Loss of thick filaments from fast-twitch glucolytic muscle fibers of the pigeon pectoralis after chronic administration of dantrolene sodium.

Adult pigeons received dantrolene sodium, a skeletal muscle relaxant which blocks the release of calcium during excitation-contraction coupling, for 12 to 16 weeks. The pectoralis muscles of these birds were analyzed for changes occurring in the various fiber types of the muscle. Both histochemistry (ATPase and SDH activity) and electron microscopy (mitochondrial and lipid volume percentages) differentiated two fiber types. The two fiber-types consisted of fast-twitch glycolytic fibers (FG) and fast-twitch oxidative-glycolytic (FOG) fibers. After dantrolene treatment some FG fibers showed little or no ATPase activity. Dantrolene treatment also produced a disappearance of thick filaments in some FG fibers. We infer that the fibers without thick filaments are the ones lacking ATPase activity. The FOG fibers were nearly normal. Since drug-fed birds lose weight, a few birds were starved to determine whether the filament loss was related solely to the bird's loss in weight. No fibers in starved birds showed reduced ATPase activity or loss of thick filaments. In fibers that showed thick filament disappearance, the I-bands remained organized and intact, suggesting that the I-band maintains its integrity without interaction with the thick filaments. Changes in activity patterns may cause loss of thick filaments by inhibiting either their synthesis or assembly.     

Genes encoding peroxisomal enzymes are not necessarily assigned on the same chromosome of an n-alkane-utilizable yeast Candida tropicalis

We have resolved eight chromosomal bands from an n-alkane-assimilating yeast, Candida tropicalis pK 233, by using contour-clamped homogeneous electric field gel electrophoresis (CHEF). From the results of hybridization of DNA probes of yeast peroxisomal enzymes--catalase, acyl-CoA oxidase, carnitine acetyltransferase, isocitrate lyase, malate synthase, acetoacetyl-CoA thiolase, and 3-ketoacyl-CoA thiolase--to Southern transfers of CHEF gels, these genes were proven not necessarily to be located on the same chromosome. This fact shows that the genes encoding the enzymes tested were not distributed to be cistronic, although simultaneous and inducible synthesis of peroxisomal enzymes occurred in harmony with the proliferation of peroxisomes, suggesting that their co-ordinated expression might be mainly regulated by certain trans-acting factors.     

Peroxisomal isocitrate lyase of the n-alkane-assimilating yeast Candida tropicalis: gene analysis and characterization

A genomic DNA clone encoding isocitrate lyase, a key enzyme of the glyoxylate cycle and a peroxisomal enzyme of the n-alkane-assimilating yeast Candida tropicalis has been isolated with a cDNA probe from the yeast lambda EMBL library. Nucleotide sequence analysis of the genomic DNA clone disclosed that the region coding isocitrate lyase had a length of 1,650 base pairs, corresponding to 550 amino acids (61,602 Da). RNA blot analysis demonstrated that only one kind of mRNA (2 kb) supposed to be transcribed from this gene was present in the cells. A comparison of the amino acid sequences was made with the isocitrate lyase of castor bean, one of the glyoxysomal enzymes, and the enzyme of E. coli. The isocitrate lyases of C. tropicalis and castor bean had high homology, and the presence of some amino acid stretches conserved in all three enzymes suggests that these might be involved in the catalysis of the common reaction. There was an insertion common to the isocitrate lyases of C. tropicalis and castor bean, which is of interest concerning their evolution. In the C-terminal region, a characteristic sequence similar to that previously proposed as the import signal to peroxisomes was present.     

Tenotomy of the avian anterior latissimus dorsi muscle. II. Can regeneration from the stump occur in the pigeon?

Because the chick's anterior latissimus dorsi muscle (ALD) regenerates a fast-twitch muscular connection after tenotomy, the pigeon's ALD was tenotomized, either at the origin or through the muscle 0.5 cm from the origin, to determine whether this muscle behaves similarly to the chick muscle. These procedures were compared in pigeons operated upon at 7 weeks, versus 5 to 9 months of age. The pigeon's ALD did not regenerate a new connection, and other differences were observed between the pigeon and chick ALD. The pigeon ALD has only a single slow muscle-fiber type, has fewer fast fibers, and transforms to a fast-twitch muscle more readily than the chick ALD after tenotomy. The transformation of muscle fiber types occurred more readily in the older pigeons than those tenotomized at 7 weeks of age. Tenotomy induced morphological alterations of the muscle fiber structure in all of the pigeons, which is in contrast to the absence of changes in the tenotomized chick ALD. Therefore the pigeon and chick ALD respond completely differently to tenotomy.     

Phylogeography of Fischer’s blue,Tongeia fischeri,in Japan: Evidence for introgressive hybridization

The widespread lycaenid butterfly Tongeia fischeri is distributed from eastern Europe to northeastern Asia and represented by three geographically isolated populations in Japan. In order to clarify the phylogeographic history of the species, we used sequences of three mitochondrial (COI, Cyt b and ND5) and two nuclear (Rpl5 and Ldh) genes of 207 individuals collected from 55 sites throughout Japan and five sites on the Asian continent. Phylogenetic trees and the median-joining network revealed six evolutionary mitochondrial haplotype clades, which corresponded to the geographic distribution of the species. Common ancestors of Japanese T. fischeri might have come to Japan during the mid-Pleistocene by multiple dispersals of continental populations, probably via a land bridge or narrow channel between western Japan and the Korean Peninsula. The geographical patterns of variation of mitochondrial and nuclear markers are discordant in northeastern Kyushu, possibly as a result of introgressive hybridization during the ancient contact between the Kyushu and Shikoku populations in the last glacial maximum. The phylogeographic pattern of T. fischeri in Japan are probably related to the geological history, Pleistocene climatic oscillations and distribution of the host plant.     

Sclerochronological study of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from Hokkaido,northern Japan

Here, we present the first sclerochronological investigation of shells of the gigantic inoceramids Sphenoceramus schmidti and S. sachalinensis from the middle Campanian cold seep carbonate‐bearing strata of the Yezo Basin in Hokkaido (northern Japan). Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotope values were measured in the aragonitic and calcitic shell layers of both species and compared to those of other co‐occurring benthic (mainly bivalves and gastropods) and demersal molluscs (ammonites). Sedimentological and stable isotope data suggest that these bivalves lived near cold seeps and were exposed to high H₂S level in the seawater. The inoceramid shells exhibited higher δ¹³C and lower δ¹⁸O values than the coeval non‐cold seep molluscs. We ascribed the anomalous isotopic pattern to a combination of vital and environmental effects determined by the hosting of chemosymbionts and the exposure to warm interstitial waters. Inoceramid δ¹³C minima coincided with growth lines and likely reflect changes in nutrient supply by the chemosymbionts. Absolute temperatures estimated from δ¹⁸O values of Sphenoceramus schmidti and S. sachalinensis were, on average, ca. 4–5°C warmer than those reconstructed for the non‐seepage environment (19.3 ± 0.7°C). Short‐term δ¹⁸O fluctuations of the inoceramid material indicate local temperature ranges of up to 5.2°C, that is four times larger than those reconstructed from the benthic and demersal fauna (1.3°C). In general, our data suggest that the stable carbon and oxygen isotope values of the studied Sphenoceramus spp. were strongly affected by short‐term fluctuations in seepage activity and do not reflect seasonal fluctuations.     

Phylogenetic relationships of Australian skinks of the Mabuya group (Reptilia: Scincidae) inferred from mitochondrial DNA sequences

Portions of two mitochondrial genes (12S and 16S ribosomal RNAs) were sequenced to analyze the phylogenetic relationships of the Mabuya group from the Australian region (Corucia, Egernia and Tiliqua). Results indicated the monophyly of these genera and their divergence from Asian and African members of this group. This suggests that the diversity of the Mabuya group in the Australian region has increased through an endemic radiation, not through multiple colonizations from outside. Among the genera from this region, Corucia and Tiliqua were closest to each other. This result contradicts with those of the previous hypotheses on the basis of morphological and immunological data that, respectively, suggested closest affinities between Corucia and Egernia, and Egernia and Tiliqua. We suppose that the morphological characters exclusively joining Corucia and Egernia are actually in plesiomorphic state.     

Fiber type composition of four hindlimb muscles of adult Fisher 344 rats

 The limb and trunk muscles of adult rats express four myosin heavy chain (MHC) isoforms, one slow (MHCI) and three fast (MHCIIa, MHCIId, and MHCIIb). The distribution of these isoforms correlates with fiber types delineated using myofibrillar actomyosin adenosine triphosphatase (mATPase) histochemistry. For example, type I fibers express MHCI and fiber types IIA, IID, and IIB express MHCIIa, MHCIId, and MHCIIb, respectively. Fibers containing only one MHC isoform have been termed ”pure” fibers. Recent evidence suggests that a population of ”hybrid” fibers exist in rat skeletal muscle which contain two MHC isoforms. The purpose of the present investigation was to document the entire range of histochemically defined ”pure” and ”hybrid” fiber types in untreated muscles of the young adult Fisher 344 rat hindlimb. The selected hindlimb muscles (soleus, tibialis anterior, extensor digitorum longus, and gastrocnemius muscles) were removed from 12 male rats and analyzed for muscle fiber type distribution, cross-sectional area, and MHC content. Care was taken to delineate eight fiber types (I, IC, IIC, IIA, IIAD, IID, IIDB, and IIB) using refined histochemical techniques. Hybrid fibers were found to make up a considerable portion of the muscles examined (a range of 8.8–17.8% of the total). The deep red portion of the gastrocnemius muscle contained the largest number of hybrid fibers, most of which were the fast types IIAD (8.5±2.8%) and IIDB (5.2±2.3%). In conclusion, hybrid fibers make up a considerable portion of normal rat limb musculature and are an important population that should not be ignored. Accepted: 15 October 1998