The complete mitochondrial genome of Schizothorax chongi (Fang, 1936) (Teleostei, Cyprinidae, Schizothoracinae).

Schizothorax chongi is an endemic and important polyploidy fish in the upper stream of the Yangtze River. S. chongi represents a typical model species to study historical adaptation and evolution in the Tibetan Plateau. In this study, the complete mitochondrial DNA genome sequence of S. chongi was first determined by DNA sequencing based on the PCR fragments. The complete mitochondrial DNA (mtDNA) genome sequence of S. chongi is a circular molecule of 16,584 bp in length. It consists of 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region (D-loop). The gene nucleotide composition of S. chongi is 29.6% A, 27.1% C, 17.9% G, and 25.4% T, with a high AT content (55.0%). The results could provide useful data for further studies on phylogenetics, conservation genetics and rational resource management for S. chongi.

The complete mitochondrial genome of Glyptothorax sinense (Siluriformes, Sisoridae).

Glyptothorax sinense (Siluriformes, Sisoridae), is a kind of small-sized freshwater fish which mainly distributes in the middle and upper reaches of the Yangtze River in China. In this study, the complete mitochondrial genome of G. sinense was first determined using a PCR-based method. The complete mtDNA sequence is 16,531 bp in length, including 22 transfer RNA genes, 2 ribosomal RNA genes, 13 protein-coding genes, and a non-coding control region (D-loop). The overall-based composition was 31.61% A, 26.66% T, 15.38% G and 26.34% C, with a relatively high A + T content (58.27%). This will provide a useful tool for evolutionary and population genetic studies of G. sinense.

The complete mitochondrial genome sequence of Triplophysa anterodorsalis (Teleostei, Balitoridae, Nemacheilinae).

Triplophysa anterodorsalis is an endemic fish in the upper stream of the Yangtze River, Jinsha River and its tributaries. However, wild populations of T. anterodorsalis declined sharply due to cascade hydropower stations constructed successively in the Jinsha River during the past decades. In the present study, the complete mitochondrial DNA genome sequence of T. anterodorsalis was first determined by DNA sequencing based on the PCR fragments. The complete mitochondrial genome sequence of T. anterodorsalis is a circular molecule of 16,567 bp in size. It consists of 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region (D-loop). The gene nucleotide composition of T. anterodorsalis is 27.37% A, 25.68% C, 18.37% G, and 28.57% T, with a relatively a relatively high A + T content (55.94%). The results could provide useful data for studies on genetic structure and diversity and rational resource conservation in T. anterodorsalis.

Characterization of the complete mitochondrial genome sequence of Homatula potanini (Cypriniformes, Nemacheilidae, Nemachilinae).

Homatula potanini is an endemic and one of ornamental fishes in the upper stream of the Yangtze River and its tributaries. However, wild populations of H. potanini declined sharply due to anthropological activity in the Jinsha River during the past decades. In present study, the complete mitochondrial DNA genome sequence of H. potanini was first determined by DNA sequencing based on the PCR fragments. The complete mitochondrial genome sequence is a circular molecule of 16,569 bp in size. It consists of 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes, and a control region (D-loop). The gene nucleotide composition of H. potanini is 30.1% A, 26.9% C, 16.7% G, and 26.3% T, with a relatively high A + T content (56.4%). The results could provide useful data for studies on genetic structure and rational resource conservation in H. potanini.

Juvenile hormone regulates body size and perturbs insulin signaling in Drosophila.

The role of juvenile hormone (JH) in regulating the timing and nature of insect molts is well-established. Increasing evidence suggests that JH is also involved in regulating final insect size. Here we elucidate the developmental mechanism through which JH regulates body size in developing Drosophila larvae by genetically ablating the JH-producing organ, the corpora allata (CA). We found that larvae that lack CA pupariated at smaller sizes than control larvae due to a reduced larval growth rate. Neither the timing of the metamorphic molt nor the duration of larval growth was affected by the loss of JH. Further, we show that the effects of JH on growth rate are dependent on the forkhead box O transcription factor (FOXO), which is negatively regulated by the insulin-signaling pathway. Larvae that lacked the CA had elevated levels of FOXO activity, whereas a loss-of-function mutation of FOXO rescued the effects of CA ablation on final body size. Finally, the effect of JH on growth appears to be mediated, at least in part, via ecdysone synthesis in the prothoracic gland. These results indicate a role of JH in regulating growth rate via the ecdysone- and insulin-signaling pathways.

Plastic flies: the regulation and evolution of trait variability in Drosophila.

Individuals within species and populations vary. Such variation arises through environmental and genetic factors and ensures that no two individuals are identical. However, it is clear that not all traits show the same degree of intraspecific variation. Some traits, in particular secondary sexual characteristics used by males to compete for and attract females, are extremely variable among individuals in a population. Other traits, for example brain size in mammals, are not. Recent research has begun to explore the possibility that the extent of phenotypic variation (here referred to as "variability") may be a character itself and subject to natural selection. While these studies support the concept of variability as an evolvable trait, controversy remains over what precisely the trait is. At the heart of this controversy is the fact that there are very few examples of developmental mechanisms that regulate trait variability in response to any source of variation, be it environmental or genetic. Here, we describe a recent study from our laboratory that identifies such a mechanism. We then place the study in the context of current research on the regulation of trait variability, and discuss the implications for our understanding of the developmental regulation and evolution of phenotypic variation.

FOXO regulates organ-specific phenotypic plasticity in Drosophila.

Phenotypic plasticity, the ability for a single genotype to generate different phenotypes in response to environmental conditions, is biologically ubiquitous, and yet almost nothing is known of the developmental mechanisms that regulate the extent of a plastic response. In particular, it is unclear why some traits or individuals are highly sensitive to an environmental variable while other traits or individuals are less so. Here we elucidate the developmental mechanisms that regulate the expression of a particularly important form of phenotypic plasticity: the effect of developmental nutrition on organ size. In all animals, developmental nutrition is signaled to growing organs via the insulin-signaling pathway. Drosophila organs differ in their size response to developmental nutrition and this reflects differences in organ-specific insulin-sensitivity. We show that this variation in insulin-sensitivity is regulated at the level of the forkhead transcription factor FOXO, a negative growth regulator that is activated when nutrition and insulin signaling are low. Individual organs appear to attenuate growth suppression in response to low nutrition through an organ-specific reduction in FOXO expression, thereby reducing their nutritional plasticity. We show that FOXO expression is necessary to maintain organ-specific differences in nutritional-plasticity and insulin-sensitivity, while organ-autonomous changes in FOXO expression are sufficient to autonomously alter an organ's nutritional-plasticity and insulin-sensitivity. These data identify a gene (FOXO) that modulates a plastic response through variation in its expression. FOXO is recognized as a key player in the response of size, immunity, and longevity to changes in developmental nutrition, stress, and oxygen levels. FOXO may therefore act as a more general regulator of plasticity. These data indicate that the extent of phenotypic plasticity may be modified by changes in the expression of genes involved in signaling environmental information to developmental processes.

The 19-amino acid cassette of cyclooxygenase-2 mediates entry of the protein into the endoplasmic reticulum-associated degradation system.

Cyclooxygenase (COX) isoforms catalyze the committed step in prostaglandin biosynthesis. The primary structures of COX-1 and COX-2 are very similar except that COX-2 has a 19-amino acid (19-AA) segment of unknown function located just inside its C terminus. Here we provide evidence that the major role of the 19-AA cassette is to mediate entry of COX-2 into the ER-associated degradation system that transports ER proteins to the cytoplasm. COX-1 is constitutively expressed in many cells, whereas COX-2 is usually expressed inducibly and transiently. In murine NIH/3T3 fibroblasts, we find that COX-2 protein is degraded with a half-life (t(1/2)) of about 2 h, whereas COX-1 is reasonably stable (t(1/2) > 12 h); COX-2 degradation is retarded by 26 S proteasome inhibitors. Similarly, COX-1 expressed heterologously in HEK293 cells is quite stable (t(1/2) > 24 h), whereas COX-2 expressed heterologously is degraded with a t(1/2) of approximately 5 h, and its degradation is slowed by proteasome inhibitors. A deletion mutant of COX-2 was prepared lacking 18 residues of the 19-AA cassette. This mutant retains native COX-2 activity but, unlike native COX-2, is stable in HEK293 cells. Conversely, inserting the COX-2 19-AA cassette near the C terminus of COX-1 yields a mutant ins594-612 COX-1 that is unstable (t(1/2) approximately 3 h). Mutation of Asn-594, an N-glycosylation site at the beginning of the 19-AA cassette, stabilizes both COX-2 and ins594-612 COX-1; nonetheless, COX mutants that are glycosylated at Asn-594 but lack the remainder of the 19-amino acid cassette (i.e. del597-612 COX-2 and ins594-596 COX-1) are stable. Thus, although glycosylation of Asn-594 is necessary for COX-2 degradation, at least part of the remainder of the 19-AA insert is also required. Finally, kifunensine, a mannosidase inhibitor that can block entry of ER proteins into the ER-associated degradation system, retards COX-2 degradation.