CHROMOSOMAL DIFFERENTIATION IN CLARKIA DUDLEYANA

Snow , Richard . (U. California, Davis.) Chromosomal differentiation in Clarkia dudleyana. Amer. Jour. Bot. 47 (4) : 302—309. Illus. 1960.—Clarkia dudleyana (n=9) is a common, colonial annual of the early-summer California flora. Of 275 individuals, derived from 9 natural populations and their garden-grown representatives, 17.1% were heterozygous for reciprocal translocations. Supernumerary chromosomes were also found in about 2% of the plants examined. The translocation heterozygotes are not distributed regularly over the species range but are concentrated near the geographical center of distribution. Most of the populations contained none or only a few heterozygotes, but in one colony 69% of 42 plants sampled were heterozygous. Judging from the meiotic metaphase associations observed, at least 5 different chromosome arrangements are present at this locality. Hybrids between colonies have invariably been translocation heterozygotes, the largest association found in such hybrids being a chain of all 18 chromosomes (a potential ring of 18). No correlation is evident between geographical separation and degree of cytological differentiation. Heterozygotes with smaller rings of 4 or 6 chromosomes, whether from natural populations or resulting from interpopulation hybridization, are highly fertile owing to the regular alternate disjunction of the chromosomes of the rings. In the larger rings of 12 to 18 chromosomes, derived from interpopulation crosses, segregation is much more irregular and leads to high sterility. It is possible that at least in some localities the heterozygotes enjoy a selective advantage over their homozygous sibs. It is also postulated that homozygosity for a particular chromosome arrangement may be selectively favored in a certain habitat, as a result of a position effect attendant upon placing formerly non-linked genes in the same linkage group through reciprocal translocation. The high degree of chromosomal differentiation between some populations of this species suggests that the complex heterozygotes of Oenothera have arisen as a result of hybridization of cytologically differentiated races.     

Hypoxanthine phosphoribosyltransferase activity in tissues and hypoxanthine concentrations in plasma and CSF of the horse in comparison with other species

1. Plasma hypoxanthine and xanthine concentrations are very low in the horse and low in rat, mouse and greyhound compared to concentrations in beagles, man, sheep and rabbit. 2. Activities in erythrocytes of the main enzyme metabolizing hypoxanthine, hypoxanthine phosphori-bosyltransferase, show a similar pattern (Tax et al., 1976, Comp. Biochem. Physiol. 54B, 209-212); thus low activities have been found where plasma concentrations were low. 3. Hypoxanthine phosphoribosyltransferase activities in horse tissue other than erythrocytes are similar to those in man and rabbit with high activities in brain; this enzyme may therefore be functionally important in equine brain.     

Drosophila neuroglian: a member of the immunoglobulin superfamily with extensive homology to the vertebrate neural adhesion molecule L1

Drosophila neuroglian is an integral membrane glycoprotein that is expressed on a variety of cell types in the Drosophila embryo, including expression on a large subset of glial and neuronal cell bodies in the central and peripheral nervous systems and on the fasciculating axons that extend along them. Neuroglian cDNA clones were isolated by expression cloning. cDNA sequence analysis reveals that neuroglian is a member of the immunoglobulin superfamily. The extracellular portion of the protein consists of six immunoglobulin C2-type domains followed by five fibronectin type III domains. Neuroglian is closely related to the immunoglobulin-like vertebrate neural adhesion molecules and, among them, shows most extensive homology to mouse L1. Its homology to L1 and its embryonic localization suggest that neuroglian may play a role in neural and glial cell adhesion in the developing Drosophila embryo. We report here on the identification of a lethal mutation in the neuroglian gene.     

Evaluation of a system for the imposition of plant water stress

A system which imposes a range of water stress levels was developed and evaluated. Water stress was controlled by employing a screen to suspend roots above a water column of known height. Levels of water stress were imposed by changing water column height and/or hydraulic conductivity of the medium in the column. The system was evaluated in a series of growth chamber experiments in which sunflowers (Helianthus annuus L. cv NK894) were given three levels of water availability for a period of 3 weeks. Third leaf midday water potentials at the end of the trials ranged from −0.73 ± 0.04 to −2.35 ± 0.17 megapascals in waterstressed plants compared to −0.40 ± 0.02 megapascals for control plants. Repetition of experiments showed no statistical differences in leaf water potentials, plant leaf areas, or plastochron indices between trials. During the experiments, the severity and pattern of water stress developments was related to both water column height and conductivity of the medium. Control plants exhibited normal diurnal water relations and transpirational behavior. Use of this system avoids many problems associated with other techniques and provides a means for subjecting plants to reproducible water stress levels for extended periods of time.     

The inheritance of skeletal muscle fibre composition in mice

Two inbred strains of mice C3H/HE and SWR, and generations produced by intercrossing, were studied to investigate the effect of heredity on muscle composition. The data were found to be consistent with a polygenic mode of inheritance. No simple effect of sex-linkage or maternal influence was evident. The heritability of fibre type percentage total fibre number and the relative size of Type I and Type II fibres were highly significant. Principal component analysis yielded a "genetic" vector which accounted for 57% of the variation in muscle fibre composition. Patterns of covariance of fibre type percentage, total fibre number and relative sizes of Type I and Type II fibres showed a single correlated response.     

Metabolic response of equine muscle to intermittent maximal exercise

Four thoroughbred horses performed 4 gallops (G1-G4) with intervals of 5 min. With one exception, gallops were sustained at maximal speed over 620 m. Muscle biopsy samples of the middle gluteal and brachiocephalicus were taken before, during, and after exercise and assayed for ATP and intermediary metabolites. The results showed a major involvement of the brachiocephalicus, in addition to the middle gluteal, during galloping. In three horses, who were clearly fatigued, muscle ATP decreased by up to 50% by the end of G4. This was matched by an equal rise in inosine 5'-monophosphate. Pronounced accumulations of glycerol 3-phosphate, glycerol, and lactate (up to 204 mmol X kg dry muscle-1) occurred with exercise. In the fourth horse, which was less fatigued, a decrease in ATP and increases in intermediary metabolites were much less. Postexercise there was little or no recovery in muscle ATP or lactate during 30 min. The decreases in ATP are consistent with a high activity of adenosine 5'-monophosphate deaminase in horse muscle and indicative also of the high level of anaerobic stress of the exercise program. There was evidence to suggest that the increase in muscle glycerol resulted from hydrolysis of glycerol 3-phosphate and not from the utilization of triglyceride.     

Kinetics of incorporation of O6-methyldeoxyguanosine monophosphate during in vitro DNA synthesis

O6-Methyldeoxyguanosine triphosphate (m6dGTP), known to be produced in vivo by methylation of deoxyguanosine triphosphate with simple methylating mutagens, is utilized by prokaryotic DNA polymerases during in vitro replication of synthetic and natural DNA template-primers. A study of the kinetic behavior of m6dGTP during DNA replication in vitro and of its effect on DNA replication indicates that m6dGTP acts as an analogue of dATP with Kappm of about 6 microM for Escherichia coli DNA polymerase I (Klenow fragment) compared to the Kappm of about 0.8 microM for dATP. m6dGTP is not incorporated in the complete absence of dATP (a competitive inhibitor). m6dGTP also inhibits in vitro DNA synthesis. Different DNA polymerases behave differently in utilization and turnover of m6dGTP. T4 DNA polymerase shows stronger discrimination against m6dGMP incorporation than either T5 DNA polymerase or E. coli DNA polymerase I. The possibility that m6dGTP is unlikely to contribute significantly to in vivo mutation is discussed.     

Activation of antigen-enriched B cells. II. Role of linked recognition in B cell proliferation to thymus-dependent antigens

The responsiveness to T-dependent (TD) and T-independent (TI) TNP-antigens of murine splenic B cells previously enriched for antigen-binding cells (ABC) was examined. TNP-TI antigens induced B cell proliferation. TNP-TD antigens did not induce a proliferative response regardless of the physical form or nature of the TNP-TD antigen (e.g., soluble vs particulate, low or high haptenation of carrier, TNP on various insoluble matrices, etc.). TNP-TD antigens were effective in enhancing the response of the TNP-ABC to all concentrations of lipopolysaccharide (LPS) tested, indicating that binding of antigen to surface immunoglobulin alters the LPS responsiveness of the cell. Irradiated, keyhole limpet hemocyanin- (KLH) primed T cells induced a threefold to fourfold greater B cell proliferative response with TNP-KLH than with fluoresceinated KLH (FLU-KLH) or FLU-KLH together with TNP-human serum albumin (TNP-HSA). Therefore, linked recognition appears essential for optimal T cell-mediated B cell proliferation, whereas the induction of B cell proliferation via nonlinked, carrier-activated T cells is a minor component of the response.