Peculiarities in the organization of testis of Ophidian sp. (Pisces Teleostei). Evidence for two types of spermatogenesis in teleost fish

The walls of lobules in the testis of Ophidion sp. are composed of Scrtoli cells and young germinal cells (spermatogonia and spermatocytes). Spermatocytes are linked by cytoplasmic bridges. The associations of Sertoli cells and spermatocytes constitute true cysts. Meiosis takes place in the cysts. When meiosis is complete, cysts open. Spermatids are released into the lumen of the lobules and the cyloplasmic bridges break down. Spermiogenesis occurs in the lumen. Spermatids at various levels of spermiogenesis are then mixed with ripe spermatozoa. In teleosts we thus recognize two types of spermatogenesis: a cystic type where spermatogenesis is completed within cysts, and leads to synchronous development of germ-cells; and a semi-cystic type, where spermatogenesis occurs partly outside cysts. This may produce asynchronous spermatogenesis.     

Demonstration of an antigenic protein specific for Salmonella typhi

Current studies were undertaken to determine the presence of a specific antigenic protein on the outer membrane of Salmonella typhi. Immunoblot analysis using sera from patients with fevers revealed that the 50 kD band was specifically recognized only by typhoid sera. The 50 kD band located on the outer membrane is protein by nature and is not a Vi (capsular), dH (flagellar), or O9 (somatic) antigen of S. typhi. These results indicate the usefulness of the specific antigen in the development of a serodiagnostic test for typhoid fever since antibodies of both the IgM and IgG class responses were obtained.     

Characterisation of mitochondrial fractions isolated from four genotypes of wheat coleoptiles

Mitochondrial fractions were isolated at various stages of germination from wheat coleoptiles of 4 different genotypes: WRH, Capitole, male-sterile Capitole (MSC) and F₁ hybrid obtained by crossing MSC with WRH. The ADP: O values were the highest in F₁ and in MSC and decreased during germination. The oxygen consumption was weaker in F₁ and in WRH than in the other genotypes. Quantitative differences in polypeptides exist between the different genotypes. On germination, increase in the polypeptides of high MW was more rapid in F₁ than in the other genotypes. The fatty acids of the mitochondria of F₁ and MSC are characterized by an abundance of linoleic acid. The content of this fatty acid decreased during germination more rapidly in F₁ and in MSC than in the others. The cytoplasm of Triticum timopheevi has a marked influence on mitochondria of MSC and F₁. This cytoplasm confers better oxidative properties, which can be correlated with changes in their biochemical constituents. However the F₁ hybrid differs from the other genotypes in many biochemical features.     

Strong convergence of integrators for nonequilibrium Langevin dynamics

Several numerical schemes are proposed for the solution of Nonequilibrium Langevin Dynamics (NELD), and the strong rate of convergence for each scheme is analyzed. The schemes considered here employ specialised periodic boundary conditions that deform with the flow, namely Lees-Edwards and Kraynik-Reinelt boundary conditions and their generalisations. We show that care must be taken when implementing standard stochastic integration schemes with these boundary conditions in order to avoid a breakdown in the strong order of convergence.     

Role of the stringent response in the expression and mechanism of near-ultraviolet induced growth delay

The near-ultraviolet (300-400 nm) induced growth delay of Escherichia coli cells was compared in isogenic relA+ and relA- cells illuminated either in the stationary or the exponential phase. In the latter case: (a) the relA- strains of K12 and B/r exhibited similar maximal growth lags (65 min and 55 min respectively); (b) the maximal lags were 1.5-fold and 4-fold longer, respectively, in the isogenic relA+ strains; (c) the rate of the relA- -dependent guanosine 3',5'-bis(diphosphate) (ppGpp) accumulation was three-times lower in the K12 relA+ strain as compared to the B/r relA- strain: (d) a K12 spoT mutant having an impaired rate of ppGpp degradation had a 2-fold longer lag. On the other hand, when illumination is performed in the stationary phase, isogenic relA+ and relA- cells (B/r or K12) exhibited similar growth lags at any fluences, indicating little if any involvement of the stringent response. These data extend previous observations of T.V. Ramabhadran an J. Jagger [(1976) Proc. Natl Acad. Sci. USA, 73, 59-63] but do not support their conclusion that the stringent response is the main factor responsible for growth delay. By monitoring the intracellular level of ppGpp in relA+ spoT- and relA+ spoT+ growing cells during illumination and the subsequent growth lag we observed that the initial burst of ppGpp decreases slowly all along the lag; in all relA+ strains checked the return of ppGpp to its basal level coincides with the recovery of normal growth. We conclude that it is the accumulation of ppGpp over the basal level due either to the stringent response or to prevention of ppGpp degradation that is responsible for an amplification of the growth lag.     

Ending AIDS as a public health threat by 2030: Time to reset targets for 2025

Paul De Lay and co-authors introduce a Collection on the design of targets for ending the AIDS epidemic.     

Use of a Fluorimetric Method to Assay the Binding and Transfer of Phospholipids by Lipid Transfer Proteins from Maize Seedlings and Arabidopsis Leaves

A fluorimetric method has been used to study the binding andtransfer of phospholipids mediated by a lipid transfer protein(LTP) from maize seedlings and by proteins extracted from Arabidopsisleaves. This method is based on the use of donor vesicles preparedby sonication or injection and consisting of either self quenchingvesicles of (1-palmitoyl 2-{12-{(7-nitrobenzoxadiazol-4-yl)amino}dodecanoyl}-Sn-glycero-3-phosphocholine(NBD-PC) or trinitrophenylphosphate phosphatidyl ethanolamine(TNP-PE) quenched vesicles of l-palmitoyl-2(l-pyredecanoyl)-Snglycero-3-phosphocholine(Pyr-PC). Acceptor vesicles consisted in a mixture (90/10; v/v)of dioleoylphosphatidylcholine and phosphatidyl inositol (DOPC-PI).The use of injected vesicles of Pyr-PC allowed to achieve sensitiveand qualitative tests of binding and transfer since 0.05 µMLTP were detected. By contrast, when sonicated vesicles of NBD-PCwere used, quantitative determinations of phospholipid-LTP complexas well as measurement of the initial rate of phospholipid transferon a large range of protein concentration (0.5 to 20 µM)were performed. This fluorimetric method has been successfullyused to study the activity of maize LTP during its purificationor the activity of LTPs present in Arabidopsis extracts. (Received December 5, 1993; Accepted December 7, 1993)