Dual role of the coactivator TORC2 in modulating hepatic glucose output and insulin signaling

Under fasting conditions, the cAMP-responsive CREB coactivator TORC2 promotes glucose homeostasis by stimulating the gluconeogenic program in liver. Following its nuclear translocation in response to elevations in circulating glucagon, TORC2 regulates hepatic gene expression via an association with CREB on relevant promoters. Here, we show that, in parallel with their effects on glucose output, CREB and TORC2 also enhance insulin signaling in liver by stimulating expression of the insulin receptor substrate 2 (IRS2) gene. The induction of hepatic IRS2 during fasting appears critical for glucose homeostasis; knockdown of hepatic IRS2 expression leads to glucose intolerance, whereas hepatic IRS2 overexpression attenuates the gluconeogenic program and reduces fasting glucose levels. By stimulating the expression of IRS2 in conjunction with gluconeogenic genes, the CREB:TORC2 pathway thus triggers a feedback response that limits glucose output from the liver during fasting.     

Susceptibility of captive adult winter-run Chinook salmon Oncorhynchus tshawytscha to waterborne exposures with infectious hematopoietic necrosis virus (IHNV)

Sexually mature female Chinook salmon Oncorhynchus tshawytscha with no prior history of exposure to infectious hematopoietic necrosis virus (IHNV) were susceptible to experimental infection induced by additions of virus to the water. The resulting infections resembled those observed among naturally infected hatchery and wild populations of Chinook salmon. Virus was detected as early as 4 d post-exposure (p.e.) and subsequently in all virus-exposed fish that died or that were examined at 14 d p.e. when the study was terminated. The greatest concentrations of virus, up to 10(8) plaque-forming units (pfu) ml(-1), were found in the ovarian fluid at 13 to 14 d p.e., but the virus was also found in high concentrations in the gill, kidney/spleen and plasma. In contrast, the virus was not recovered from unexposed control adult salmon that died or were sampled at the end of the study. Despite detecting concentrations of IHNV in excess of 10(7) pfu g(-1) of tissue, no specific microscopic lesions were found in IHNV-exposed compared to unexposed control salmon. The results of this initial study suggest that virus in the spawning environment, either from adult salmon or other sources, may contribute to its rapid spread among adult Chinook salmon, thereby considerably increasing the prevalence of IHNV infection in both wild and hatchery populations of adult Chinook salmon.     

Myxobolus cerebralis internal transcribed spacer 1 (ITS-1) sequences support recent spread of the parasite to North America and within Europe

Molecular approaches for resolving relationships among the Myxozoa have relied mainly on small subunit (SSU) ribosomal DNA (rDNA) sequence analysis. This region of the gene is generally used for higher phylogenetic studies, and the conservative nature of this gene may make it inadequate for intraspecific comparisons. Previous intraspecific studies of Myxobolus cerebralis based on molecular analyses reported that the sequence of SSU rDNA and the internal transcribed spacer (ITS) were highly conserved in representatives of the parasite from North America and Europe. Considering that the ITS is usually a more variable region than the SSU, we reanalyzed available sequences on GenBank and obtained sequences from other M. cerebralis representatives from the states of California and West Virginia in the USA and from Germany and Russia. With the exception of 7 base pairs, most of the sequence designated as ITS-1 in GenBank was a highly conserved portion of the rDNA near the 3-prime end of the SSU region. Nonetheless, the additional ITS-1 sequences obtained from the available geographic representatives were well conserved. It is unlikely that we would have observed virtually identical ITS-1 sequences between European and American M. cerebralis samples had it spread naturally over time, particularly when compared to the variation seen between isolates of another myxozoan (Kudoa thyrsites) that has most likely spread naturally. These data further support the hypothesis that the current distribution of M. cerebralis in North America is a result of recent introductions followed by dispersal via anthropogenic means, largely through the stocking of infected trout for sport fishing.     

Estimation of relative fitnesses from relative risk data and the predicted future of haemoglobin alleles S and C

Epidemiological studies of genetic differences in disease susceptibility often estimate the relative risks (RR) of different genotypes. Here I provide an approach to calculate the relative fitnesses of different genotypes based on RR data so that population genetic approaches may be utilized with these data. Using recent RR data on human haemoglobin beta genotypes from Burkina Faso, this approach is used to predict changes in the frequency of the haemoglobin sickle-cell S and C alleles. Overall, it generally appears that allele C will quickly replace the S allele in malarial environments. Explicit population genetic predictions suggest that this replacement may occur within the next 50 generations in Burkina Faso.     

Phylogenetic comparison of the myxosporea based on an actin cDNA isolated from Myxobolus cerebralis

The full-length actin gene from Myxobolus cerebralis (McerAct-1), the first characterized from representatives in the phylum Myxozoa, encodes a 378-amino acid polypeptide with an estimated molecular weight of 41,580-Da. A phylogenetic comparison found M. cerebralis to branch outside the metazoans. This finding contrasts with previous reports that suggest an evolutionary affinity of the Myxozoa with either the Bilateria or Cnidaria.     

The Xenopus laevis cortical granule lectin: cDNA cloning, developmental expression, and identification of the eglectin family of lectins

A Xenopus laevis egg cortical granule, calcium-dependent, galactosyl-specific lectin participates in forming the fertilization layer of the egg envelope and functions in establishing a block to polyspermy. We report the cDNA cloning of the lectin, expression of the cortical granule lectin gene during oogenesis and early development, and identification of a new family of lectins. The translated cDNA for the cortical granule lectin had a signal peptide, a structural sequence of 298 amino acids, a molecular weight of 32.7 K, contained consensus sequence sites for N-glycosylation and a fibrinogen domain. The lectin cDNA was expressed during early stages of oogenesis. Lectin glycoprotein levels were constant during development with 2/3 of the lectin associated with the extracellular perivitelline space and the egg/embryo fertilization envelope. Lectin mRNA levels were from 100- to 1000-fold greater in ovary than in other adult tissues. The lectin had no sequence homology to the previously identified lectin families. The lectin had 41-88% amino acid identity with nine translated cDNA sequences from an ascidian, lamprey, frog, mouse, and human. Based on the conserved carbohydrate binding and structural properties of these glycoproteins, we propose a new family of lectins, the eglectin family.     

In vivo interactions of apoA-II, apoA-I, and hepatic lipase contributing to HDL structure and antiatherogenic functions

Studies with mice have revealed that increased expression of apolipoprotein A-II (apoA-II) results in elevations in high density lipoprotein (HDL), the formation of larger HDL, and the development of early atherosclerosis. We now show that the increased size of HDL results in part from an inhibition of the ability of hepatic lipase (HL) to hydrolyze phospholipids and triglycerides in the HDL and that the ratio of apoA-I to apoA-II determines HDL functional and antiatherogenic properties. HDL from apoA-II transgenic mice was relatively resistant to the action of HL in vitro. To test whether HL and apoA-II influence HDL size independently, combined apoA-II transgenic/HL knockout (HLko) mice were examined. These mice had HDL similar in size to apoA-II transgenic mice and HLko mice, suggesting that they do not increase HDL side by independent mechanisms. Overexpression of apoA-I from a transgene reversed many of the effects of apoA-II overexpression, including the ability of HDL to serve as a substrate for HL. Combined apoA-I/apoA-II transgenic mice exhibited significantly less atherosclerotic lesion formation than did apoA-II transgenic mice. These results were paralleled by the effects of the transgenes on the ability of HDL to protect against the proinflammatory effects of oxidized low density lipoprotein (LDL). Whereas nontransgenic HDL protected against oxidized LDL induction of adhesion molecules in endothelial cells, HDL from apoA-II transgenic mice was proinflammatory. HDL from combined apoA-I/apoA-II transgenic mice was equally as protective as HDL from nontransgenic mice. Our data suggest that as the ratio of apoA-II to apoA-I is increased, the HDL become larger because of inhibition of HL, and lose their antiatherogenic properties.     

MHC variation and tissue transplantation in fish

Major histocompatibility complex (MHC) genes were originally discovered because of their role in tissue rejection in mammals and have subsequently been implicated in the incidence of autoimmune diseases and resistance to infectious diseases. Here we present the first demonstration that a gene defined by molecular sequence in the fish MHC, specifically a class II locus, plays an important role in tissue rejection. This effect in the endangered Gila topminnows appears to be additive and depends on the number of MHC alleles shared between the host and the recipient fish of the scale transplants. In addition, there was lower success of scale transplants in MHC-matched individuals in a population with high microsatellite variation than in a population with low variation. This suggests that other loci, presumably other MHC loci, play a significant role in transplantation success in fishes, as they do in mammals.     

Founder effect in an island population of bighorn sheep

The Tiburon Island population of desert bighorn sheep has increased in size from 20 founders in 1975 to approximately 650 in 1999. This population is now the only population being used as the source stock for transplantations throughout northern Mexico. To evaluate the genetic variation in this population, we examined 10 microsatellite loci and a major histocompatibility complex (MHC) locus. The genetic variation was significantly less than found in other populations of the same subspecies in Arizona. Using a model that takes into account the effects of genetic drift on genetic distance, most of the genetic distance observed between the Tiburon population and Arizona samples could be explained. Because of the low genetic variation found in the Tiburon population, it is suggested that the Tiburon population should be supplemented with additional unrelated animals or that the transplant populations should be supplemented with unrelated animals.     

Establishing a captive broodstock for the endangered bonytail chub (Gila elegans)

It is crucial for endangered species to retain as much genetic variation as possible to enhance recovery. Bonytail chub (Gila elegans) is one the most imperiled freshwater fish species, persisting as a declining population of large and old individuals primarily in Lake Mohave on the lower Colorado River. Establishment of a new captive broodstock from the 1981 F1 progeny of at most 10 wild fish plus any newly captured wild fish is evaluated and reviewed. The effective number of founders contributing to the 1981 F1 progeny appears quite small, varying from approximately 3.5, based on F1 allozyme data and supported by mtDNA data, to approximately 8.5, based on the original production records. Using a sample of these progeny to initiate a new broodstock further reduces the effective number of founders. With even the most optimistic evaluation of the amount of genetic variation in F1 progeny, it is obvious that including wild fish in the broodstock is essential to increase the amount of genetic variation. The approach given here could be applied to retain genetic variation in other endangered species in a captive broodstock until they have stable natural populations of adequate size.