THE GEOTROPIC REACTION OF RODLESS MICE IN LIGHT AND IN DARKNESS

"Black—short ears—kinky tail—rodless" mice, controlled by "pink eyed—dilute—brown" mice, were tested on an inclined plane in order to determine if they are photically sensitive, and, if so, to get a quantitative expression for their visual receptivity. Rodless and control animals were tested in the dark to obtain an expression for normal geotropic orientation. Light was then introduced to modify these reactions if possible. Under light, the controls failed to orient, whereas the rodless gave reactions almost identical with those in the dark. This test has failed in this experiment to suggest sight in the rodless mouse.     

GROWTH OF MAIZE SEEDLINGS AS AFFECTED BY GLUCOKININ AND INSULIN

1. Solutions of glucokinin and insulin, particularly those from which the easily dialyzable substances had been removed, increased the growth of roots and tops of young maize seedlings, as shown by comparisons with untreated seedlings grown in distilled water. 2. Strong solutions of crude glucokinin or of crude insulin repressed growth. 3. Seedlings from which the tips of the primary roots had been removed just before placing the plants in the test solutions made greater gains in both top growth and root growth than seedlings with uncut roots treated with solutions of the same strength. Control experiments showed that this difference in growth was not the result of cutting the roots, and that crude glucokinin and crude insulin contained several substances some of which were more readily absorbed by the plant than others. 4. Purification of crude glucokinin and crude insulin by dialysis showed that the residue of relatively non-dialyzable substance was the growth-promoting fraction. 5. The dialysate of crude glucokinin contained at least three types of material, one of which repressed growth. 6. Ammonium sulfate, one of the possible impurities of glucokinin, repressed the growth of seedlings but did not produce the other changes in metabolism shown by seedlings treated with dialysate of onion glucokinin. 7. The endosperm of plants treated with growth-promoting solutions of purified insulin did not lose weight as rapidly as the endosperms of untreated plants, indicating that the treated plants made their greater gains in growth by more efficient utilization of the endosperm, or as a result of greater photosynthetic activity, or by a combination of these. 8. Experiments with albino seedlings suggested that the greater gain in weight made by plants treated with insulin was the result in part of increased photosynthetic activity.     

Analysis of the Albino-Locus Region of the Mouse: IV. Characterization of 34 Deficiencies

Thirty-four independent nonviable c-locus mutations (types c^al, albino lethal and c^as, albino subvital), derived from radiation experiments, were tested for involvement of nearby markers tp, Mod-2, sh-1, and Hbb: 10, 22, and 2 involved, respectively, none of these markers, Mod-2 alone, and Mod-2 plus sh-1. When classified on this basis, as well as according to developmental stage at which homozygotes die, and by limited complementation results, the 34 independent mutations fell into 12 groups. From results of a full-scale complementation grid of all 435 possible crosses among 30 of the mutations, we were able to postulate an alignment of eight functional units by which the 12 groups fit a linear pattern. Abnormal phenotypes utilized in the complementation study were deaths at various stages of prenatal or postnatal development, body weight, and reduction or absence of various enzymes. Some of these phenotypes can be separated by complementation (e.g., there is no evidence that mitochondrial malic enzyme influences survival at any age); others cannot thus be separated (e.g., glucose-6-phosphatase deficiency and neonatal death).—We conclude that all of the nonviable albino mutations are deficiencies overlapping at c, and ranging in size from <2cM to 6-11 cM. The characterization of this array of deficiencies should provide useful tools for gene-dosage studies, recombinant-DNA fine-structure analyses, etc. Since many of the combinations of lethals produce viable albino animals that resemble the standard c/c type, we conclude (a) that the c locus contains no sites essential for survival, and (b) that viable nonalbino c-locus mutations (c^xv) are the result of mutations within the c cistron. Viable albinos (c^av, the majority of radiation-induced c-locus mutations) may be intracistronic mutations or very small deficiencies.     

The measurement of protein synthesis in biological systems

Attempts to quantitate metabolism in the lung and other tissues using radioactive precursors may be subject to significant errors arising from inappropriate assumptions regarding precursor metabolism, compartmentation and specific radioactivity. This article reviews the type and magnitude of error which may complicate such measurements by presenting specific data from experiments using radioactive amino acids to estimate the rate of protein synthesis. The applicability of these observations to other metabolic systems is discussed briefly in order to develop a more general awareness of the errors which may result from incomplete validation of experimental measurements using radioisotopes.     

The adult β-globin genes of the “single” type mouse C57BL

A set of four clones containing the two adult β-globin genes of the “single” type mouse C57BL/10 (genotype Hbb^s/Hbb^s) were isolated from a library of cloned restriction fragments. The two genes, designated βs and βt, were physically mapped onto a 32 kb segment of the chromosome carried by the four clones. βs and βt form a stable heteroduplex 1850 bp long, indicating that they are intact and conserved at this level of resolution throughout their length, including their intervening sequences. The βs gene is allelic with the βdmaj gene of the BALB/ c mouse (genotype Hbb^d/Hbb^d). These two alleles, as well as their surrounding sequences, are highly conserved. In contrast, heteroduplexes of βt with its BALB/c allele, βdmin, revealed three extensive but localized rearrangements. One region of non-homology falls within the large intervening sequence, IVS2. To the 5′ side of the βt/βdmin gene position two unequal substitutions were observed; each results in the net insertion of about 1000 bp into the Hbb^d chromosome. The β/βdmin gene position is bracketed by a 1450 bp inverted repeat. One of the 1000 bp substitutions maps within this inverted repeat.     

Ingestion of a high-glycemic index meal increases muscle glycogen storage at rest but augments its utilization during subsequent exercise.

The aim of this study was to compare the effect of preexercise breakfast containing high- and low-glycemic index (GI) carbohydrate (CHO) (2.5g CHO/kg body mass) on muscle glycogen metabolism. On two occasions, 14 days apart, seven trained men ran at 71% maximal oxygen uptake for 30 min on a treadmill. Three hours before exercise, in a randomized order, subjects consumed either isoenergetic high- (HGI) or low-GI (LGI) CHO breakfasts that provided (per 70 kg body mass) 3.43 MJ energy, 175 g CHO, 21 g protein, and 4 g fat. The incremental areas under the 3-h plasma glucose and serum insulin response curves after the HGI meal were 3.9- (P < 0.05) and 1.4-fold greater (P < 0.001), respectively, than those after the LGI meal. During the 3-h postprandial period, muscle glycogen concentration increased by 15% (P < 0.05) after the HGI meal but remained unchanged after the LGI meal. Muscle glycogen utilization during exercise was greater in the HGI (129.1 +/- 16.1 mmol/kg dry mass) compared with the LGI (87.9 +/- 15.1 mmol/kg dry mass; P < 0.01) trial. Although the LGI meal contributed less CHO to muscle glycogen synthesis in the 3-h postprandial period compared with the HGI meal, a sparing of muscle glycogen utilization during subsequent exercise was observed in the LGI trial, most likely as a result of better maintained fat oxidation.