Freeze-fracture study of the lateral-line canal organ of the Japanese sea eel,Lincozymba nystromi

Summary Specializations of apical surfaces of hair cells, supporting cells and marginal cells in the lateral-line canal organ of Japanese sea eel, Lincozymba nystromi, were examined with a freeze-fracture technique. Apical surfaces of hair cells have a lower density of intramembrane particles (IMP) than those of the surrounding supporting cells. Density of IMP on the streocilia is almost the same as that on the apical surface of hair cells. Junctions between hair and supporting cells were tighter than those between two supporting cells; those between supporting and marginal cells were tighter than those between hair and supporting cells, and those between two marginal cells were the tightest in the lateral-line canal organ.     

Rejection of B16 melanoma induced by expression of a transfected major histocompatibility complex class I gene.

Transfection of a functional major histocompatibility complex class I gene into certain tumor cells, induced by oncogenic viruses or chemical carcinogens, can effectively abrogate their tumorigenic activity. Since experimentally induced tumors possess strong tumor-specific transplantation antigens, expression of cell surface class I antigens may present the tumor cells to appropriate immune effector cells. Most spontaneously arising tumors do not possess tumor-specific transplantation antigens, and their tumorigenicity may not be affected by the expression of a transfected class I gene. We demonstrate that the poorly immunogenic B16-BL6 melanoma can be rendered nontumorigenic in syngeneic mice by the expression of the class I H-2K antigen but not the class II I-A antigen. Furthermore, the poorly tumorigenic, class I-expressing B16-BL6-transfected cells can effectively immunize syngeneic C57BL/6 mice against the highly tumorigenic, class I-deficient B16-BL6 parental cells. Our success in experimentally manipulating the tumorigenicity of a spontaneously derived neoplasm offers hope for a potential modality for the effective treatment of human cancer.     

Canopy photosynthetic production in a Japanese larch stand. I. Seasonal and vertical changes of leaf characteristics along the light gradient in a canopy

In an 18 year old Japanese larch stand, leaf characteristics such as area, weight, gross photosynthetic rate and respiration rate were studied in order to obtain basic information on estimating canopy photosynthesis and respiration. The leaf growth courses in area and weight from bud opening were approximated by simple logistic curves. The growth coefficient for the area growth curve was 0.155–0.175 day⁻¹, while that for the weight growth was 0.112–0.117 day⁻¹. The larger growth coefficient in area growth caused the seasonal change in specific leaf area (SLA) that increased after bud opening to its peak early in May at almost 300 cm² g⁻¹ and then decreased until it leveled off at about 140 cm²g⁻¹. The change inSLA indicates the possibility that leaf area growth precedes leaf thickness growth. The relationship between the coefficientsa andb of the gross photosynthetic rate (p)-light flux density (1) curve (p=bI/(1+aI)) and the mean relative light flux density (I′/I ₀) at each canopy height were approximated by hyperbolic formulae:a=A/(I′/I ₀)+B andb=C/(I′/I ₀)+D. Leaf respiration rate was also increased with increasingI′/I ₀. Seasonal change of gross photosynthetic rate and leaf respiration rate were related to mean air temperature through linear regression on semilogarithmic co-ordinates.     

The interaction of maleimidobenzoyl G-actin with myosin subfragment 1 in solution: characterization of the MgATPase activity after chemical crosslinking.

As is well known, the ATPase/structural interactions between the S-1 moieties of myosin molecules ("cross bridges") and actin molecules in polymerized ("F") form are thought to underlie muscle contraction. It is surmised that such interactions are unitary (1 S-1:1 actin), but actual demonstration thereof is handicapped by intrinsic properties of the proteins. It is known that monomeric ("G" form) actin binds to S-1 and that in this contact only the 633-642 region of S-1 is involved; however, such unions do not activate S-1 ATPase. Recently, Bettache et al. (1989) [Proc. Natl. Acad. Sci. USA 86, 6028-6032] showed that chemically modified actin can be kept in monomeric form, and makes a stable unitary complex with S-1, but without activating S-1 ATPase. In this paper, however, we show that when such complexes are covalently crosslinked by 1-ethyl-3-[3-(dimethylamino)-propyl]carbodiimide they recover activated ATPase. The existence of such activated complexes proves an excellent model system as a soluble analogue of the F-actin-(S-1) complex.     

Structural aspects of skeletal muscle F-actin as studied by tryptic digestion: evidence for a second nucleotide interacting site

Trypsin was used as a probe of F-actin conformation. F-actin is known to be refractory to proteolysis [Jacobson, G.R. and Rosenbusch, J.P. (1976) Proc. Natl. Acad. Sci. U.S. 73, 2742-2746]. However, here it was found that F-actin could also be digested by trypsin to a 33-kDa fragment (like G-actin) when free MgADP is present in the medium. The amounts of degradation of F-actin depended on the ADP concentration; saturation occurred at about 0.5 mM. Elimination of divalent cations from the medium completely suppressed the effect of ADP on the digestion of F-actin. Other nucleotides were also examined. The effect decreased in the order ADP greater than ATP much greater than IDP greater than GDP = UDP. Adenine, adenosine, AMP, and PPi had no effect at all. epsilon-ADP had the effect, and its fluorescence was changed on the addition of F-actin. The intrinsic tryptophan fluorescence spectrum of F-actin was ADP-dependent. These results suggest the presence of a second nucleotide interacting site on actin and that ADP interaction at this site induces conformational changes in monomeric actin molecule in F-actin filaments.     

Enhanced transcription in a pre-B-like cell line transformed with cloned antibody genes after antigen-specific stimulation

The transducing vector, pSV2-neo, carrying the rearranged immunoglobulin (Ig) heavy (mu) and light (kappa) chain genes specific for the hapten 2,4,6-trinitrophenyl (TNP) was introduced into a pre-B cell line. The transformants expressed the TNP-specific IgM receptor on the surface. Furthermore, the addition of TNP-bovine serum albumin (hapten-carrier conjugate) to the culture media activated the expression of the transferred Ig genes and several endogenous genes such as v-abl and beta-tubulin. However, expression of the beta2-microglobulin gene was not affected. The results presented in this paper show that transfection of cloned Ig genes into B cells is a useful system for establishing monoclonal B cell lines expressing functional Ig receptor molecules with defined hapten specificity.     

Mouse immunoglobulin gene rearrangements. The sequence of a nonexpressed lambda 3-chain gene

A functionally defective lambda 3-immunoglobulin chain gene has been cloned from plasmacytoma HOPC-1 (gamma 2b, lambda 1). The lambda 3 gene resulted from the juxtaposition of the germline V lambda 1 sequence with a J lambda 3 C lambda 3 gene segment. DNA sequencing of the rearranged V lambda 1 J lambda 3 exon showed the presence of a single base pair deletion at the site of V-J joining. The alteration in the reading frame caused by this deletion generated a stop codon at the 3' end of J lambda 3, thus rendering this gene nonfunctional for light chain production. In addition, a one-point mutation in the J lambda 3-C lambda 3 intron distinguishes the rearranged gene from the unrearranged counterpart. The implications that this rearrangement has in terms of the mechanism of somatic mutations and of selective proliferation of B cells mediated by antigen stimulation are discussed.