Molecular cloning and chromosome mapping of a mouse DNA sequence homologous to homeotic genes of Drosophila

Some of the homeotic genes of Drosophila, involved in the control of segmental development, form a diverged multigene family. A conserved DNA sequence common to these genes has been used to isolate a clone (Mo-10) from the mouse genome which contains a sequence coding for a protein domain that is homologous to the domain conserved in the Drosophila homeotic genes. By structural analogy, this sequence may be involved in the control of metameric pattern formation in the mouse. Mo-10 has been mapped to the proximal portion of mouse chromosome 6, and its position in relationship to genes known to influence mouse morphogenesis is discussed.     

Is There a Role for the Apex in Shoot Geotropism?

Experiments with horizontal etiolated sunflower (Helianthus annuus L.) seedlings supported centrally such that both apical and basal ends are free to react to geostimulus, revealed that the apical end commences curvature 1 to 2 hours earlier than the basal end. The later curvature in the basal region is a consequence of the absence of growth in the initial period rather than merely slower growth. A comparison of zonal growth rates in a vertical and a horizontal seedling confirmed that geostimulus induces a renewal of growth in a region where growth had ceased. Removing the apical half of the hypocotyl showed that the curvature resulting from this growth initiation in the basal region is dependent on attachment to the apical region. Evidence that this dependence is unlikely to be due to energy deficiency is adduced. The prior response of the apical end to geostimulus and the apically dependent later initiation of new growth in the basal region are compatible with the delay inherent in message transport from apex to base and are considered as evidence for apical involvement in the totality of the seedling's georesponse.     

Auditory sensitivity and psychophysical tuning curves in the elephant nose fish,Gnathonemus petersii

Summary Hearing sensitivity and psychophysical tuning curves were determined for the mormyridGnathonemus petersii. Pure tone hearing thresholds were determined from 100 Hz to 2,500 Hz, with best sensitivity being about –31 dB (re: 1 dyne/ cm²) from 300 Hz to 1,000 Hz. In order to determine frequency tuning of the auditory system, psychophysical tuning curves (PTC's) were measured with the masker presented simultaneously with, or just ahead of, the 500 Hz test signal. The sound level for different frequencies needed to just mask the test tone were determined from 100 to 800 Hz. Maximum masking occurred in both forward and simultaneous conditions when the masker and the test tone were at the same frequency. As the masker was moved in frequency from 500 Hz, higher sound levels of maskers were needed to afford masking of the test tone. The data were similar in simultaneous and forward masking, with theQ _{10 dB}, a measure of sharpness of tuning, being about 5 in both cases. Data were compared for other species for which behavioral thresholds and PTC's are available.Gnathonemus hears about as wide a range of frequencies as the goldfish,Carassius auratus, although the PTC's for the two species are strikingly different. The PTC's forGnathonemus resemble those determined in a forward-masking paradigm for the clown knife fish,Notopterus chitala, even thoughGnathonemus has a wider hearing bandwidth.Abbreviations AM amplitude modulated - EOD electric organ discharge - PTC psychophysical tuning curve     

Absence of generalized immunosuppression in C57BL/6J mice implanted with Lewis T241 fibrosarcoma or Lewis lung carcinoma

Summary The immune status of C57BL/6J mice implanted with Lewis T241 fibrosarcoma or Lewis lung (LL) carcinoma was investigated on days 14 and 28 after implantation. Splenic lymphocyte responses were assessed in mitogen (Con A, LPS) mixed lymphocyte culture (MLC), natural killer (NK), graft-vs-host (GVH), and interleukin production assays. Except for NK-cell cytotoxicity, all other immunologic parameters were either comparable to those in medium-implanted controls or augmented. NK cytotoxicity was reduced in both tumor-bearing groups on day 28. The provision of NK potentiation therapy (-interferon, polyinosinic: polycytidylic acid) to T241 mice under various treatment conditions did not have any significant effect on lung metastasis or survival.The results of this study do not support the thesis that T241-or LL-bearing C57BL/6J mice are generally immunosuppressed. Indeed, when immune functions were assessed on the basis of total splenic activity, each of the measured immunologic parameters was substantially greater in animals with tumors than without. Further it seems improbable, considering the magnitude of the NK-cell defect in T241 mice on days 14 and 28 after implantation and the absence of a therapeutic response to NK-cell stimulants, that NK-cell cytotoxicity is intrinsically associated with resistance to tumor progression in this model.     

Studies in vitro of the nature and synthesis of the cell wall ofChlamydia trachomatis

The possibility thatChlamydia trachomatis contains peptidoglycan was examined by three methods. Preincubation of chlamydia with enzymes known to cleave peptidoglycan had no adverse effect on the subsequent development. Immunofluorescence studies with antistreptococcal peptidoglycan antisera failed to show any cross reactions with chlamydial antigens. The antichlamydial activity of anti-cell-wall antimicrobials was examined; lactams proved the most active, and cycloserine and bacitracin also showed antichlamydial activity. Alaphosphin, phosphomycin, and vancomycin showed no antichlamydial activity at the concentrations tested.     

Functional morphology of the branchial basket of ascidia paratropa (Tunicata,Ascidiacea)

Summary The filtering surface of the branchial basket of Ascidia paratropa (Huntsman, 1912) consists of two adjacent and connected sheets. The stigmatal surface is loosely folded. The secondary gill screen, composed of ciliated longitudinal vessels with primary and secondary papillae, is connected to the stigmatal surface on the inside of the branchial basket. Continuous mucus secretion results in a net with elastic and adhesive properties, and a pore size of less than 0.5 m in its longest dimension. Net production cannot be interrupted by external mechanical stimuli. The net is usually supported by and transported across the secondary screen, forming a filtering surface that parallels the undulations of the stigmatal surface; however, localized muscular activity of the dorsal laminar fold and longitudinal vessels are also involved in mucous net transport. Squirts occur more frequently than in many species. At these times the net is transported as a flat sheet, independent of the secondary screen. Squiring does not interrupt continuous feeding activity.     

Different Sensitivities of Granulocyte-Macrophage and Erythroid Progenitor Cells of Normal Human Bone Marrow to S-Phase-Specific Agents

The extraordinary sensitivity of early erythroid progenitor cells (BFU-e) of normal human bone marrow to tritiated thymidine ([³H]TdR) was studied. While exposure of bone-marrow cells to [³H]TdR for 1 hr resulted in the death of only 40% of the granulocyte-macrophage progenitor cells (CFU-c), 90% of BFU-e were killed. Experiments in which normal bone-marrow cells were mixed with bone-marrow cells which had been exposed to [³H]TdR demonstrated that the excessive killing of BFU-e by [³H]TdR reflected carry-over of the [³H]TdR by the exposed cells. A carry-over effect was not observed for CFU-c, suggesting the presence of a fundamental difference in the metabolism of TdR between CFU-c and BFU-e. There was a suggestion of a carry-over effect regarding two other S-phase-specific agents, hydroxyurea and 1-β-D-arabinofuranosylcytosine.     

Sodium-23 NMR studies of cation-DNA interactions

Sodium-23 NMR has been used to study the extent to which monovalent cations associate with double stranded DNA in aqueous solution (28°C, pH = 7.5). On the basis of the two site model for rapid exchange the ²³Na linewidth can be related to the fraction of sodium ions associated with DNA. To test the applicability to this system of the condensation model for the association of small counterions with polyelectrolytes, the concentration dependence of the sodium linewidth has been determined by making additions of NaCl to solutions of tetraethyl or tetrabutylammonium DNA. ([P], the DNA phosphate concentration was about 0.02M). The resulting titration curves extend over a wide range of the ratio [Na]/[P] (0.3–30). When [Na]/[P] ? 3 only sodium is associated, and the extent to which it compensates the charges on DNA does not vary with the addition of salt, at least until [Na]/[P] ≈ 30, the highest concentration examined. When [Na]/[P] ? 3 the tetraalkylammonium species is also associated with DNA; an equation has been derived to account for the effect on the ²³Na linewidth of the competition between sodium and another monovalent cation. Based on the assumption that the fraction of uncompensated charge remaining on DNA after the condensation of both species is constant, this equation fits all the linewidth data if the charge fraction is in the range 0.25 ± 0.10. The value required by the condensation model for DNA in the presence of monovalent counterions is ξ^?1 = 0.24. The reasonable agreement between experimental and theoretical values of the charge fraction and its invariance with respect to large variations in the concentration of added salt indicate that even in moderately concentrated solutions of DNA, the association of sodium can usefully be described in terms of the condensation model. If the theoretical value of the charge fraction is assumed, it follows from fitting the titration curves that the approximate relative affinities for DNA of Na⁺, Et₄N⁺, and Bu₄N⁺ are in the ratio 20:5:1, and the transverse relaxation rate of condensed sodium is 180 ± 10 s^?1.     

Decreased sialyltransferase activity in the hearts of cardiomyopathic hamsters

Sialyltransferase activity was compared in homogenates and microsomal fractions from hearts of cardiomyopathic Syrian hamsters and age-matched normal controls. Decreased enzymatic activity was found in cardiomyopathic hamsters, with most of the decline occurring between the first and second month of life; it was associated with a parallel fall in mcirosomal sialic acid content. Since membrane-bound sialic acid may control Ca²⁺ exchangeability in cardiac muscle (and, indirectly, tension development), these results provide a biochemical basis for the development of cardiac failure in the Syrian hamster.