Desmosomal connectomics of all somatic muscles in an annelid larva

Cells form networks in animal tissues through synaptic, chemical and adhesive links. In muscle tissue, cells often connect through desmosomes, adhesive structures anchored by intermediate filaments. To study desmosomal networks, we reconstructed 852 muscle cells and their desmosomal partners by serial electron microscopy in an entire larva of the annelid Platynereis. Muscle cells adhere to each other, to epithelial, glial, ciliated, and bristle-producing cells and to the basal lamina, forming a desmosomal connectome of over 2,000 cells. The aciculae - chitin rods that form an endoskeleton in the segmental parapodia - are highly connected hubs in this network. This agrees with the many degrees of freedom of their movement, as revealed by video microscopy. Mapping motoneuron synapses to the desmosomal connectome highlighted the extent of tissue influenced by individual motoneuron classes. Our work shows how cellular-level maps of synaptic and adherent force networks can elucidate body mechanics.

Ssdp influences Wg expression and embryonic somatic muscle identity in Drosophila melanogaster

The somatic muscles of the Drosophila embryo and larvae share structural and functional similarities with vertebrate skeletal muscles and serve as a powerful model for studying muscle development. Here we show that the evolutionarily conserved Ssdp protein is required for the correct patterning of somatic muscles. Ssdp is part of the conserved Chi/LDB-Ssdp (ChiLS) complex that is a core component of the conserved Wg/Wnt enhanceosome, which responds to Wg signals to regulate gene transcription. Ssdp shows isoform specific expression in developing somatic muscles and its loss of function leads to an aberrant somatic muscle pattern due to a deregulated muscle identity program. Ssdp mutant embryos fail to maintain adequate expression levels of muscle identity transcription factors and this results in aberrant muscle morphology, innervation, attachment and fusion. We also show that the epidermal expression of Wg is downregulated in Ssdp mutants and that Ssdp interacts with Wg to regulate the properties of a subset of ventral muscles. Thus, our data unveil the dual contribution of Ssdp to muscle diversification by regulating the expression of muscle-intrinsic identity genes and by interacting with the extrinsic factor, Wg. The knowledge gained here about Ssdp and its interaction with Wg could be relevant to vertebrate muscle development.

Buccal capsule and intestine ultrastructure of the marine predatory nematode Sphaerolaimus balticus (Monhysterida: Sphaerolaimidae)

Summary The ultrastructural morphology of the buccal capsule and intestine (mid-gut) of the predatory marine nematode Sphaerolaimus balticus is investigated. The major part of the voluminous barrel-shaped buccal capsule is made up of strongly modified somatic cuticle and hence presents itself as an intricately differentiated cheilostome. The latter consists of three compartments: i.e., i) labial region; ii) striated region with six rows of fine longitudinal ribs; and iii) shagreen band penetrated by about ten projections of arcade tissue. The gymnostome and telostome are narrow and together constitute a small posterior portion of the buccal capsule. The mouth is evidently opened by contraction of anterior longitudinal somatic muscles. The intestine is characterised by a very thin and homogenous basal lamina. The cytoplasm of the enterocytes contains lipid granules, large electron-light vacuoles and rounded concentric inclusions in membranous vacuoles. Apical microvilli are separated from the lumen by a dense three-layered glycocalyx resembling the peritrophic membrane in the intestine of arthropods. The glycocalyx is only a supportive structure of the mid-gut. The most peculiar features of the intestine are the particularly strong junctions connecting the glycocalyx with the cells. The junctions appear as cytoplasmic bundles attached to the dense glycocalyx layer by dint of hemidesmosomes.

ACCUMULATION AND DISTRIBUTION OF NUTRIENTS IN THE MUSCLES AND HEPATOPANCREAS OF TWO-YEAR-OLD CARP (CYPRINUS CARPIO) FED WITH DIFFERENT RATIONS

The paper deals with the influence of different feed quality on the chemical composition and features of nutrient accumulation in the somatic muscles and hepatopancreas of two-yearold carp species. Fish were fed using pendulum auto-feeders on demand with K-111 compound feeds (23% protein and 3.5% fat) and Karp 38/12 (38% protein and 12% fat). In variant I, K-111 compound feed was used (in both car feeders), in variant II – Karp-38/12 (in both car feeders), in variant III–K-111 and Karp-38/12 (in different car feeders). The bionic method allows identifying the preference of fish for a particular type of feed. Regardless of the diets used, the water content in organs and tissues decreases during the growing of two-year-old carp species, which is primarily due to the accumulation of fat. To a lesser extent, this is due to the number of dry fat-free substance.

The Effect of Exercise on Pulpal and Gingival Blood Flow in Physically Active and Inactive Subjects as Assessed by Laser Doppler

The effects of exercise on pulpal and gingival blood flow are undefined. The autonomic nervous system response suggests that they could increase or decrease with exercise, and they may be independent of each other. This study attempts to answer these questions. Materials and Methods: 15 “physically active” subjects and 15 “physically inactive” subjects exercised on a treadmill. Laser Doppler recordings of pulpal and gingival blood flow were taken before and after exercise. Results: There was a mean increase of approximately 50% in both pulpal (range -66%-+509%) and gingival (-72%- +1022%) blood flow after exercise, with wide variations, with no significant differences between the two groups of subjects. Conclusion: Exercise could increase pulpal and/or gingival blood flow as part of the overall increase in cardiac output with exercise, or could decrease pulpal and/or gingival blood flow due to diversion of blood to the somatic muscles during exercise. This study suggests that the former physiological phenomenon usually takes place at both sites,though there were some contradictory results.

Vestigial Is Required during Late-Stage Muscle Differentiation in Drosophila melanogaster Embryos

The somatic muscles of Drosophila develop in a complex pattern that is repeated in each embryonic hemi-segment. During early development, progenitor cells fuse to form a syncytial muscle, which further differentiates via expression of muscle-specific factors that induce specific responses to external signals to regulate late-stage processes such as migration and attachment. Initial communication between somatic muscles and the epidermal tendon cells is critical for both of these processes. However, later establishment of attachments between longitudinal muscles at the segmental borders is largely independent of the muscle–epidermal attachment signals, and relatively little is known about how this event is regulated. Using a combination of null mutations and a truncated version of Sd that binds Vg but not DNA, we show that Vestigial (Vg) is required in ventral longitudinal muscles to induce formation of stable intermuscular attachments. In several muscles, this activity may be independent of Sd. Furthermore, the cell-specific differentiation events induced by Vg in two cells fated to form attachments are coordinated by Drosophila epidermal growth factor signaling. Thus, Vg is a key factor to induce specific changes in ventral longitudinal muscles 1–4 identity and is required for these cells to be competent to form stable intermuscular attachments with each other.