Differentiation of the rat epididymis after withdrawal of androgen

Summary The differentiation capacity of the rat epididymis after depletion of androgen was studied in organ culture and in castrated rats. The differentiation of narrow cells in 5- and 10-day-old explants and in 10-day-old castrated rats suggests that: (i) the testicular androgens are not essential for their differentiation, (ii) a differential androgen dependence exists among the epididymal cell types, (iii) the undifferentiated epithelial cells are the precursors of the narrow cells.     

A new cell wall structure in a symbiotic and a free-living strain of the blue-green alga genus Chroococcidiopsis (Pleurocapsales)

Freeze etching studies in a symbiotic and a freeliving strain of Chroococcidiopsis revealed a specific layer in the outer cell wall not described so far from Cyanophyta. The layer showed a complex organisation: The main unit are ribbons, 2–3 nm thick, striated at right angle to the longitudinal axis. They are interwoven to a patchwork-like leaflet. The ribbons are virtually composed of globular particles associated in parallel rows. The cytoplasmic membrane and the cell walls of the symbiotic and the free-living strain were compared.Abbreviations cm cytoplasmic membrane - CW 1,2,3 cell wall layer 1,2,3 - EF exoplasmic fracture face - PF protoplasmic fracture face     

Identification of candidate regulators of multipotency in human skeletal progenitor cells

Stem cell differentiation is controlled intrinsically by dynamic networks of interacting lineage-specifying and multipotency genes. However, the relationship between internal genetic dynamics and extrinsic regulation of internal dynamics is complex and, in the case of skeletal progenitor cell differentiation, incompletely understood. In this study we elucidate a set of candidate markers of multipotency in human skeletal progenitor cells by systematic study of the relationships between gene expression and environmental stimulus. We used full genome cDNA microarrays to explore gene expression profiles in skeletal progenitor enriched populations derived from adult human bone marrow, minimally cultured in basal, osteogenic, chondrogenic, and adipogenic lineage-specifying culture conditions. We then used a variety of statistical clustering procedures to identify a small subset of genes which are related to these stromal lineages but are specific to none. For a selection of 11 key genes, conclusions of the microarray study were confirmed using quantitative real-time PCR.     

PAR-6 levels are regulated by NOS-3 in a CUL-2 dependent manner in Caenorhabditiselegans

The PAR proteins have an essential and conserved function in establishing polarity in many cell types and organisms. However, their key upstream regulators remain to be identified. In C. elegans, regulators of the PAR proteins can be identified by their ability to suppress the lethality of par-2 mutant embryos. Here we show that a nos-3 loss of function mutant suppresses the lethality of par-2 mutants by regulating PAR-6 protein levels. The suppression requires the activity of the sex determination genes fem-1/2/3 and of the cullin cul-2. FEM-1 is a substrate-specific adaptor for a CUL-2-based ubiquitin ligase (CBC^FEM-1). Interestingly, we find that CUL-2 is required for the regulation of PAR-6 levels and that PAR-6 physically interacts with FEM-1. Our data strongly suggest that PAR-6 levels are regulated by the CBC^FEM-1 ubiquitin ligase thereby uncovering a novel role for the FEM proteins and cullin-dependent degradation in regulating PAR proteins and polarity processes.     

A strong nucleotypic effect on the cell cycle regardless of ploidy level

Background and Aims: In published studies, positive relationships between nucleotypeand the duration of the mitotic cell cycle in angiosperms havebeen reported but the highest number of species analyzed wasapprox. 60. Here an analysis is presented of DNA C-values andcell cycle times in root apical meristems of angiosperms comprising110 measurements, including monocots and eudicots within a settemperature range, and encompassing an approx. 290-fold variationin DNA C-values. Methods: Data for 110 published cell cycle times of seedlings grown attemperatures between 20–25 °C were compared with DNAC-values (58 values for monocots and 52 for eudicots). Regressionanalyses were undertaken for all species, and separately formonocots and eudicots, diploids and polyploids, and annualsand perennials. Cell cycle times were plotted against the nuclearDNA C-values. Key Results: A positive relationship was observed between DNA C-value andcell cycle time for all species and for eudicots and monocotsseparately, regardless of the presence or absence of polyploidvalues. In this sample, among 52 eudicots the maximum cell cyclelength was 18 h, whereas the 58 monocot values ranged from 8–120h. There was a striking additional increase in cell cycle durationin perennial monocots with C-values greater than 25 pg. Indeed,the most powerful relationship between DNA C-value and cellcycle time and the widest range of cell cycle times was in perennialsregardless of ploidy level. Conclusions: DNA replication is identified as a rate limiting step in thecell cycle, the flexibility of DNA replication is explored,and we speculate on how the licensing of initiation points ofDNA replication may be a responsive component of the positivenucleotypic effect of C-value on the duration of the mitoticcell cycle.     

Mechanics of circadian pulvini movements in Phaseolus coccineus L.

The circadian movement of the lamina of primary leaves of Phaseolus coccineus L. is mediated by antagonistic changes in the length of the extensor and flexor cells of the laminar pulvinus. The cortex of the pulvinus is a concentric structure composed of hexagonal disc-like cells, arranged in longitudinal rows around the central stele. Observations with polarization optics indicate that the cellulose microfibrils are oriented in a hoop-like fashion in the longitudinal walls of the motor cells. This micellation is the structural basis of the anisotropic properties of the cells: tangential sections of the extensor and flexor placed in hypotonic mannitol solutions showed changes only in length. As a consequence a linear correlation between length and volume was found in these sections. Based on the relationship between the water potential (which is changed by different concentrations of mannitol) and the relative volume of the sections and on the osmotic pressure at 50% incipient plasmolysis, osmotic diagrams were constructed for extensor and flexor tissues (cut during night position of the pulvinus). The bulk moduli of extensibility, , were estimated from these diagrams. Under physiological conditions the values were rather low (in extensor tissue below 10 bar, in flexor tissue between 10 to 15 bar), indicating a high extensibility of the longitudinal walls of the motor cells. They are strongly dependent on the turgor pressure at the limits of the physiological pressure range.In well-watered plants, the water potentials of the extensor and flexor tissues were surprisingly low,-12 bar and-8 bar, respectively. This means that the cells in situ are by no means fully turgid. On the contrary, the cell volume in situ is similar to the volume at the point of incipient plasmolysis: the cell volumes of extensor and flexor cells in situ were only 1.01 times and 1.1 times larger, respectively, than at the point of incipient plasmolysis, whereas at full turgidity (cells in water) the corresponding factors were 1.8 and 1.5. It is suggested that the high elasticity of the longitudinal walls, the anisotropy of the cell walls, and the low water potential of the sections which is correlated with slightly stretched cell walls in situ, are favourable and effective for converting osmotic work in changes in length of the pulvinus cells, and thus for the up and down movement of the leaf.Symbols volumetric elastic modulus - _i instantaneous volumetric elastic modulus - _i stationary volumetric elastic modulus - weight-averaged stationary bulk modulus of extensibility - ₀ osmotic pressure of the vacuole of a cell at the point of incipient plasmolysis - weight-averaged osmotic pressure of the vacuoles of the tissue at 50% incipient plasmolysis - water potential     

The fine structure of polychaete septate junctions

Summary Epidermal septate junctions of Nereis sp. and Cirriformia sp. fixed with OsO₄ or glutaraldehyde/OsO₄ display variable structure in electron micrographs. In transverse section the septa are often indistinct and obscured by opaque material that fills the junctional cleft. Septa (spaced at 180–280 Å) are more clearly defined in slightly oblique transverse section; they exhibit an electron lucent center and appear to be linked by arms. En face views of the junction show a honeycomb pattern. Cytoplasmic faces of junctional membranes are backed with plaques opposite the septa. Lanthanum used as a tracer delineates junctional structure in negative contrast. In transverse section a chain-like lattice is present in the junctional cleft. En face views show parallel rows of pleated elements often linked by arms into honeycomb arrays. Oblique sections demonstrate that these pleated elements are continuous with the chain-like lattice seen in transverse sections. Lanthanum does not pass entirely through the junction. Lanthanum reveals that the septa have a very intricate substructure, but it is difficult to visualize the architecture that could generate the various images presented by these junctions when seen in different orientations. However, it is clear that these junctions possess some features that are diagnostic of several supposedly different types of septate junctions in invertebrates.Supported by USPHS grants NIH 5 P01 NS-07512, NIH 2701 GM-00102, and NB-00840, and by a grant from the Pomona College Research CommitteeI thank Sarah Wurzelmann, Stanley Brown, Nancy Kelly, and Gerhard Ott for excellent technical assistance. Portions of this study were carried out while I was a Postdoctoral Fellow in the Department of Anatomy, Albert Einstein College of Medicine. I dedicate this article to Berta Scharrer as a token of appreciation and affection for her guidance, encouragement, inspiration, and example of excellence     

The goldfish pituitary

Summary In the goldfish, Carassius auratus, morphological and functional aspects of the pituitary gland were studied at the ultrastructural level and six cell types could be distinguished in the pars distalis. Acidophilic cells of the rostral pars distalis were identified as prolactin cells, the chromophobic cells of the rostral pars distalis as ACTH cells, the non-globular basophilic cells of the rostral and the proximal pars distalis as TSH cells, the globular basophils of the proximal pars distalis as gonadotropic cells and the acidophils of the proximal pars distalis as somatotrophs.Besides some of the well established criteria of morphological and functional identification of different cell types, two new approaches have been used in the present study. One was to express the electron density of secretory granules objectively by means of a photometric method. It was found that both types of acidophilic cells which produce the proteohormones prolactin and somatotropin respectively, had granules with the highest electron densities. The basophilic cells producing the glycoproteins gonadotropin and TSH respectively, possessed granules of intermediate electron density whereas the chromophobic cells storing the peptide hormone ACTH had granules of lowest densities. The second new approach was the administration of the synthetic mammalian releasing hormones LH-RP and TRF, which helped in identifying gonadotropic and thyrotropic cells respectively. In the goldfish there is evidence for the presence of only one type of gonadotropic cell.Supported by a grant of the Science Research Council of Great Britain to Professor Sir Francis Knowles, F.R.S. The electron microscope used was provided by the Medical Research Council of Great Britain. The integrating photometer IPM2 was kindly on loan from Messrs. Carl Zeiss, Oberkochen, Germany. For technical advice we are greatly indebted to Mr. P. K. Kaul, B. E., M.I. Struct. E., C. Eng.     

Analyse quantitative des remaniements intestinaux et évolution de la synthese de l'ADN

Résumé Les remainements intestinaux affectant la paroi intestinale sont quantifiés chez les larves d'un Amphibien Anoure,Alytes obstetricans, traitées par la thyroxine. La fraction correspondant à chaque zone composant la paroi est déterminée sur coupe. La répartition et la fréquence des noyaux marqués sont recherchées chez des larves ayant reçu de la thymidine tritiée.L'indice de marquage nucléaire de l'épithélium primaire tend vers zéro durant les 3 premiers jours du traitement. Ces résultats reflètent un ralentissement de la croissance du tissue, précédant sa dégénérescence et son élimination complète au 14ème jour d'immersion dans la solution hormonale.Dès de 3ème jour de traitement, un épithélium secondaire se développe à partir de cellules-souches basales. Son indice de marquqge croît, culmine au 9ème jour avec une valeur proche de 50%, puis s'abaisse. La prolifération cellulaire est plus modérée dans la zone extra-épithéliale, qui s'épaissit toutefois au cours de cette métamorphose provoquée.

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Quantitative analysis of intestinal changes and the evolution of DNA synthesis in thyroxine-treated larvae ofAlytes obstetricans. (Amphibia, Anura)

Summary Changes in the intestinal wall ofAlytes obstetricans (Amphibia, Anura) were quantified during thyroxine treatment. The relative proportion of each intestinal wall component was determined in tissue sections. Autoradiographic studies on intestine with³H-thymidine revealed the distribution and frequency of labeled nuclei.The labeling index in the primary epithelium falls to zero by 3 days. Thyroxine treatment induces a decrease in the growth rate of this tissue, just before its degeneration and complete elimination by 14 days.Three days after T₄-treatment, a secondary epithelium develops from basal stem cells. Its labeling index rises to a maximum of about 50% by 9 days, and thereafter declines. Cell proliferation is less marked in the extraepithelial zone, which nevertheless thickens during this thyroxine-induced metamorphosis.