Contractile behavior of the forelimb digital flexors during steady-state locomotion in horses (Equus caballus): an initial test of muscle architectural hypotheses about in vivo function

The forelimb digital flexors of the horse display remarkable diversity in muscle architecture despite each muscle-tendon unit having a similar mechanical advantage across the fetlock joint. We focus on two distinct muscles of the digital flexor system: short compartment deep digital flexor (DDF(sc)) and the superficial digital flexor (SDF). The objectives were to investigate force-length behavior and work performance of these two muscles in vivo during locomotion, and to determine how muscle architecture contributes to in vivo function in this system. We directly recorded muscle force (via tendon strain gauges) and muscle fascicle length (via sonomicrometry crystals) as horses walked (1.7 m s(-1)), trotted (4.1 m s(-1)) and cantered (7.0 m s(-1)) on a motorized treadmill. Over the range of gaits and speeds, DDF(sc) fascicles shortened while producing relatively low force, generating modest positive net work. In contrast, SDF fascicles initially shortened, then lengthened while producing high force, resulting in substantial negative net work. These findings suggest the long fibered, unipennate DDF(sc) supplements mechanical work during running, whereas the short fibered, multipennate SDF is specialized for economical high force and enhanced elastic energy storage. Apparent in vivo functions match well with the distinct architectural features of each muscle.     

Sarcocystis mephitisi n. sp. (Protozoa: Sarcocystidae), Sarcocystis neurona-like and Toxoplasma-like infections in striped skunks (Mephitis mephitis)

Two structurally distinct types (A, B) of microscopic sarcocysts were found in muscles of 4 of 5 feral skunks. Type A sarcocysts had sarcocyst walls of up to 6 microm thick. The villar protrusions (Vp) on the sarcocyst wall were up to 5 microm long. The Vp were constricted at the base, expanded in the middle, and had a blunt tip. Numerous microtubules were present in the Vp and in the granular layer. Bradyzoites were up to 11 microm long and up to 3.2 microm wide. Based on the distinctiveness of the Vp, a new name, Sarcocystis mephitisi is proposed for type A sarcocysts. Type B sarcocysts had a relatively thin (approximately 1-2 microm thick) sarcocyst wall and the Vp were slender and tapered toward the tip. These sarcocysts were structurally similar to S. neurona sarcocysts. A Toxoplasma gondii-like tissue cyst was found in a section of tongue of 1 of the 4 skunks.     

Identification of a novel family of cell-surface proteins expressed in human vascular endothelium

Vascular endothelial cells (EC) play a key role in a variety of pathophysiologic processes, such as angiogenesis, inflammation, cancer metastasis, and vascular diseases. As part of a strategy to identify all genes expressed in human EC, a full-length cDNA encoding a potential secreted protein harboring 10 epidermal growth factor (EGF)-like domains and one CUB domain at the carboxyl terminus (termed, SCUBE1 for Signal peptide-CUB-EGF-like domain containing protein 1) was identified. SCUBE1 shares homology with several protein families, including members of the fibrillin and Notch families, and the anticoagulant proteins, thrombomodulin and protein C. SCUBE1 mRNA is found in several highly vascularized tissues such as liver, kidney, lung, spleen, and brain and is selectively expressed in EC by in situ hybridization. SCUBE1 is a secreted glycoprotein that can form oligomers and manifests a stable association with the cell surface. A second gene encoding a homologue (designated SCUBE2) was also identified and is expressed in EC as well as other cell types. SCUBE2 is also a cell-surface protein and can form a heteromeric complex with SCUBE1. Both SCUBE1 and SCUBE2 are rapidly down-regulated in EC after interleukin-1beta and tumor necrosis factor-alpha treatment in vitro and after lipopolysaccharide injection in vivo. Thus, SCUBE1 and SCUBE2 define an emerging family of human secreted proteins that are expressed in vascular endothelium and may play important roles in development, inflammation, and thrombosis.     

Hybrid origin of Japanese mice "Mus musculus molossinus": evidence from restriction analysis of mitochondrial DNA

The Japanese mouse, Mus musculus molossinus, has long been considered an independent subspecies of the house mouse. A survey of restriction- site haplotypes of mitochondrial DNA (mtDNA) showed that Japanese mice have two main maternal lineages. The most common haplotype is closely related to the mtDNA of the European subspecies M. m. musculus. The other common haplotype and two minor ones are closely related to each other and to the mtDNA of an Asiatic subspecies, M. m. castaneus. Two other rare variants are probably the result of recent contamination by European M. m. domesticus. The musculus type of mtDNA is found in the southern two-thirds of Japan, whereas the common castaneus type is found in the northern third and the minor variants are found sporadically throughout Japan. The castaneus mtDNA lineage had a few minor variants, whereas the musculus lineage was completely monomorphic. By contrast, the native population of M. m. castaneus and the Chinese and Korean musculus populations were highly polymorphic. These results suggest that M. m. molossinus is a hybrid between ancestral colonies, possibly very small, of M. m. musculus and M. m. castaneus, rather than an independent subspecies.      

Essentiality of insulin and prolactin for accumulation of rat casein mRNAs

Fetal calf serum (20%) does not substitute for insulin in terms of enhanced accumulation of rat casein mRNAs, but it can sustain the mammary tissue in culture. This property of fetal calf serum was utilized to show that in the presence of cortisol and 1) insulin or 2) prolactin, the delayed addition of prolactin or insulin, respectively, produced similar enhancement of 25 K and 42 K casein mRNAs. The results indicate that both insulin and prolactin are required for accumulation of rat casein mRNAs, the accumulation is independent of the sequence of addition of these hormones, and that the response cannot be ascribed entirely to the hormone added last.     

Interferon effects on microfilament organization cellular fibronectin distribution, and cell motility in human fibroblasts

We have shown previously (Pfeffer et al., 1979, Exp. Cell Res. 121:111-120) that treatment of human fibroblasts, planted at a density of 2x10(3) cells/cm(2), with purified human fibroblasts interferon (640 U/ml) for 3 d at 37 degrees C decreases the overall rate of cell proliferation to 35-40 percent of the control value. In the present experiments we have characterized the phenotype of interferon-inhibited fibroblasts. The mean volume of trypsinized, interferon-treated cells was increased 31 percent abover that of control cells. The interferon-treated population was much more heterogeneous than the control population with respect to volume, and there was a considerable overlap in the volume distributions of the two populations. The cell surface area was, on the average, increased 65 percent after interferon treatment. More than 80 percent of the treated cells had enlarged nuclei, many of which were lobed, and the fraction of binucleated cells was increased fivefold. After interferon treatment, over 40 percent of the cells showed large actin-containing fibers in the form of multiple parallel arrays. Fewer than 5 percent of the control cells contained such large actin fibers. The number of actin fibers of all sizes was tripled in the treated fibroblasts on a per cell basis and, calculated per unit surface area of the cells, the number was increased 82 percent. In contrast, 10-nm filaments and microtubules did not appear to be increased in number per unit surface area of the cells. The increases per cell in the abundance of these structures were directly related to increased cell size. After interferon treatment, fibronection was distributed in arrays of long filaments covering most portions of the cell surface. Interferon treatment markedly decreased the rate of cell locomotion as well as membrane ruffling and saltatory movements of intracellular granules.