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At least 109 records · Page 6Linked to original sources
PubMed1981

Localization of sulfatoxygalactosylacylalkylglycerol at the surface of rat testicular germinal cells by immunocytochemical techniques: pH dependence of a nonimmunological reaction between immunoglobulin and germinal cells.

The synthesis of sulfatoxygalactosylacylalkylglycerol (SGG) is a marker of germinal cell differentiation during spermatogenesis. Antibodies raised against this lipid have been used to visualize SGG on the surfaces of rat spermatocytes and spermatids. An ionic interaction between SGG and immunoglobulin was shown to occur at physiological pH, resulting in high fluorescence backgrounds for control cells treated with nonimmune sera. Immunofluorescence was therefore performed at alkaline pH such that this interaction was much reduced or eliminated. A method was also developed to detect surface-bound complement fixed in the presence of anti-SGG. SGG was found to be mobile within the plane of the membrane, undergoing ligand-induced "patching" and occasional "capping." However, this phenomenon was independent of temperature.

Animals↗
PubMed1975

Photocontrol of the Germination of Onoclea Spores: IV. Metabolic Changes during Germination.

The changes in levels of metabolites during photoinduced germination of Onoclea sensibilis L. spores are described. Proteins and lipids, which constitute 25 and 20%, respectively, of the unimbibed spores on a dry weight basis, are hydrolyzed at the time of differentiation and elongation of the germling cells and may be utilized for these processes. Sucrose degradation, starch synthesis, and active respiration occur during dark imbibition, but these processes are accelerated by red or far red irradiation. Endogenous sucrose is the probable source of the carbon skeleton for starch synthesis.

Journal Article↗
PubMed1990

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.) : V. Water Relations of Imbibition and Germination.

The initiation of radicle growth during seed germination may be driven by solute accumulation and increased turgor pressure, by cell wall relaxation, or by weakening of tissues surrounding the embryo. To investigate these possibilities, imbibition kinetics, water contents, and water (Psi) and solute (psi(s)) potentials of intact muskmelon (Cucumis melo L.) seeds, decoated seeds (testa removed, but a thin perisperm/endosperm envelope remains around the embryo), and isolated cotyledons and embryonic axes were measured. Cotyledons and embryonic axes excised and imbibed as isolated tissues attained water contents 25 and 50% greater, respectively, than the same tissues hydrated within intact seeds. The effect of the testa and perisperm on embryo water content was due to mechanical restriction of embryo swelling and not to impermeability to water. The Psi and psi(s) of embryo tissues were measured by psychrometry after excision from imbibed intact seeds. For intact or decoated seeds and excised cotyledons, Psi values were >-0.2 MPa just prior to radicle emergence. The Psi of excised embryonic axes, however, averaged only -0.6 MPa over the same period. The embryonic axis apparently is mechanically constrained within the testa/perisperm, increasing its total pressure potential until axis Psi is in equilibrium with cotyledon Psi, but reducing its water content and resulting in a low Psi when the constraint is removed. There was no evidence of decreasing psi(s) or increasing turgor pressure (Psi-psi(s)) prior to radicle growth for either intact seeds or excised tissues. Given the low relative water content of the axes within intact seeds, cell wall relaxation would be ineffective in creating a Psi gradient for water uptake. Rather, axis growth may be initiated by weakening of the perisperm, thus releasing the external pressure and creating a Psi gradient for water uptake into the axis. The perisperm envelope contains a cap of small, thin-walled endosperm cells adjacent to the radicle tip. We hypothesize that weakening or separation of cells in this region could initiate radicle expansion.

Journal Article↗
PubMed2006

Transcription of the Bacillus subtilis gerK operon, which encodes a spore germinant receptor, and comparison with that of operons encoding other germinant receptors.

The gerA, gerB, and gerK operons, which encode germinant receptors in spores of Bacillus subtilis, were transcribed only in sporulation, and their mRNA levels peaked initially approximately 3 h before the initiation of accumulation of the spore's dipicolinic acid. After a rapid fall, levels of these mRNAs peaked again approximately 5 h later. In one wild-type strain (PS832), gerA mRNA was the most abundant, with levels of gerB and gerK mRNAs approximately 50% of that of gerA mRNA, whereas gerB mRNA was the most abundant in another wild-type strain (PY79). The synthesis of gerK mRNA in sporulation was abolished by loss of the forespore-specific RNA polymerase sigma factor, sigma(G), and induction of sigma(G) synthesis in vegetative cells led to synthesis of gerK mRNA. SpoVT, a regulator of sigma(G)-dependent gene expression, repressed gerK expression. The gerK promoter showed sequence similarities to sigma(G)-dependent promoters, and deletion of elements of this putative promoter abolished gerK expression in sporulation.

Bacillus subtilis↗
PubMed1969

Biochemical studies of bacterial sporulation and germination. XV. Fatty acids in growth, sporulation, and germination of Bacillus megaterium.

The levels of fatty acids and their distribution were determined in cultures of Bacillus megaterium during growth, sporulation, and germination. Branched-chain pentadecanoates (br-C15) were the principal fatty acids of log-phase cells. Synthesis of branched-chain tetradecanoates (br-C14) during sporulation increased the relative proportion of these branched fatty acids in sporulating cells and in mature spores. The log-phase distribution was reestablished during outgrowth of the spore. The ratio of br-C15 to br-C14 could be radically altered by addition of their respective amino acid precursors, isoleucine and valine, without seriously affecting the sporulation process. The fatty acid composition of each of the purified phospholipids from log-phase cells was the same, indicating that each phospholipid receives a portion of the fatty acid pool present in the cell at the time of its synthesis. Similarly, the fatty acids of each of the spore phospholipids resembled those of the spore extract. Phospholipids accounted for two-thirds of the fatty acids of the log-phase but only one-third of those of the spore.

Bacillus megaterium↗
PubMed1999

Molecular analysis of single B cells from T-cell-rich B-cell lymphoma shows the derivation of the tumor cells from mutating germinal center B cells and exemplifies means by which immunoglobulin genes are modified in germinal center B cells.

T-cell-rich B-cell lymphoma (TCRBCL) belongs to the group of diffuse large cell lymphomas (DLL). It is characterized by a small number of tumor B cells among a major population of nonmalignant polyclonal T cells. To identify the developmental stage of the tumor progenitor cells, we micromanipulated the putative neoplastic large CD20(+) cells from TCRBCLs and amplified and sequenced immunoglobulin (Ig) V gene rearrangements from individual cells. In six cases, clonal Ig heavy, as well as light chain, gene rearrangements were amplified from the isolated B cells. All six cases harbored somatically mutated V gene rearrangements with an average mutation frequency of 15.5% for heavy (VH) and 5.9% for light (VL) chains and intraclonal diversity based on somatic mutation. These findings identify germinal center (GC) B cells as the precursors of the transformed B cells in TCRBCL. The study also exemplifies various means how Ig gene rearrangements can be modified by GC B cells or their malignant counterparts in TCRBCL: In one case, the tumor precursor may have switched from kappa to lambda light chain expression after acquiring a crippling mutation within the initially functional kappa light chain gene. In another case, the tumor cells harbor two in-frame VH gene rearrangements, one of which was rendered nonfunctional by somatic mutation. Either the tumor cell precursor entered the GC with two potentially functional in-frame rearrangements or the second VHDHJH rearrangement occurred in the GC after the initial in-frame rearrangement was inactivated by somatic mutation. Finally, in each of the six cases, at least one cell contained two (or more) copies of a clonal Ig gene rearrangement with sequence variations between these copies. The presence of sequence variants for V region genes within single B cells has so far not been observed in any other normal or transformed B lymphocyte. Fluorescence in situ hybridization (FISH) points to a generalized polyploidy of the tumor cells.

Adult↗
PubMed1991

Microvasculature in germinal matrix layer: its relationship to germinal matrix hemorrhage.

Microvasculature in the germinal matrix layer (GML) was studied by postmortem microangiography and stereomicroscopic observation on cleared specimens in methyl salicylate. A number of arterioles from penetrating and medullary branches of main cerebral arteries were distributed in the GML, forming a fine network of arterioles anastomosing with each other. Many venules in the GML converged at a few points and drained into subependymal veins. The main converging zone of venules was situated inside the GML close to the border zone of the GML and adjacent cerebral parenchyma. The converging zone coincided with the site of GML hemorrhage. Thus, many factors, including both venous and arterial, appear to influence circulation in the GML; ultimately the converging zones become overloaded and rupture, leading to GML hemorrhage.

Angiography↗
PubMed1995

Cellular interaction in germinal centers. Roles of CD40 ligand and B7-2 in established germinal centers.

Costimulatory interactions between T and B lymphocytes are crucial for T cell activation and B cell proliferation and differentiation. We have compared the roles of CD40L and B7-2 in the initiation and maturation of humoral immunity by administering anti-CD40 ligand (L) or anti-B7-2 Ab during the early (days -1 to 3) or late (days 6-10) phases of primary responses to thymus-dependent (Td) and -independent (Ti) Ags. Germinal center (GC) formation in response to a Td Ag was inhibited completely by the early administration of anti-CD40L or anti-B7-2 Abs. Later in the response, established GCs remained sensitive to anti-CD40L but were resistant to treatment with anti-B7-2. However, Ig hypermutation was reduced dramatically in GCs of anti-B7-2-treated mice and humoral memory was impaired. Early administration of anti-CD40L reduced serum Ab levels to approximately 10% of controls, whereas early treatment with anti-B7-2 reduced Ab production by only 50%. Later treatments with either Ab had no effect on Ab production. Response to a type II Ti Ag was more resistant than Td responses to interruption of costimulatory interactions. Our findings suggest that the costimulatory roles of CD40:CD40L and B7-2:CD28/CTLA-4 differ in the GC; administration of anti-CD40L abrogates an established GC reaction, whereas Ab to B7-2 suppresses Ig hypermutation and entry into the B cell memory compartment. Once B cells have entered the differentiation pathway to Ab production, neither CD40L nor B7-2 is necessary for their continued differentiation and persistence.

Animals↗