Characteristics of the nuclear (18S, 5.8S, 28S and 5S) and mitochondrial (12S and 16S) rRNA genes of Apis mellifera (Insecta: Hymenoptera): structure, organization, and retrotransposable elements

As an accompanying manuscript to the release of the honey bee genome, we report the entire sequence of the nuclear (18S, 5.8S, 28S and 5S) and mitochondrial (12S and 16S) ribosomal RNA (rRNA)-encoding gene sequences (rDNA) and related internally and externally transcribed spacer regions of Apis mellifera (Insecta: Hymenoptera: Apocrita). Additionally, we predict secondary structures for the mature rRNA molecules based on comparative sequence analyses with other arthropod taxa and reference to recently published crystal structures of the ribosome. In general, the structures of honey bee rRNAs are in agreement with previously predicted rRNA models from other arthropods in core regions of the rRNA, with little additional expansion in non-conserved regions. Our multiple sequence alignments are made available on several public databases and provide a preliminary establishment of a global structural model of all rRNAs from the insects. Additionally, we provide conserved stretches of sequences flanking the rDNA cistrons that comprise the externally transcribed spacer regions (ETS) and part of the intergenic spacer region (IGS), including several repetitive motifs. Finally, we report the occurrence of retrotransposition in the nuclear large subunit rDNA, as R2 elements are present in the usual insertion points found in other arthropods. Interestingly, functional R1 elements usually present in the genomes of insects were not detected in the honey bee rRNA genes. The reverse transcriptase products of the R2 elements are deduced from their putative open reading frames and structurally aligned with those from another hymenopteran insect, the jewel wasp Nasonia (Pteromalidae). Stretches of conserved amino acids shared between Apis and Nasonia are illustrated and serve as potential sites for primer design, as target amplicons within these R2 elements may serve as novel phylogenetic markers for Hymenoptera. Given the impending completion of the sequencing of the Nasonia genome, we expect our report eventually to shed light on the evolution of the hymenopteran genome within higher insects, particularly regarding the relative maintenance of conserved rDNA genes, related variable spacer regions and retrotransposable elements

Effects of age and gender on shortening velocity and myosin isoforms in single rat muscle fibres

The maximum velocity of unloaded shortening (V0) and the myosin heavy chain (MyHC) and light chain (MyLC) isoform composition were determined in single fibres from soleus and extensor digitorum longus (EDL) muscles of male and female rats 3–6 and 22–24 months old. In the soleus muscle, the β/slow (type I MyHC) isoform predominated in both young and old animals, irrespective of gender. In the EDL, fibres expressing type IIX MyHC or a combination of IIX and IIB (IIXB) MyHC isoforms were predominant in old rats, while type IIB MyHC fibres predominated in young individuals of both genders. The V0 of soleus fibres expressing the type I MyHC isoform decreased (P < 0.001) by 40% with age in spite of an unchanged MyLC composition. In the EDL, the V0 of fibres expressing IIX, IIXB and IIB MyHC isoforms did not change with age or differ between males and females. In conclusion, similar age-related changes in V0 and MyHC composition were observed in single muscle cells from both male and female rats. The present results demonstrate that the relationship between V0 and MyHC isoform composition at the single fibre level is similar in male and female rats, and that similar qualitative changes take place during ageing in both genders. Motor impairment, such as slowing of muscle movement and increasing muscle weakness, is a prominent feature of ageing. Consequently, many elderly people have difficulties in performing activities of daily life, maintaining postural balance and preventing impending falls. This, together with the age-related decrease in bone strength, which has been suggested to be related to muscle weakness (Madsen et al. 1993), increases the risk of bone fractures in the elderly. The problems may be even greater in women than in men, since men are generally stronger than women at any age (Miller et al. 1993), and consequently women are at greater risk of becoming impaired in certain motor tasks with ageing (Rantanen et al. 1996). The mechanisms underlying these impairments are complex, but alterations within the motor neurone and muscle cell play an important role. An understanding of the age-related changes in skeletal muscle becomes increasingly important in the light of the growing population of elderly people. The maximum velocity of unloaded shortening (V0) is one of the most important design parameters of skeletal muscle, since muscles develop their maximum power at approximately one-third of V0 (Rome et al. 1990). Thus, to generate power optimally over a wide range of movements, it is crucial to be able to recruit muscle fibres with a wide range of V0. The V0 of a muscle is proportional to the myosin adenosine triphosphatase (ATPase) activity (Bárány 1967). The activity of myosin ATPase is determined by the myosin heavy chain (MyHC) isoform composition, and there is a close correlation between V0 and this composition at the single fibre level (Reiser et al. 1985, Greaser et al. 1988, Sweeney et al. 1988, Schluter & Fitts 1994). Ageing has been reported to have different effects in muscles of male and female mammals, including man (Beltran Niclos et al. 1995, Cartee 1995, Phillips et al. 1996). Most studies on the effects of age and gender on skeletal muscle have been focused on differences in maximum force (Miller et al. 1993, Phillips et al. 1996a,b; Rantanan et al. 1996) and muscle size (Cartee 1995). However, the effects of age and gender on the shortening velocity have received less scientific attention and the studies published so far have dealt with changes in the velocity of whole muscle movement (e.g. Beltran Niclos et al. 1995). Measurements of skeletal muscle function in vivo are limited by factors that tend to obscure the behaviour of individual muscle fibres, such as (i) intramuscular differences in fibre orientation, (ii) differences in the mechanical leverage provided by the bony anatomy of the joint, (iii) the elasticity of the muscle and its tendons and, during voluntary contractions, (iv) differences in patterns of motor unit recruitment and (v) activation of antagonistic muscles. In addition, the roles of different fibre types in whole muscle contraction are difficult to evaluate. These confounding factors are circumvented in skinned fibre preparations which allow investigation of the function of the myofilament proteins in a cell with an intact filament lattice under near physiological conditions. In this study the effects of age and gender on the contractile speed and expression of myosin isoforms in skinned single fibres were investigated. On the basis of previous observations indicating that male and female rats exhibited similar age-related changes in the composition of myosin isoforms in both fast- and slow-twitch skeletal muscles (Larsson & Yu 1997), it was hypothesized that V0 and its relation to the MyHC composition of single extensor digitorum longus (EDL) and soleus muscle fibres from female rats would follow the same pattern as that of their male counterparts