A genetic map of mouse chromosome 1 near the Lsh-Ity-Bcg disease resistance locus

Isozyme and restriction fragment length polymorphism (RFLP) analyses of backcross progeny, recombinant inbred strains, and congenic strains of mice positioned eight genetic markers with respect to the Lsh-Ity-Bcg disease resistance locus. Allelic isoforms of Idh-1 and Pep-3 and RFLPs detected by Southern hybridization for Myl-1, Cryg, Vil, Achrg, bcl-2, and Ren-1,2, between BALB/cAnPt and DBA/2NPt mice, were utilized to examine the cosegregation of these markers with the Lsh-Ity-Bcg resistance phenotype in 103 backcross progeny. An additional 47 backcross progeny from a cross between C57BL/10ScSn and B10.L-Lshr/s mice were examined for the cosegregation of Myl-1 and Vil RFLPs with Lsh phenotypic differences. Similarly, BXD recombinant inbred strains were typed for RFLPs upon hybridization with Vil and Achrg. Recombination frequencies generated in the different test systems were statistically similar, and villin (Vil) was identified as the molecular marker closest (1.7 +/- 0.8 cM) to the Lsh-Ity-Bcg locus. Two other DNA sequences, nebulin (Neb) and an anonymous DNA fragment (D2S3), which map to a region of human chromosome 2q that is homologous to proximal mouse chromosome 1, were not closely linked to the Lsh-Ity-Bcg locus. This multipoint linkage analysis of chromosome 1 surrounding the Lsh-Ity-Bcg locus provides a basis for the eventual isolation of the disease gene.     

Facilitated diffusion of CO2 across albumin solutions

The steady-state CO₂ flux across thin layers of 30 g/100 ml albumin solutions was measured in two different CO₂ partial pressure ranges (boundary PCO ₂ values 3 and 8 torr, and 160 and 650 torr, respectively). From the data the apparent diffusion coefficient for CO₂, DCO ₂, was calculated. In the high PCO ₂ range a value of DCO ₂ was found which is to be expected on the basis of diffusion of dissolved CO₂ only. In the low PCO ₂ range DCO ₂ was about 100% higher than in the high PCO ₂ range, when carbonic anhydrase was present and the pH was ∼7.7. DCO ₂ depended on the concentration of carbonic anhydrase. It increased with increasing pH. It is concluded that an additional diffusion of bound CO₂ (facilitated CO₂ diffusion) occurs in the low PCO ₂ range and that this transport involves the hydration of CO₂. From the diffusion coefficients in the two PCO ₂ ranges the rate of facilitated diffusion was determined. Approximate calculations show that this rate (at pH ≤ 7.7) can be explained on the basis of the proposed mechanism of facilitated CO₂ diffusion: bicarbonate diffusion and simultaneous proton transport by albumin diffusion. The view that facilitated CO₂ diffusion is mediated by the diffusion of albumin is supported by the experimental finding of a considerable suppression of the facilitated CO₂ flux in the presence of gelatinized agar-agar.     

Chromosome-mediated gene transfer of multidrug resistance.

Multidrug resistance can be transferred from drug-resistant LZ Chinese hamster cells to drug-susceptible mouse LTA cells by chromosome-mediated gene transfer. Analysis of genomic DNA demonstrated the transfer of multiple copies of a DNA domain which is amplified in the donor multidrug-resistant cells. The transfer of 10 to 15 copies of the Chinese hamster gene was sufficient to produce a multidrug-resistant phenotype. Chromosome transferents exhibited overexpression of an mRNA of approximately 5 kilobases which has previously been demonstrated to be encoded by the amplified DNA domain of the donor LZ cells. Phenotypic analysis of individual clones selected in adriamycin showed the resistance to be pleiotropic. All clones tested demonstrated similar levels of cross-resistance to the drugs daunorubicin and colchicine. These results indicate that the DNA sequences transferred confer the complete multidrug-resistant phenotype on recipient cells and suggest that multidrug resistance is due to overexpression of the protein encoded by the 5-kilobase mRNA.     

Coexpression of myogenic functions in L6 rat × T984 mouse myoblast hybrids

L6 rat myoblasts differ from T984 mouse myoblasts in the expression of several myogenic functions. Simple hybrids between these myogenic lines contained mostly chromosomes and expressed the mouse phenotype. Hybrids containing an approximately balanced set of chromosomes from each parent were constructed by fusing tetraploid L6 cells to T984 myoblasts. These hybrids were allowed to differentiate and their expression of myogenic proteins was compared to the parental phenotypes. The synthesis of creatine phosphokinase isoenzymes is codominantly expressed in the hybrid cells. Myosin light chain synthesis and the levels of acetylcholine receptor are either regulated by the mouse genome or are codominantly expressed.     

The caveolae in rabbit sinus node and atrium

Summary Caveolae or membrane vesicles are commonly observed in smooth and skeletal muscle as well as in working heart muscle. Using sections of fixed tissue and replicas of freeze-cleaved material, we show in this study that caveolae are also very numerous in sinus node cells of the rabbit, and to a lesser degree, in the atrial cells.Caveolae increase the plasma membrane surface area by 115% in the leading sinus node, and by 56% in the atrial cells. In these two cell types, the membrane of the caveolae contains four times fewer intramembranous particles than the rest of the plasma membrane, and this difference applies to both PF and EF faces. The role of the caveolae is still unclear, but it does not seem that they have a pinocytotic function.