounding the rhabdom, the cytoplasm of the retinular cells contains a membranous endoplasmic reticulum which is oriented approximately radially with respect to the axis of the ommatidium. Farther away from the rhabdom the cytoplasm contains numerous mitochondria.     

Buccal glands of adults of the lamprey Mordacia mordax,including comparisons with other species

Mordacia mordax is one of the two anadromous parasitic lamprey species of the southern hemisphere family Mordaciidae. Its adults possess two lateral buccal glands and one central buccal gland. When the tongue-like piston is retracted, the buccal glands occupy much of the opening of the oral cavity at the rear of the buccal cavity. The glands contain numerous tube-like, ductless secretory units, which discharge directly into the buccal cavity. Their secretory epithelial cells contain numerous granules, some of which are zymogen-like, while others have a beaded, spiralled appearance. The similarity of the latter to mast cell granules suggests that they may likewise produce an anticoagulant, which would be valuable to a presumed blood feeder such as M. mordax. The mucus produced by these cells could act as a carrier for the secretions and as an adhesive for promoting retention of t he secretions on the host's surface. When the young adults is transferred to salt water, the buccal glands increase their production and discharge of secretions. Since the glands are not enclosed in musculature, their secretions are probably discharged by mechanical pressure applied by the forward movement of the head of the tooth-bearing piston into the buccal cavity. An account is given of the way in which the location, number, glandular organization, secretory granules, and type of secretion of the buccal glands of M. mordax, and thus presumably also their mode of function, differ markedly from those of members of the other lamprey family found in the southern hemisphere, and of all holarrctic lampreys. © 1995 Wiley-Liss, Inc.     

Regulation of Krüppel expression in the anlage of the Malpighian tubules in the Drosophila embryo

The expression of most Drosophila segmentation genes is not limited to the early blastoderm stage, when the segmental anlagen are determined. Rather, these genes are often expressed in a variety of organs and tissues at later stages of development. In contrast to the early expression, little is known about the regulatory interactions that govern the later expression patterns. Among other tissues, the central gap gene Krüppel is expressed and required in the anlage of the Malpighian tubules at the posterior terminus of the embryo. We have studied the interaction of Krüppel with other terminal genes. The gap genes tailles and huckebein, which repress Krüppel in the central segmentation domain, activate Krüppel expression in the posterior Malpighian tubule domain. The opposite effect on the posterior Krüppel expression is achieved by the interposition of another factor, the homeotic gene fork head, which is not involved in the control of the central domain. In addition, Krüppel activates different genes in the Malpighian tubules than in the central domain. Thus, both the regulation and the function of Krüppel in the Malpighian tubules differ strikingly from its role in segmentation.     

The ultrastructure of secretion in the spermatheca of the salamander, Manculus quadrigitatus (Holbrook)

Spermathecae of mature salamanders (Manculus quadridigitatus) were studied by light and electron microscopy. Gross morphology exhibits a complex of muscle, connective tissue and pigment cells surrounding a cluster of tubules, which empty into a ciliated central duct leading to the cloacal cavity. The tubules are composed of myoepithetial cells and secretory cells, anchored to an encompassing basal lamina. Secretion products appear to be initiated as crystalline deposits, seen in mitochondrial repositories, which are subsequently sequestered in the perinuclear region. Observations show these vesicles to be precursors of the Golgi synthesis of carboxylated polysaccharides, as determined by histochemical tests using toluidine blue, ruthenium red, and alcian blue. The secretory products are emptied into the tubule lumen. thereby bathing the stored sperm and maintaining them in a viable state for approximately 8 months. The storage tubules appear to be a complete complex of varying epithelial cells specifically designed to support viable sperm and to resorb non-functional forms.     

The structure of the nerve fibre layer and neurocord in the enteropneusts

Summary The nerve fibre layer and the neurocord of the Enteropneusts Saccoglossus horsti, Harrimania kupfferi and Ptychodera flava have been examined with the electron microscope. The nerve fibres vary in diameter between 0.15 to 10 m. The majority of the fibres are of the smaller diameters. The nerve fibre layer is intraepidermal, and is divided by processes running radially from the epithelial cells to the basement membrane that separates the nerve fibre layer from the muscle cells.The cells of origin of these nerve fibres are situated mainly in the innermost layers of the epidermal cells. The nerve fibre profiles contain numerous vesicles of very varied diameter and contents, together with larger granular inclusions that are also found in the nerve cell bodies.Morphologically recognisable synapses are rare, but the majority of fibres are in intimate contact with one another. Sometimes the mass of fibres is divided into bundles by the epithelial cell processes. The majority of giant fibres are situated near to the basement membrane of the neurocord. The giant fibres also have a varied content of vesicles as well as neurofilaments and neurotubules.The central canal in Ptychodera flava and the remnants of the central canal in Saccoglossus horsti are both lined by columnar cells that bear microvilli as well as cilia with the typical 9 + 2 pattern of tubules. Scattered amongst these cells are mucus secreting cells which open into the cavity of the canal.I (P.N.D.) should like to thank Professor J. Z. Young, F. B. S. for much advice and encouragement. Dr. R. Bellairs generously provided the electron microscope facilities, and Dr. R. Newell kindly collected and identified the Saccoglossus specimens. Mr. R. Moss, Mrs. J. Hamilton and Mr. A. Aldrich gave excellent technical and photographic assistance.     

Evidence and bioassay for diuretic factors in the nervous system of larvalHeliothis virescens

Summary Diuretic factors were studied in the central nervous system of larvae of the tobacco budworm,Heliothis virescens, using [¹⁴C]urea as a sensitive indicator for water movement through isolated Malpighian tubules. The assay required Na⁺ and a pH of 6.0–6.2 for maximum activity. Malpighian tubules had high secretory activity in feeding larvae of the fifth instar, but the activity declined during the burrowing-digging stage that preceded pupation. Malpighian tubules from starved larvae showed a greater response to extracts of nervous tissues than did tubules from feeding larvae, and extracts showed a dose-response relationship with fluid secretion. Diuretic activity was distributed throughout all parts of the central nervous system with the brain having the most activity. Brain extracts increased fluid secretion by in vitro Malpighian tubules by more than 3-fold and doubled the rate of dye clearance from the hemolymph in vivo. Diuretic activity in nervous tissue extracts was unaffected by boiling but sensitive to proteases. Fluid secretion by in vitro tubules was increased by cAMP, dbcAMP, theophylline, octopamine and dopa. These studies provide evidence for the presence of diuretic factors in the central nervous system ofH. virescens larvae and describe a sensitive bioassay for these factors.Abbreviations AR activation ratio - cAMP cyclic AMP - dbcAMP dibutyryl cyclic AMP - dbcGMP dibutyryl cyclic GMP - Dopa dihydroxyphenylalanine - 5-HT 5-hydroxytryptamine - L1 larval instar - VCNS ventral central nervous system     

The ultrastructure and development of tubular and crystalline P-protein in the sieve elements of certain papilionaceous legumes

Summary The ultrastructure of the primary sieve elements of several papilionaceous legumes was studied using hypocotyl and young internode segments fixed in glutaraldehyde followed by osmium tetroxide. In particular, the study sought to determine whether the crystalline flagellar inclusions characteristic of these species are developmentally related to the P-protein bodies present in the phloem of these and other legumes and of angiosperms generally. The crystalline inclusions consist of a central body terminated at one or both ends by a gradually tapering tail. The central body is usually spindle shaped in longitudinal section and square in cross section. In all species examined, the inclusion is first seen as a small, thin crystal in the cytoplasm of young sieve elements. The crystal enlarges and acquires tails as the sieve element develops. In certain species, exemplified byDesmodium canadense, numerous tubules are formed in the cytoplasm near the crystal and appear to be concerned in its growth. The observations on the structure and interactions of these two components, tubules and crystalline inclusions, suggest that both represent forms of P-protein: the tubules are continuous with the crystal and are striated like the crystal near the tubule-crystal junction, suggesting that they are adding onto the crystal body; the tubules closely resemble the P-protein tubules described in the literature in that they measure 157 Å in diameter, accumulate in spindle-shaped bundles, and disperse into striated fibrils late in the ontogeny of the sieve element; and finally, the crystal also disperses into fine filaments. The crystalline inclusion therefore probably represents still another aggregation state of P-protein, one that is characteristic of papilionaceous legumes. The different stages of crystal aggregation and the diverse forms of P-protein now known are discussed briefly in relation to the control of macromolecular assembly and subunit packing.     

Impermeability of hagfish cerebral capillaries to horseradish peroxidase

Summary Brain capillaries and their permeability to intravenously injected horseradish peroxidase, HRP, (MW: 40,000) were examined electron-microscopically in an attempt to find a structural explanation for the poorly developed blood-brain barrier in the hagfish, Myxine glutinosa. In particular, it was the aim of this study to examine the role of the numerous endothelial vesicles and tubules in the transport of this tracer between blood and brain. Many of the vesicles and tubules were found to be in continuity with the luminal or abluminal surfaces, but tubules generating channels through the endothelial cells were never observed. The cleft between adjacent endothelial cells was obliterated by punctate junctions. HRP, which was allowed to circulate for up to 35 min, was not found in the basal lamina or in the surrounding brain parenchyma. Few of the luminal vesicles and tubules were marked by the tracer. In the intercellular cleft HRP was stopped by the junctions. It is concluded that the hagfish like other vertebrates has a blood-brain barrier to HRP, and the numerous vesicles and tubules occurring in hagfish brain endothelium are not involved in the transendothelial transport of this macromolecule.     

Fine Structure and Behaviour of the So-called Cuvierian Organs in the Holothuroid Genus Actinopyga (Echinodermata)

Abstract Actinopygid Cuvierian tubules are few in number. They are made of a basal trunk from which arises 2–3 branches. The trunk is smooth and hollow (proximally) or slightly swollen and solid (distally) and the branches consist of a central rachis to which attach many peripheral spherules. The fine structure of the tubules is similar in the three investigated species of Actinopyga but differs considerably from that of non-actinopygid tubules. Basic behavioural differences occur also as actinopygid Cuvierian tubules cannot elongate nor become sticky, and are not expelled by the individuals. It is concluded that actinopygid Cuvierian tubules do not fulfil a defensive function.     

Ultrastructural modifications of the glandular epithelium of the receptaculum seminis in Thermobia domestica (Insecta: Thysanura) during the moulting period

Summary The wall of the receptaculum seminis of Thermobia domestica is composed of numerous glandular units, each with four enveloping cells (denoted 1 to 4) separated by ordinary epithelial cells and associated with a cuticular apparatus. During the moulting periods, which continue to occur in the adult stage, these cells undergo a series of transformations. Just before apolysis there is a dedifferentiation of numerous cytoplasmic organelles, but no mitosis has been observed. When the intima lifts off, the apical system of each glandular unit, i.e. the distal parts of the C2 and C3 cells surrounding the end apparatus, is also eliminated. Then at the apex of each glandular unit, a new ductule is formed in the cavity of which a long ciliary process grows up from cell C1. Finally comes the phase of cuticle formation, i.e., epicuticle for the ductules, epi-and endocuticle for the intima lining the central cavity of the receptaculum. Various cell types participate in secretion of cuticle, the ciliary cells (C1) being responsible for the formation of the porous end apparatus. At ecdysis almost all of the new intima has been secreted and the apical systems are once more differentiated. These transformations are compared with those recently described in other exocrine glands of arthropods, e.g., tegumentary glands and accessory glands of the genital ducts.     

On a Peculiar Mode of Germ-Layer Formation

In some planulae of the alcyonarian Gersemia rubiformis an interior structure was found in the entodermal cavity. It consisted of two layers separated by a basement membrane, the inner layer facing a central cavity. The outer layer was structurally identical with the inner “entomesoderm” of the body wall, while the inner layer of the “ball” was provided with numerous cilia and a brushborder. The development of the interior structure is described as appearing from the structural findings in different planulae. This development is very different from any other developmental process described so far.     

Fine structure of the posterior salivary gland ofEledone cirrosa andOctopus vulgaris

Summary The posterior salivary gland of Octopods comprises a parenchyma of branching tubules in a connective tissue stroma. The tubules are lined by either of two distinct epithelia.Type A is composed predominantly of columnar cells containing large granules whose contents vary in appearance from cell to cell.Type B consists of three cell types: A circumferential layer of processes ofstriated cells containing radially orientated infoldings of the cellular membrane, between which are packed numerous mitochondria;cistern cells which contain an invaginated system of membrane loops, the interior of which is in communication with the lumen; andlumen lining cells. All these cells send processes to the basement membrane of the tubule, so that both epithelia are pseudostratified. The functional significance of this cytological specialisation is discussed.Thanks are due to Prof. J. Z. Young F. R. S. and Prof. E. G. Gray for helpful discussion and use of facilities during the course of this study, and to Prof. Young for the loan of the Cajal preparations. I also wish to thank Miss E. Franke for excellent technical assistance.     

An immunocytochemical study of pulpal responses to cavity preparation by laser ablation in rat molars by using antibodies to heat shock protein (Hsp) 25 and class II MHC antigen

Initial responses of odontoblasts and immunocompetent cells to cavity preparation by laser ablation were investigated in rat molars. In untreated control teeth, intense heat shock protein (Hsp) 25 immunoreactivity was found in the cell bodies of odontoblasts, whereas cells immunopositive for the class II major histocompatibility complex (MHC) antigen were predominantly located beneath the odontoblast layer in the dental pulp. Cavity preparation caused the destruction of the odontoblast layer and the shift of most class-II-MHC-positive cells from the pulp-dentin border toward the pulp core at the affected site. Twelve hours after cavity preparation, numerous class-II-MHC-positive cells appeared along the pulp-dentin border and extended their processes deep into the exposed dentinal tubules, but subsequently disappeared from the pulp-dentin border together with Hsp-25-immunopositive cells by 24 h after the operation. By 3–5 days postoperation, distinct abscess formation consisting of polymorphonuclear leukocytes was found in the dental pulp. The penetration of masses of oral bacteria was recognizable in the dentinal tubules beneath the prepared cavity. These findings indicate that cavity preparation by laser ablation induces remarkable inflammation by continuous bacterial infections via dentinal tubules in this experimental model, thereby delaying pulpal regeneration.This work was supported by Grant-in-Aid for Scientific Research to promote 2001-Multidisciplinary Research Projects in 2001–2005, and KAKENHI (C) (nos. 12671765 and 14571727 to H.O.) from MEXT     

Fine structure of the chromatoid body during spermatogenesis in the water-strider,Gerris remigis (SAY)

Summary During spermatogenesis in Gerris remigis, chromatoid bodies appear in the spermatocytes and persist to the-mid-spermatid stage. These structures consist of numerous, parallel tubules, which measure approximately 500 Å in diameter. The tubules are arranged in hexagonal array, and contain dense granules that resemble ribosomes. The chromatoid body may be secretory in function, or may be involved in intracellular transport.The technical assistance of Mr. Roy R. Keppie and Mrs. Mona Brandreth is gratefully acknowledged.     

Ultrastructure of Spermatozoa in the Nematode Halalaimus dimorphus (Nemata: Oxystominidae)

The ultrastructure of spermatozoa in the free-living marine nematode Halalaimus dimorphus was studied with transmission electron microscopy. Spermatozoa in the posterior testis of the male had a large cavity filled with cellular processes, which contained a variable number of small tubules. Mitochondria and small tubules were the only cell structures observed in the cytoplasm. The spermatozoa had a bipolar structure. The anteriorly situated nucleus, which was electron-dense and homogeneous, was surrounded by a single membrane. The size of the small tubules in the cytoplasm (diam. 12-13 nm) and their relatively thick wall structure suggested that they were not normal microtubules (diam. 25 nm). The material of the small tubules was assumed to be major sperm protein (MSP). The cavity appeared to open on the surface of the spermatozoon at the posterior extremity of the cell, and also medially, at the level of the anterior end of the cavity. The pores apparently were closed by a special plug-like structure, which was an evagination of the cell. The wall of the cavity was characterized by longitudinal folds, which were mushroom-shaped in transverse section. Spermatids in the anterior testis of H. dimorphuswere characterized by fibrous bodies packed with small tubules and by cellular processes also containing small tubules. H. dimorphus sperm seem to perform swimming movements based on liquid currents commonly present in turbin-like systems. Spermatogenesis resembled that found in ticks.     

Observations on the relationship between “chloride-type” and “pseudobranch-type” cells in the gills of a fish,Oligocottus maculosus

Summary Chloride cells in gill epithelium of Oligocottus maintained in sea water have a much branched system of agranular cytoplasmic tubules, numerous mitochondria, and a prominent apical crypt. The mitochondria are randomly dispersed and do not show preferential orientation with respect to the tubules.After brief exposure of fish to sea water diluted 1/100 with glass distilled water, the mitochondria and tubules become rearranged into parallel arrays and the apical crypts disappear. The appearance of these cells is similar to that of pseudobranch cells in Fundulus heteroclitus (Copeland and Dalton, 1959).These data suggest that chloride cells and pseudobranch cells represent different adaptive forms of a single cell type and that transformation from the chloride cell configuration to that of pseudobranch cells can be induced by osmotic stress.This work was performed in 1963 when the author was enrolled in the Fine Structure Training program of the Department of Biological Structure, University of Washington. Financial aid was provided by the United States Public Health Service (Grant No. 5T1 GM-136).     

Subunits of flagellar accessory tubules

Many sperm flagella contain a central pair of singlet tubules surrounded by nine doublet tubules. Insect sperm flagella, however, usually contain in addition to the typical 9+2 arrangement of tubules, an additional row of nine singlet tubules which are called accessory tubules. Each of these accessory tubules in the Colorado potato beetle (Leptinotarsa decemlineata (Say)) contains a single central prototubule surrounded by an array of 15 or 16 peripheral prototubules. The number of prototubules in the accessory tubules of Leptinotarsa decemlineata was determined with an electron microscope and image details were reinforced by the rotation techniques of Markham.