Effects of FABP knockdown on flight performance of the desert locust, Schistocerca gregaria.

During migratory flight, desert locusts rely on fatty acids as their predominant source of energy. Lipids mobilized in the fat body are transported to the flight muscles and enter the muscle cells as free fatty acids. It has been postulated that muscle fatty acid binding protein (FABP) is needed for the efficient translocation of fatty acids through the aqueous cytosol towards mitochondrial ß-oxidation. To assess whether FABP is required for this process, dsRNA was injected into freshly emerged adult males to knock down the expression of FABP. Three weeks after injection, FABP and its mRNA were undetectable in flight muscle, indicating efficient silencing of FABP expression. At rest, control and treated animals exhibited no morphological or behavioral differences. In tethered flight experiments, both control and treated insects were able to fly continually in the initial, carbohydrate-fueled phase of flight, and in both groups, lipids were mobilized and released into the hemolymph. Flight periods exceeding 30 min, however, when fatty acids become the main energy source, were rarely possible for FABP-depleted animals, while control insects continued to fly for more than 2 h. These results demonstrate that FABP is an essential element of skeletal muscle energy metabolism in vivo.

Photoreceptor layer of salmonid fishes: transformation and loss of single cones in juvenile fish.

The retinas of many vertebrates have cone photoreceptors that express multiple visual pigments. In many of these animals, including humans, the original cones to appear in the retina (which express UV or blue opsin) may change opsin types, giving rise to new spectral phenotypes. Here we used microspectrophotometry and in situ hybridization with cDNA probes to study the distribution of UV and blue cones in the retinas of four species of Pacific salmon (coho, chum, chinook, and pink salmon), in the Atlantic salmon, and in the rainbow/steelhead trout. In Pacific salmon and in the trout, all single cones express a UV opsin at hatching (lambda(max) of the visual pigment approximately 365 nm), and these cones later transform into blue cones by opsin changeover (lambda(max) of the blue visual pigment approximately 434 nm). Cones undergoing UV opsin downregulation exhibit either of two spectral absorbance profiles. The first is characterized by UV and blue absorbance peaks, with blue absorbance dominating the base of the outer segment. The second shows UV absorbance diminishing from the outer segment tip to the base, with no sign of blue absorbance. The first absorbance profile indicates a transformation from UV to blue phenotype by opsin changeover, while the second type suggests that the cone is undergoing apoptosis. These two events (transformation and loss of corner cones) are closely associated in time and progress from ventral to dorsal retina. Each double cone member contains green (lambda(max) approximately 510 nm) or red (lambda(max) approximately 565 nm) visual pigment (double cones are green/red pairs), and, like the rods (lambda(max) approximately 508 nm), do not exhibit opsin changeover. Unlike Pacific salmonids, the Atlantic salmon shows a mixture of UV and blue cones and a partial loss of corner cones at hatching. This study establishes the UV-to-blue cone transformation as a general feature of retinal growth in Pacific salmonids (genus Oncorhynchus).

Characterization of a new fatty acid response element that controls the expression of the locust muscle FABP gene.

In vertebrate and invertebrate muscles, the expression of fatty acid binding proteins (FABP) is induced by long chain fatty acids. To identify the fatty acid response elements that mediate this up-regulation, the gene of the FABP expressed in locust flight muscle was cloned, and its upstream sequences analyzed for potential regulatory elements. Comparison with other muscle FABP promoters revealed the presence of a 19-bp imperfect inverted repeat sequence that contains two hexanucleotide half sites (AGTGGT and ATGGGA), interspersed by 3 nucleotides. The promoter activity was studied with reporter gene constructs in L6 myoblasts, in which H-FABP expression is stimulated by long-chain fatty acids in a similar manner as in adult cardiomyocytes. The 19 bp element, located 180 bp upstream of the transcription start site, was found to be essential for the fatty acid induction of gene expression, and gel shift analysis confirmed that this fatty acid response element is capable of binding nuclear proteins both from rat myoblasts and locust muscle in the presence of fatty acids. A similar, but reverse sequence that is present upstream of all mammalian H-FABP promoters may modulate the expression of the rat H-FABP gene.