Isolation and characterization of full-length chromosomes from non-culturable plant-pathogenic Mycoplasma-like organisms

We describe the isolation and characterization of full-length chromosomes from non-culturable plant-pathogenic, mycoplasma-like organisms (MLOs). MLO chromosomes are circular and their sizes (640 to 1185kbp) are heterogeneous. Divergence in the range of chromosome sizes is apparent between MLOs in the two major MLO disease groups, and chromosome size polymorphism occurs among some related agents. MLO chromosome sizes overlap those of culturable mycoplasmas; consequently, small genome size alone cannot explain MLO non-culturability. Hybridization with cloned MLO-specific chromosomal and 16S rRNA probes detected two separate chromosomes in some MLO ‘type’ strains. Large DNA molecules that appear to be MLO megaplasmids were also demonstrated. The ability to characterize full-length chromosomes from virtually any non-culturable prokaryote should greatly facilitate the molecular and genetic analysis of these difficult bacteria.     

Selenoprotein P associates with endothelial cells in rat tissues

 Selenoprotein P is an extracellular heparin-binding protein that has been implicated in protecting the liver against oxidant injury. Its location in liver, kidney, and brain was determined by conventional immunohistochemistry and confocal microscopy using a polyclonal antiserum. Selenoprotein P is associated with endothelial cells in the liver and is more abundant in central regions than in portal regions. It is also present in kidney glomeruli associated with capillary endothelial cells. Staining of selenoprotein P in the brain is also confined to vascular endothelial cells. The heparin-binding properties of selenoprotein P could be the basis for its binding to tissue. Its localization to the vicinity of endothelial cells is potentially relevant to its oxidant defense function. Accepted: 6 March 1997     

Isodicentric Y chromosome: cytogenetic,molecular and clinical studies and review of the literature

Dicentrics are among the most common structural abnormalities of the human Y chromosome. Predicting the phenotypic consequences of different duplications and deletions of dicentric Y chromosomes is usually complicated by varying degrees of mosaicism (45,X cell lines), which may, in some cases, remain undetected. Molecular studies in patients with dicentric Y chromosomes have been few, and only two studies have attempted to determine the presence of SRY (the putative testis-determining factor gene). We report an 18-year-old female with short stature, amenorrhea, hirsutism, hypoplastic labia minora, and clitoromegaly who has a 45,X/46,X,idic(Y)(p11.32)/47,X,idic(Y)(p11.32),idic(Y) (p11.32) karyotype. Southern analysis using Y-specific probes (Y97, 2D6, 1F5, pY3.4) and polymerase chain reaction (PCR) analysis using primers for ZFY and SRY were positive for all loci tested, indicating that almost all of the Y chromosome was present. Our findings and an extensive review of the literature emphasize the importance of molecular analyses of abnormal Y chromosomes before any general conclusions can be reached concerning the relative effects of the Y-chromosome abnormality and mosaicism on sexual differentiation.     

Meiotic chromatin diminution in a vertebrate,the holocephalan fish Hydrolagus collie (Chondrichthyes,Holocephali)

A histochemical, microdensitometric, and electron microscopic study of testes of the ratfish Hydrolagus colliei shows that an instance of the rare phenomenon of germ line chromatin diminution occurs in this vertebrate species. In primary spermatocytes at metaphase I a spherical mass of heterochromatin accumulates at one side of the metaphase plate. At anaphase I the heterochromatic mass is left in the equatorial cytoplasm and is passed into one of the two secondary spermatocytes formed during cytokinesis. As nuclear membranes are being restored, a double membrane envelope is also formed around the heterochromatic mass, which is then termed the ‘chromatin diminution body’ (CDB). At second meiotic division the CDB is included in the cytoplasm of one of the four spermatids and retained there, apparently unchanged, until mid-spermiogenesis. At that time the CDB becomes adherent to the spermatid plasma membrane and is pinched off from the spermatid by a process of apocrine exocytosis, taking a layer of spermatid plasma membrane along with it. Simultaneously this tri-membrane CDB is taken into the adjacent Sertoli cell by endocytosis, thereby acquiring a fourth membrane layer, a part of the Sertoli cell plasma membrane. The CDBs are subsequently phagocytized, possibly first fusing with dense, multilaminate bodies in the Sertoli cell cytoplasm. The CDB chromatin mass is strongly positive with the Feulgen method for DNA and the alkaline fast green method for histones. Microdensitometric analysis shows that the discarded chromatin amounts to about 10% of the diploid nuclear content and that it appears to be part of the normal diploid complement rather than DNA amplified during meiosis.     

Normal levels of zinc and sulfhydryls in morphologically abnormal populations of spermatozoa from moderately zinc-deficient rats

Zinc is required for spermatogenesis in mammals and is concentrated in the dense outer fibers of the sperm tail, where it is associated with cysteine-rich protein. To investigate the effects of marginal zinc deficiency upon dense fiber formation and upon sperm quality in general, weanling Sprague-Dawley rats were administered a commercial low-zinc diet, supplemented with phytate, for approximately 60 days, and were compared with controls fed the same diet plus 50 ppm zinc in their drinking water. The following characteristics of the zinc-deficient rats were significantly lower than in the controls: body weight, testis weight, epididymis weight, seminal vesicle weight, sperm content of the cauda epididy-midis, sperm motility, testis zinc, and hair zinc. By contrast, the levels of sperm zinc and sperm sulfhydryls were the same in the zinc-deficient and control rats. The zinc-deficient rats displayed a highly variable spectrum of sperm defects, which included decapitation, disorganized and redundant tail elements, and superfluous cytoplasm. However, abortive dense fiber development was only rarely observed. Apparently, even when availability of zinc is limited and reduced sperm production ensues, elaboration of dense fibers rich in zinc and sulfhydryls continues to be obligatory for the completion of spermiogenesis.     

Evidence that neutral spingomyelinase of cultured murine neuroblastoma cells is oriented externally on the plasma membrane

The activity of the neutral, Mg²⁺-stimulated sphingomyelinase of cultured neuroblastoma cells (N1E-115) is enriched in the plasma membrane fraction and is reduced following treatment of intact or broken cells with trypsin, α-chymotrypsin, papain, and protease. Two protease-sensitive enzymes of the cell interior (lactate dehydrogenase and NADPH-cytochrome c reductase) are not affected by protease treatment of intact cells. These results indicate that the neutral, Mg²⁺-stimulated sphingomyelinase is oriented externally on the plasma membrane of the cultured neuroblastoma cell.     

Ultrastructural and immunofluorescence studies of basal-lamina alterations during mouse-lung morphogenesis

Epithelial differentiation during lung development appears to be influenced by mesenchyme-derived instructions coupled with hormonal regulations. The basal lamina which is associated with progenitor and differentiating epithelia during mouse embryogenesis (Theiler-stages 16-28) was examined by transmission electron microscopy and indirect-immunofluorescence microscopy. During the embryonic phase of lung development, progenitor epithelia for the pulmonary acinus projected microvilli or cytoplasmic "feet" through the basal lamina, which resulted in discontinuities and a close approximation of the adjacent mesenchymal-cell processes. These changes were also associated with the transitory polarization of mesenchymal cells perpendicular to the plane of the basal lamina, which resulted in a sheet of cuboidal mesenchymal cells adjacent to the developing acinar-tubule epithelium. During the embryonic phase of lung development, these specific interstitial or mesenchymal cells stained for heparan-sulfate proteoglycans; no other cell types were immunostained. By Theiler-stage 25, the acinar-tubule epithelia had differentiated into type-II pneumonocytes which contained lamellar bodies and significant amounts of glycogen. Fibronectin, laminin, and heparan-sulfate proteoglycan were localized in the basement membranes during the embryonic, canalicular, and terminal sac phases of lung morphogenesis. A diffuse localization of fibronectin of the interstitial cell surfaces was observed. These observations indicate that major changes in the structure and composition of basal lamina occur during the embryonic and fetal phases of pulmonary-acinus epithelial-cell differentiation and the production of pulmonary surfactant. The major changes in the basal lamina may be partly mediated by mesenchyme-derived instructions for type-II epithelial-cell differentiation.     

Acoustic communication in spring peepers

Summary In the previous study (Wilczynski et al. 1984) we found that neurons in the auditory nerve of female spring peepers (Hyla crucifer) are tuned to frequencies in the male advertisement call, whereas auditory units in male peepers are mismatched in spectral sensitivity to their call. We investigated, in the present report, behavioral consequences of this sexual dimorphism in auditory sensitivity. Call amplitude, rate of call attenuation with environmental transmission, and the amplitude of ambient noise were measured and used to compute the active space of this signal for males and females. The effect of calling height upon active space was considered. Measurements of active space were compared with intermale distances within breeding choruses.Results indicate that active space of the advertisement call for females is as much as 6 times greater than that for males, and varies directly with the height above ground from which males call. Observed maximum intermale distances correspond closely to the active space of the call for this sex. This suggests that males space themselves so that the amplitude of a neighbor's calls approximates their auditory neural threshold to call frequencies. By this proximal mechanism, peepers maximize intermale distance but ensure that they remain within a chorus.Abbreviation dB SPL decibels sound pressure levelre: 20 Pa