Effect of GA3 on the Cyclic AMP Biosynthesis in Maize Seedling

The effect of GA₃ on the biosynthesis of cAMP was studied toinvestigate the mechanism of gibberellic acid action. The presenceof cAMP in germinating maize seedlings was confirmed. The concentrationgradient of cAMP in maize seedlings inclined from shoot apexto root. The amount of cAMP in maize shoot was increased about3.3 times by exogenous GA₃. These results indicate that thebiosynthesis of cAMP is stimulated by GA₃. (Received June 17, 1986; Accepted January 22, 1987)     

Radiation sensitivity of hemopoietic stroma: long-term partial recovery of hemopoietic stromal damage in mice treated during growth

We studied the ability of the hemopoietic organ stroma to recover from damage inflicted by 5 or 7 Gy gamma radiation administered during a period of stromal growth in 4-week-old mice. Irradiation resulted in an immediate depletion of femoral colony-forming fibroblastic progenitors (CFU-F) down to 10-20% of age-matched control values. A full recovery to normal numbers occurred between 120 and 240 days after irradiation and was followed by a secondary decrease 1 year after irradiation. This secondary decrease was accompanied by a decrease in the femoral CFU-S and CFU-C content. Femoral CFU-F attained normal numbers and it was demonstrated to occur from surviving CFU-F and could not be enhanced or prolonged following infusion of unirradiated bone marrow cells after irradiation. During the transient CFU-F recovery the hemopoietic stroma remained severely damaged as judged by the regenerative capacity of spleen and femur stroma after subcutaneous implantation, and the ability of the spleen to accumulate CFU-S in response to lipopolysaccharide injection. We have reported earlier that in similarly irradiated adult mice, no restoration of femoral CFU-F was observed. This difference between 4-week-old and adult mice could not be explained by a difference in in vitro radiosensitivity of CFU-F or in their in vivo regeneration kinetics following irradiation and subsequent lipopolysaccharide injection. We conclude from these observations that the recovery kinetics of the CFU-F population is different in young and adult irradiated mice, infused CFU-F do not contribute to CFU-F regeneration in an irradiated femur, CFU-F are not the sole determinants of stromal regeneration in femur and spleen following irradiation.     

Dynamics of populations with changing rates: generalization of the stable population theory

A general and complete exposition of the dynamics of populations with changing vital rates is given in the discrete time formulation. Results obtained are stronger than Lopez's or Hajnal's. In addition to the proof of existence of limits, an explicit expression for the age distribution is obtained by considering forward products of population projection matrices, while an explicit expression for the generalized reproductive values is obtained by considering backward products. The forward and backward characteristic equations respectively determine the forward and backward growth rates. The relative age distribution is compared to the alternative expression of Y.J. Kim (1986, Demography 23 (3), 451-461), which is the discrete version of S.H. Preston and A.J. Coale (1982, Pop. Index 48 (2), 217-259).     

Molecular cloning and differential expression of somatic and testis-specific H2B histone genes during rat spermatogenesis

We have cloned cDNA of a testis-specific histone, TH2B (a variant of H2B), and rat somatic H2B gene to investigate regulation of testis-specific histone genes during rat spermatogenesis. The amino acid sequences deduced from DNA sequences show extensive sequence divergence in the N-terminal third of the two histones. The rest is highly conserved. One cysteine residue was found in TH2B. No cysteine is present in somatic histones except in H3 histone. We investigated the expression of TH2B and H2B genes using the regions of sequence divergence as hybridization probes. The TH2B gene is expressed only in the testis, and the expression of this gene is detected 14 days after birth, reaching a maximum at Day 20. The level of H2B mRNA shows a reciprocal pattern. This contrasting pattern can be explained by the gradually changing proportion of spermatogonia and spermatocytes with testicular maturation. In situ cytohybridization studies show that H2B gene is expressed primarily in proliferating spermatogonia and preleptotene spermatocytes, whereas TH2B gene is expressed exclusively in pachytene spermatocytes which first appear in testis about 14 days after birth. H2B and TH2B genes appear to be ideal markers for the study of proliferation and differentiation events in spermatogenesis and their regulatory mechanisms.     

Beta B1 crystallin is an amine-donor substrate for tissue transglutaminase

The effects of tissue transglutaminase on the water-soluble proteins in bovine lens homogenates are described. Addition of liver transglutaminase and Ca2+ to calf lens homogenates resulted not only in the appearance of 50- and 57-kDa dimers, but also in a decrease in the amount of beta B1 crystallin and the almost complete disappearance of beta B3 and beta A3. This is not the result of Ca2+-induced proteolysis, since histamine completely inhibits this phenomenon. It may be concluded that these polypeptides are involved in beta-crystallin crosslinking by transglutaminase. This notion was confirmed by using beta B1- and beta Bp-specific antisera. Both sera reacted with the 57-kDa dimer; the beta Bp-specific antiserum also reacted with the 50-kDa dimer. No reaction in the region 50-57 kDa was detectable when EDTA was used instead of Ca2+. Using reconstituted mixtures of beta B1- and beta Bp-crystallin chains, and N-terminally truncated derivatives thereof, it was shown that in the beta B1/beta Bp dimer, glutamine residue -9 of beta Bp crosslinks to one of the lysine residues in the N-terminal extension of beta B1.     

The pancreatic glucagon and C-peptide secretion during hyperinsulinemia in euglycemic glucose clamp with or without somatostatin infusion in normal man

6 normal subjects received two times of 2 hr euglycemic glucose clamp studies (insulin infusion rate 40 mU/M2/min) one with and the other without somatostatin (SRIF) infusion (500 microgram/hr). Serum C-peptide and glucagon levels were measured during clamp to study the sensitivity of pancreatic alpha and beta cells to the suppressive effects of exogenous hyperinsulinemia during normoglycemia in normal subjects and to find whether SRIF had any modulative effects on endocrine pancreas secretion at the status of hyperinsulinemia. The results showed that in normal man the degree of suppression of pancreatic glucagon secretion by hyperinsulinemia (approximately 100 uU/ml) during euglycemic glucose clamp without SRIF infusion was less than that of C-peptide with mean value of 62 +/- 4% of basal glucagon remained at the end of clamp study; while only about 30 +/- 2% of basal C-peptide concentrations remained. But during SRIF infused glucose clamp studies (SRIF was infused from 60 to 120 min), 32 +/- 2% of mean basal C-peptide concentrations and 38 +/- 6% of mean basal glucagon concentrations left at the end of 2 hr clamp studies when serum insulin level was about 100 uU/ml. For the glucose infusion rate (M value), it was significantly greater in our normal subjects in response to insulin + SRIF as compared to insulin alone (12.0 + 0.9 vs 8.8 +/- 1.4; P less than 0.01). We concluded: during hyperinsulinemia (100 uU/ml), the sensitivity of pancreatic alpha cells to insulin seems less than that of beta cells in normal man at normoglycemia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Recalibration of the Pseudomonas aeruginosa Strain Pao Chromosome Map in Time Units Using High-Frequency-of-Recombination Donors

High-frequency-of-recombination donors of P. aeruginosa strain PAO were generated using a temperature-sensitive, replication mutant of the IncP-1 plasmid R68, loaded with the transposon Tn2521. Fourteen donors so isolated mobilized the chromosome in a polarized manner from a number of different transfer origins. The donors were used to construct a time of entry map of the entire chromosome and this was achieved by determining the time of entry of 32 randomly dispersed markers in crosses using nalidixic acid to interrupt chromosome transfer. Analysis of the time of entry data enabled the recalibration of the chromosome map to 75 min.     

The nifA gene of Rhizobium meliloti is oxygen regulated.

Experiments using plasmid-borne gene fusions and direct RNA measurements have revealed that expression from the nifA gene is induced in Rhizobium meliloti when the external oxygen concentration is reduced to microaerobic levels. Induction occurs in the absence of alfalfa and in the presence of fixed nitrogen and does not require ntrC. The production of functional nifA gene product (NifA) can be demonstrated by its ability to activate the nitrogenase promoter P1. Aerobic induction of nifA can also occur during nitrogen starvation at low pH, but in this case induction is dependent on ntrC and does not lead to P1 activation. The data indicate that reduced oxygen tension is potentially a major trigger for symbiotic activation of nitrogen fixation in Rhizobium species.     

Effect of growth phase on phospholipid biosynthesis in Saccharomyces cerevisiae.

The effect of growth phase on the membrane-associated phospholipid biosynthetic enzymes CDP-diacylglycerol synthase, phosphatidylserine synthase, phosphatidylinositol synthase, and the phospholipid N-methyltransferases in wild-type Saccharomyces cerevisiae was examined. Maximum activities were found in the exponential phase of cells grown in complete synthetic medium. As cells entered the stationary phase of growth, the activities of the CDP-diacylglycerol synthase, phosphatidylserine synthase, and the phospholipid N-methyltransferases decreased 2.5- to 5-fold. The subunit levels of phosphatidylserine synthase and the cytoplasmic-associated enzyme inositol-1-phosphate synthase were not significantly affected by the growth phase. When grown in medium supplemented with inositol-choline, cells in the exponential phase of growth had reduced CDP-diacylglycerol synthase, phosphatidylserine synthase, and phospholipid N-methyltransferase activities, with repressed subunit levels of phosphatidylserine synthase and inositol-1-phosphate synthase compared with cells grown without inositol-choline. Enzyme activity levels remained reduced in the stationary phase of growth of cells supplemented with inositol-choline. The phosphatidylserine synthase and inositol-1-phosphate synthase subunit levels, however, were depressed. Phosphatidylinositol synthase (activity and subunit) was not affected by growth in medium supplemented with or without inositol-choline or the growth phase of the culture. The phospholipid composition of cells in the exponential and stationary phase of growth was also examined. The phosphatidylinositol to phosphatidylserine ratio doubled in stationary-phase cells. The phosphatidylcholine to phosphatidylethanolamine ratio was not significantly affected by the growth phase of cells.