The localization of a peroxidase associated with hard cuticle formation in an insect, Calpodes ethlius stoll, Lepidoptera, Hesperiidae

The distribution of a peroxidase associated with the formation of hard cuticle has been studied in developing larvae of Calpodes ethlius. It occurs in granules in several cell types but is most easily observed in the cells making the proleg spines at the 4th to 5th molt. Light microscopy shows peroxidase in numerous granules about 0.5mu in diameter at the time the cuticle of the spine shaft is being deposited. Electron microscopy shows these granules to be multivesicular bodies with peroxidase in the matrix. Peroxidase is also found in cisternae of the rough ER near Golgi complexes, in vesicles of Golgi complexes and in the secretory vesicles which discharge to make cuticle at the apical surface. The cuticle above the plasma membrane where peroxidase is being deposited reacts with DAB in the absence of hydrogen peroxide. Presumably this cuticle has been 'peroxidized' as a first stage in stabilization by cross-linking. Some of the peroxidase secreted at the apical surface is pinocytosed and transported to the multivesicular bodies, suggesting that there may be a precise control of the cuticular environment through the turnover of its soluble components.     

Vertebrate golgi complexes have beads in a similar position to those found in arthropods

Insects and other arthropods have bead-like structures in Golgi complexes from all cell types. They are arranged in rings at the base of transition vesicles located near the smooth surface of the rough endoplasmic reticulum making the forming face of the Golgi complex and are only seen easily after staining in bismuth salts. Procedures used to demonstrate the beads in arthropod Golgi complexes do not selectively stain any structures where they would be expected to occur in several mouse and tadpole tissues. However, a faint pattern similar to the arthropod GC beads can be made out in the large GCs concerned in the formation of acrosomes during mouse spermatogenesis. Uranyl staining shows particles of about the same size and spacing as the beads of arthropod GCs. We conclude that vertebrate GCs may have beads that differ from arthropods in their staining properties.     

The development of branched silk gland nuclei

Nuclei in the giant polyploid silk gland cells of Calpodes ethlius grow by endomitosis and can develop hundreds of branches during larval life. The shape of the these nuclei is characteristic for each region of the gland. We have found shape to be correlated with arrangement of the nuclear matrix. Scanning electron microscopy showed nuclear matrices with shapes similar to those of feulgen stained nuclei. Profiles of isolated matrices seen by transmission electron microscopy had filaments aligned parallel to the long axis of nuclear branches. DNA stained by Hoechst had a similar parallel alignment within the branches. Nuclear shape may be maintained by a small number of components, since electrophoretic analysis showed only a few abundant polypeptides in the matrix fraction. Silk gland nuclei have some of the same nuclear matrix antigens found in smaller, more regularly shaped, eukaryote nuclei.     

PORE CANALS AND RELATED STRUCTURES IN INSECT CUTICLE

The fine structure and the distribution of an esterase have been studied in the cuticle of Galleria larvae, Tenebrio larvae and pupae, and in the wax-secreting cuticle of the honey bee, and compared with those in the cuticle of the caterpillar of Calpodes. In Galleria and Tenebrio the pore canals are spaces passing through the lamellate endocuticle from the epithelium to the epicuticle. They contain a filament from the cells which may be concerned in their formation. The shape of the pore canal is probably determined by the orientation of the fibres making up the lamellae in the endocuticle and is not a regular helix. The pore canals also contain numerous filaments of another sort which pass on through the epicuticle and are believed to be the origin of the surface wax. They are particularly abundant in the pore canals of the honey bee wax-secreting cuticle and extend into the cell in long pockets surrounded by an envelope of the plasma membrane. The esterase is probably concerned with the final stage of wax synthesis, for its distribution is similar to that of the lipid filaments.     

Dystrobrevin is required postsynaptically for homeostatic potentiation at the Drosophila NMJ

Evolutionarily conserved homeostatic systems have been shown to modulate synaptic efficiency at the neuromuscular junctions of organisms. While advances have been made in identifying molecules that function presynaptically during homeostasis, limited information is currently available on how postsynaptic alterations affect presynaptic function. We previously identified a role for postsynaptic Dystrophin in the maintenance of evoked neurotransmitter release. We herein demonstrated that Dystrobrevin, a member of the Dystrophin Glycoprotein Complex, was delocalized from the postsynaptic region in the absence of Dystrophin. A newly-generated Dystrobrevin mutant showed elevated evoked neurotransmitter release, increased bouton numbers, and a readily releasable pool of synaptic vesicles without changes in the function or numbers of postsynaptic glutamate receptors. In addition, we provide evidence to show that the highly conserved Cdc42 Rho GTPase plays a key role in the postsynaptic Dystrophin/Dystrobrevin pathway for synaptic homeostasis. The present results give novel insights into the synaptic deficits underlying Duchenne Muscular Dystrophy affected by a dysfunctional Dystrophin Glycoprotein complex.     

Sperm competition and the evolution of ejaculate composition

We present a model of sperm competition that incorporates both sperm and nonsperm parts of the ejaculate. Our primary focus is on determining how ejaculate composition and size evolves as a function of the effects of seminal fluid on male reproductive success and as a function of asymmetry in sperm usage by females. The model predicts that different patterns of investment in sperm and seminal products are expected to evolve as a function of the bias in sperm usage by females. It also predicts the evolution of distinct patterns in ejaculate composition depending on the function of seminal fluid. In the discussion, we highlight a number of potential approaches for testing the theory that we develop.     

Evolution of sexual dimorphism in phenotypic covariance structure in Phymata

Sexual dimorphism is a consequence of both sex‐specific selection and potential constraints imposed by a shared genetic architecture underlying sexually homologous traits. However, genetic architecture is expected to evolve to mitigate these constraints, allowing the sexes to approach their respective optimal mean phenotype. In addition, sex‐specific selection is expected to generate sexual dimorphism of trait covariance structure (e.g., the phenotypic covariance matrix, P ), but previous empirical work has not fully addressed this prediction. We compared patterns of phenotypic divergence, for three traits in seven taxa in the insect genus Phymata (Reduviidae), to ask whether sexual dimorphism in P is common and whether its magnitude relates to the extent of sexual dimorphism in trait means. We found that sexual dimorphism in both mean and covariance structure was pervasive but also that the multivariate distance between sex‐specific means was correlated with sex differences in the leading eigenvector of P , while accounting for uncertainty in phylogenetic relationships. Collectively, our findings suggest that sexual dimorphism in covariance structure may be a common but underappreciated feature of dioecious populations.