No abstract

2B) with large differences inWe conclude that pig muscles express high proportions of fast MHC isoforms, including MHC-2B, and that Vo values are higher than expected on the basis of the scaling relationship between contractile parameters and body size.

This study was aimed to achieve a definitive and unambiguous identification of fiber types in canine skeletal muscles and of myosin isoforms that are expressed therein. Correspondence of canine myosin isoforms with orthologs in other species as assessed by base sequence comparison was the basis for primer preparation and for expression analysis with RT-PCR. Expression was confirmed at protein level with histochemistry, immunohistochemistry, and SDS-PAGE combined together and showed that limb and trunk muscles of the dog express myosin heavy chain (MHC) type 1, 2A, and 2X isoforms and the so-called "type 2dog" fibers express the MHC-2X isoform. MHC-2A was found to be the most abundant isoform in the trunk and limb muscle. MHC-2X was expressed in most but not all muscles and more frequently in hybrid 2A-2X fibers than in pure 2X fibers. MHC-2B was restricted to specialized extraocular and laryngeal muscles, although 2B mRNA, but not 2B protein, was occasionally detected in the semimembranosus muscle. Isometric tension (P(o)) and maximum shortening velocity (V(o)) were measured in single fibers classified on the basis of their MHC isoform composition. Purified myosin isoforms were extracted from single muscle fibers and characterized by the speed (V(f)) of actin filament sliding on myosin in an in vitro motility assay. A close proportionality between V(o) and V(f) indicated that the diversity in V(o) was due to the different myosin isoform composition. V(o) increased progressively in the order 1/slow < 2A < 2X < 2B, thus confirming the identification of the myosin isoforms and providing their first functional characterization of canine muscle fibers.

Antarctic krill (Euphausia superba Dana) is a key species in the Antarctic food web and occurs on a circumcontinental scale. Population genetic structure of this species was investigated by sequence analysis of the ND1 mitochondrial gene in four population samples collected at di¡erent geographical localities around the Antarctic continent. Results indicate the existence of signi¢cant genetic di¡erences between samples, and we suggest that oceanographic barriers could be su¤ciently strong and temporally stable to restrict gene £ow between distinct areas. Moreover, our data indicate that Antarctic krill is not at mutation^drift equilibrium and that the species possibly has a low e¡ective population size as compared to the census size.

This study aimed to analyse the expression of myosin heavy chain (MHC) isoforms in bovine muscles, with particular attention to the MHC-2B gene. Diaphragm, longissimus dorsi, masseter, several laryngeal muscles and two extraocular muscles (rectus lateralis and retractor bulbi) were sampled in adult male Bos taurus (age 18-24·months, mass 400-500·kg) and analysed by RT-PCR, gel electrophoresis and immunohistochemistry. Transcripts and proteins corresponding to eight MHC isoforms were identified: MHC-␣ ␣ and MHC-␤ ␤/slow (or MHC-1), two developmental isoforms (MHC-embryonic and MHC-neonatal), three adult fast isoforms (MHC-2A