Comparative evolution of muscular dystrophy in diaphragm, gastrocnemius and masseter muscles from old male mdx mice.

X chromosome-linked muscular dystrophic mdx mouse lacks the sarcolemmal protein dystrophin and represents a genetic homologue of human Duchenne muscular dystrophy (DMD). The present study analysed some aspects of pathological processes such as fibrosis, frequency of centralized nuclei, presence of degenerative or regenerative fibres, expression of utrophin and associated protein complexes, and myosin heavy chain isoforms in three muscles [diaphragm (DIA), gastrocnemius (GTC) and masseter (MAS)] from old male mdx mice. All parameters investigated comparatively in these pathological muscles provided evidence that the MAS mdx muscle presents a slight deterioration pattern in comparison to that of DIA and GTC muscles. Utrophin and associated proteins are present in many cell clusters with continuous membrane labelling in MAS muscle. Respective proportions of myosin heavy chain isoforms, measured by electrophoresis/densitometry, showed only slight change in GTC muscle, significant evolution in DIA muscle but drastic isoform conversions in MAS muscle. These results highlighted the difference in deterioration susceptibility of various muscles to muscular dystrophy. The reason why this occurs in MAS muscles is still obscure and discussed in terms of the comparative developmental origins of these muscles.

Stereotaxic atlas of the pig brain.

A stereotaxic atlas of the pig brain has been established. It consists of 60 frontal and 18 sagittal drawings illustrating Nissl stained sections. A stereotaxic apparatus adapted for the Pig was used to determine the brain coordinates. Radiographic techniques were applied to verify the correct position of the central nervous structures in the apparatus. The zero horizontal plane contains the line joining the recessus preopticus and the posterior commissure (PC) images. These two landmarks were identified by ventriculography. The anterior limit of the PC is used as zero on the stereotaxic atlas. Vertical electrode trajectories implanted at a fixed depth in the brain and at different anterior and lateral levels were used to determine the lateral, vertical and height coordinates in the different planes. Then the brains were perfused and embedded to avoid major displacement of the cerebral structures. Frontal and sagittal serial sections of 100 microns were performed in two different animals. Magnified diagrams of brain sections representing the cellular architecture of the brain structures were produced, some of which are illustrated with photomicrographs. For certain areas, the limits of the nuclei were difficult to determine even when complementary electrophysiological studies were carried out. Each plate is accompanied by a list of abbreviations used to label structures on the plate, together with the terms which they represent. This work should provide a useful anatomical guide for research on the pig brain.

Differential expression of myosin heavy chain mRNA and protein isoforms in four functionally diverse rabbit skeletal muscles during pre- and postnatal development.

Myosin heavy chains (hcs) are the major determinant in the speed of contraction of skeletal muscle, and various isoforms are differentially expressed depending on the functional activity of the muscle. Using the rapid amplification of cDNA ends (3' RACE) method, we have characterised the 3' end of the embryonic, perinatal, type 1, 2a, 2x, and 2b myosin hc genes in rabbit skeletal muscle and used them as probes in RNase protection assays to quantitatively monitor their expression in different type of skeletal muscles just before and after birth. SDS PAGE was used to study the changes in the expression level of their respective protein and to determine the relative abundance of each myosin hc isoform in the muscles studied. The results show that for each anatomical muscle, the developmental changes in myosin hc gene expression at the mRNA level correlate strongly to those observed at the protein level. By studying their developmental expression in four functionally diverse skeletal muscles (semimembranosus proprius, diaphragm, tibialis anterior, and semimembranosus accessorius), it was shown that all muscles express the embryonic, perinatal, and type 1 isoform during prenatal development up to the E27 stage. In the diaphragm, low levels of the type 2a and 2x transcripts, which are adult fast isoforms, were also detected at the E27 stage. During the first week of postnatal growth the myosin hc transition leading to the expression of the adult isoforms is complex, and as many as five different myosin heavy chains are concurrently expressed in some muscles at around birth. As the animal matures, individual muscles become adapted to perform highly specialised functions, and this is reflected in the myosin hc composition within these muscles. Accordingly, the expression of the type 1 isoform, and the sequence of appearance and the expression levels of the type 2 isoforms, were exclusively dependent on the muscle type and largely reflect the functional activity of each muscle during the postnatal growth period.