Tyrosine storage vacuoles in insect fat body

The watery vacuoles first described from larval insect fat body (Chironomus, Voinov, 1927; Aedes, Wigglesworth, 1942; Rhodnius, Wigglesworth, 1967) have been studied in 4th and 5th stage Calpodes larvae. The vacuoles arise at the beginning (E+6–24 hr) of the 4th stadium from plasma membrane infolds that separate from the cell surface as provacuoles less than 1 μm in diameter. These provacuoles grow and fuse with one another through the intermolt until about half the volume of each fat body cell is occupied by a single, large vacuole. The vacuoles begin to disappear at molting. Their membrane is either incorporated into the plasma membrane by exocytosis or fragmented into vesicles that fuse to become lamellar bodies where the membranes are presumably digested. All the vacuoles have gone by a few hours after ecdysis.The tyrosine content of the fat body increases and decreases in proportion to the size of the vacuoles. As the vacuoles decrease at molting the titre of tyrosine in the hemolymph is transiently elevated at the time when there is most demand for phenolics for cuticle stabilization. Crystals having the form of tyrosine crystallize out from vacuoles separated from the fat body. In fat body extracts separated by thin layer chromatography, similar crystals occur only in the eluates from spots corresponding to tyrosine. The vacuoles are therefore presumed to be tyrosine stores used in cuticle stabilization at molting. They correspond to a type of aqueous storage compartment that is well known in plants but hitherto little recognized in animal cells.     

Heat stress inhibits skeletal muscle hypertrophy

Heat shock proteins (Hsps) are molecular chaperones that aid in protein synthesis and trafficking and have been shown to protect cells/tissues from various protein damaging stressors. To determine the extent to which a single heat stress and the concurrent accumulation of Hsps influences the early events of skeletal muscle hypertrophy, Sprague-Dawley rats were heat stressed (42 degrees C, 15 minutes) 24 hours prior to overloading 1 plantaris muscle by surgical removal of the gastrocnemius muscle. The contralateral plantaris muscles served as controls. Heat-stressed and/or overloaded plantaris muscles were assessed for muscle mass, total muscle protein, muscle protein concentration, Type I myosin heavy chain (Type I MHC) content, as well as Hsp72 and Hsp25 content over the course of 7 days following removal of the gastrocnemius muscle. As expected, in non-heat-stressed animals, muscle mass, total muscle protein and MHC I content were significantly increased (P < 0.05) following overload. In addition, Hsp25 and Hsp72 increased significantly after 2 and 3 days of overload, respectively. A prior heat stress-elevated Hsp25 content to levels similar to those measured following overload alone, but heat stress-induced Hsp72 content was increased significantly greater than was elicited by overload alone. Moreover, overloaded muscles from animals that experienced a prior heat stress showed a lower muscle mass increase at 5 and 7 days; a reduced total muscle protein elevation at 3, 5, and 7 days; reduced protein concentration; and a diminished Type I MHC content accumulation at 3, 5, and 7 days relative to nonheat-stressed animals. These data suggest that a prior heat stress and/or the consequent accumulation of Hsps may inhibit increases in muscle mass, total muscle protein content, and Type I MHC in muscles undergoing hypertrophy.     

Molecular and morphological evidence for the Holarctic distribution of Urogonimus macrostomus (Rudolphi, 1803) Monticelli, 1888 (Digenea: Leucochloridiidae)

Species of Urogonimus Monticelli, 1888 (Leucochloridiidae Poche, 1907) are difficult to distinguish using adult morphology, and their taxonomy has been repeatedly subjected to revision. Some Nearctic species have been regarded as synonymous with the Palearctic type species Urogonimus macrostomus (Rudolphi, 1803) Monticelli, 1888. This implies that U. macrostomus is present in the Nearctic, but there is no additional evidence for this putative distribution. We collected trematodes morphologically indistinguishable from U. macrostomus from a house sparrow (Passer domesticus) in Edmonton, Alberta, Canada. Sequences 2958 bp in total length from the small and large subunits of ribosomal DNA from 2 specimens were 99.8-100% identical to those of U. macrostomus in the Ukraine and Japan. In light of the lack of morphological differences and small degree of genetic variation, we consider the specimens we collected to be conspecific with U. macrostomus in the Palearctic, and the Holarctic range of the species is thus supported. Sequences from a more rapidly evolving gene, cytochrome c oxidase 1, were obtained to aid future study of this and related species.     

Heteromeric, but not homomeric, connexin channels are selectively permeable to inositol phosphates

Previous work has shown that channels formed by both connexin (Cx)26 and Cx32 (heteromeric Cx26/Cx32 hemichannels) are selectively permeable to cAMP and cGMP. To further investigate differential connexin channel permeability among second messengers, and the influence of connexin channel composition on the selectivity, the permeability of inositol phosphates with one to four phosphate groups through homomeric Cx26, homomeric Cx32, and heteromeric Cx26/Cx32 channels was examined. Connexin channels were purified from transfected HeLa cells and from rat, mouse, and guinea pig livers, resulting in channels with a broad range of Cx26/Cx32 aggregate ratios. Permeability to inositol phosphates was assessed by flux through reconstituted channels. Surprisingly, myoinositol and all inositol phosphates tested were permeable through homomeric Cx32 and homomeric Cx26 channels. Even more surprising, heteromeric Cx26/Cx32 channels showed striking differences in permeability among inositol phosphates with three or four phosphate groups and among isomers of inositol triphosphate. Thus, heteromeric channels are selectively permeable among inositol phosphates, whereas the corresponding homomeric channels are not. There was no discernible difference in the permeability of channels with similar Cx26/Cx32 ratios purified from native and heterologous sources. The molecular selectivity of heteromeric channels among three inositol triphosphates could not be accounted for by simple connexin isoform stoichiometry distributions and therefore may depend on specific isoform radial arrangements within the hexameric channels. Dynamic regulation of channel composition in vivo may effectively and efficiently modulate intercellular signaling by inositol phosphates.     

Linkage disequilibrium and heritability of copy-number polymorphisms within duplicated regions of the human genome

Studies of copy-number variation and linkage disequilibrium (LD) have typically excluded complex regions of the genome that are rich in duplications and prone to rearrangement. In an attempt to assess the heritability and LD of copy-number polymorphisms (CNPs) in duplication-rich regions of the genome, we profiled copy-number variation in 130 putative "rearrangement hotspot regions" among 269 individuals of European, Yoruba, Chinese, and Japanese ancestry analyzed by the International HapMap Consortium. Eighty-four hotspot regions, corresponding to 257 bacterial artificial chromosome (BAC) probes, showed evidence of copy-number differences. Despite a predisposing genetic architecture, no polymorphism was ever observed in the remaining 46 "rearrangement hotspots," and we suggest these represent excellent candidate sites for pathogenic rearrangements. We used a combination of BAC-based and high-density customized oligonucleotide arrays to resolve the molecular basis of structural rearrangements. For common variants (frequency >10%), we observed a distinct bias against copy-number losses, suggesting that deletions are subject to purifying selection. Heritability estimates did not differ significantly from 1.0 among the majority (30 of 34) of loci analyzed, consistent with normal Mendelian inheritance. Some of the CNPs in duplication-rich regions showed strong LD with nearby single-nucleotide polymorphisms (SNPs) and were observed to segregate on ancestral SNP haplotypes. However, LD with the best available SNP markers was weaker than has been reported for deletion polymorphisms in less complex regions of the genome. These observations may be accounted for by a low density of SNP data in duplicated regions, challenges in mapping and typing the CNPs, and the possibility that CNPs in these regions have rearranged on multiple haplotype backgrounds. Our results underscore the need for complete maps of genetic variation in duplication-rich regions of the genome.