Abstract. We have examined the cytoskeletal architecture and its relationship with synaptic vesicles in synapses by quick-freeze deep-etch electron microscopy (QF.DE). The main cytoskeletal elements in the presynaptic terminals (neuromuscular junction, electric organ, and cerebellar cortex) were actin filaments and microtubules. The actin filaments formed a network and frequently were associated closely with the presynaptic plasma membranes and active zones. Short, linking strands ~30 nm long were found between actin and synaptic vesicles, between microtubules and synaptic vesicles. Fine strands (30-60 nm) were also found between synaptic vesicles. Frequently spherical structures existed in the middle of the strands between synaptic vesicles. Another kind of strand (~100 nm long, thinner than the actin filaments) between synaptic vesicles and plasma membranes was also observed. We have examined the molecular structure of synapsin ~ and its relationship with actin filaments, microtubules, and synaptic vesicles in vitro using the low angle rotary shadowing technique and QF.DE. The synapsin 1, *47 nm long, was composed of a head (~14 nm diam) and a tail (~33 nm long), having a tadpole-like appearance. The high resolution provided by QF.DE revealed that a single synapsin 1 cross-linked actin filaments and linked actin filaments with synaptic vesicles, forming ~30-nm short strands. The head was on the actin and the tail was attached to the synaptic vesicle or actin filament. Microtubules were also cross-linked by a single syr~apsin 1, which also connected a microtubule to synaptic vesicles, forming •30 nm strands. The spherical head was on the microtubules and the tail was attached to the synaptic vesicles or to microtubules. Synaptic vesicles incubated with synapsin 1 were linked with each other via fine short fibrils and frequently we identified spherical structures from which two or three fibrils radiated and cross-linked synaptic vesicles.We have ex,~mined the localization of synapsin 1 using ultracryomicrotomy and colloidal gold-immunocytochemistr:~ ~ anti-synapsin 1 IgG. Synapsin 1 was exclusively localized in the regions occupied by synaptic vesicles. Statistical analyses indicated that synapsin 1 is located mostly at least *30 nm away from the presynaptic membrane. These data derived via, three different approaches suggest that synapsin 1 could be a main element of short linkages between actin filaments and synaptic vesicles, and between microtubules and synaptic vesicles; and between synaptic vesicles in the nerve terminals. The longer strands (*100 nm): associated with presynaptic membrane could consist of other proteins, most probably fodrin, judging from its structure. Because phosphorylation of synapsin 1 by Ca++/calmodulin-dependent kinase detaches synapsin 1 from vesicles it could release synaptic vesicles from actin filaments, microtubules and other synaptic vesicles, and thus increase the mobility of synaptic vesicles to the premy.naptie' membrane after depolarization dependent influx of Ca. ~+ into ...

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Caveolin-3 is a muscle-specific protein integrated in the caveolae, which are small invaginations of the plasma membrane. Mutations of the caveolin-3 gene, localized at 3p25, have been reported to be involved in the pathogenesis of limb-girdle muscular dystrophy (LGMD1C or caveolinopathy) with mild clinical symptoms, inherited through an autosomal dominant form of genetic transmission. To elucidate the pathogenetic mechanism, we developed caveolin-3-deficient mice for use as animal models of caveolinopathy. Caveolin-3 mRNA and its protein were absent in homozygous mutant mice. In heterozygous mutant mice, both the mRNA and its protein were normal in size, but their amounts were reduced by about half. The density of caveolae in skeletal muscle plasma membrane was roughly proportional to the amount of caveolin-3. In homozygous mutant mice, muscle degeneration was recognized in soleus muscle at 8 weeks of age and in the diaphragm from 8 to 30 weeks, although there was no difference in growth and movement between wild-type and mutant mice. No apparent muscle degeneration was observed in heterozygous mutant mice, indicating that pathological changes caused by caveolin-3 gene disruption were inherited through the recessive form of genetic transmission.

Amino acid transport system L has been proposed to be one of the major nutrient transport systems at the blood-brain barrier. Using immunohistochemical analyses, a system L transporter LAT1 was shown to be expressed in the brain capillary endothelial cells in rats. Because LAT1 was coexpressed with 4F2 heavy chain which brings LAT1 to the plasma membrane, LAT1 is proposed to be functional in the plasma membrane of brain capillary endothelial cells. Both LAT1 and 4F2hc immunoreactivities were detected in a double line appearance surrounding endothelial cell nuclei, suggesting both proteins are present in the luminal and abluminal membranes. LAT1 is, thus, a blood-brain barrier system L transporter responsible for the permeation of aromatic or branched-chain amino acids and amino acid-related drugs such as L-DOPA.

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ST and BPTB autografts were able to reproduce the native size of the ACL mid-substance cross-sectional area. The ST-G graft was significantly larger than the ACL cross-sectional area. For clinical relevance, ST and BPTB grafts are recommended in order to reproduce the native size of the ACL in anatomical ACL reconstruction with autograft.

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SummaryPlectin 1 links intermediate filaments to costameric sarcolemma through β-synemin, α-dystrobrevin and actin