Differential translatability of antifreeze protein mRNAs in a transgenic host

Expression of two self-enhancing antifreeze proteins from the beetle Dendroides canadensis in Drosophila melanogaster

Antifreeze proteins (AFPs) lower the freezing point of water without affecting the melting point. This difference between melting point and freezing point has been termed thermal hysteresis. Antifreeze protein genes, dafp-1 and/or dafp-4, from the freeze-avoiding insect, Dendroides canadensis, were transferred to Drosophila melanogaster via P-element-mediated transformation. The Northern and Western blots showed expression of DAFP(s) at both transcript and protein levels. The highest thermal hysteresis activity of 6.78+/-0.12 degrees C was detected in 5-day adult flies containing two copies of each of the dafp-1 and dafp-4 genes, while flies with two copies of either dafp-1 or dafp-4 had less activity, 5.52 and 3.24 degrees C, respectively (measured by nanoliter osmometer). This suggests synergistic enhancement of thermal hysteresis activity between DAFP-1 and DAFP-4 in transgenic D. melanogaster containing both DAFPs. Supercooling points without ice in contact with the insects were lowered in all 5 transgenic lines compared with controls, however, when ice was in contact with the flies, supercooling points were lowered only in the heterozygous <DAFP-1>+<DAFP-4> transgenic line. Also, transgenic D. melanogaster exhibited higher survivorship compared with controls when placed at low non-freezing temperatures (0 and 4 degrees C), however, DAFP-1 and DAFP-4 did not display any synergistic enhancement in these non-freezing survival experiments.

Cloning of fish enzymes and other fish protein genes

Fish metabolism needs special enzymes that have maximum activity at very different conditions than their mammalian counterparts. Due to the differences in activity, these enzymes, especially cold-adapted proteases, could be used advantageously for the production of some foods. In addition to the enzymes, this review describes some other unique fish polypeptides such as antifreeze proteins, fluorescent proteins, antitumor peptides, antibiotics, and hormones, that have already been cloned and used in food processing, genetic engineering, medicine, and aquaculture. Recombinant DNA technology, which allows these biological molecules to be cloned and overexpressed in microorganisms is also described, highlighting innovative applications. The expected impact of cloning fish proteins in different fields of technology is discussed.

Expression of a cystine-rich fish antifreeze in transgenic Drosophila melanogaster

We have used Drosophila melanogaster as a model system for the transgenic expression of cystine-rich Type II antifreeze protein (AFP) from sea raven. This protein was synthesized and secreted into fly haemolymph where it migrated as a larger species (16 kDa) than the mature form of the protein (14 kDa) as judged by immunoblotting. Drosophila-produced Type II AFP demonstrated antifreeze activity both in terms of thermal hysteresis (0.13 degree C) and inhibition of ice recrystallization. Recombinant AFP was purified and N-terminal sequencing revealed a 17 aa extension that began at the predicted signal peptide cleavage point. The expression of all three AFP types in transgenic Drosophila has now been achieved. We conclude that the globular Type II and Type III AFPs are better choices for antifreeze transfer to other organisms than is the more widely used linear Type I AFP.

Low temperature persistence of type I antifreeze protein is mediated by cold-specific mRNA stability

In winter flounder, the levels of type I antifreeze protein (AFP) and its mRNA vary seasonally by as much as 1000-fold. Elevated levels in the fall are prompted by the loss of long day-lengths, while higher spring temperatures correlate with AFP clearance. We have investigated the role of temperature on AFP accumulation using transgenic Drosophila melanogaster by expressing multiple AFP genes under control of the heat-inducible hsp70 promoter. AFP and AFP mRNA persisted far longer in flies reared at 10 degrees C compared to 22 degrees C. This difference appears to be mediated by cold-specific mRNA stability since no such temperature effect was observed with either an endogenous heat-inducible mRNA or a constitutively expressed mRNA.

Antifreeze proteins and their potential use in frozen foods

Antifreeze proteins (AFPs) are proteins that have the ability to modify the growth of ice, resulting in the stabilization of ice crystals over a defined temperature range and in the inhibition of the recrystallization of ice. AFPs are found in a wide range of organisms, including bacteria, fungi, plants, invertebrates and fish. Moreover, multiple forms of AFPs are synthesized within each organism. As a result, it should be possible to select an AFP with appropriate characteristics and a suitable level of activity for a particular food product. Antifreeze proteins may improve the quality of foods that are eaten while frozen by inhibiting recrystallization and maintaining a smooth texture. In foods that are frozen only for preservation, AFPs may inhibit recrystallization during freezing, storage, transport and thawing, thus preserving food texture by reducing cellular damage and also minimizing the loss of nutrients by reducing drip. Antifreeze proteins are naturally present in many foods consumed as part of the human diet. However, AFPs may be introduced into other food products either by physical processes, such as mixing and soaking, or by gene transfer.

Isolation and characterization of an antifreeze protein precursor from transgenic Drosophila: evidence for partial processing

Transgenic Drosophila melanogaster that contain a winter flounder antifreeze protein (AFP) gene fused to the transcriptional and translational control sequences of the host heat shock protein 70 gene express the transgene under heat shock conditions. They secrete into the hemolymph small quantities of a protein that reacts with antisera to AFP and is of a similar size to the proAFP precursor. To facilitate purification and characterization of this precursor, transformed fly lines homozygous for inserts on the 2nd, 3rd and X chromosomes were crossed together to generate a line with five and six AFP genes present in males and females, respectively. AFP production in the multi-gene line was approximately equal to the sum of that observed in the three starting lines and was just sufficient to perturb the growth of ice crystals. The AFP component was purified from heat-denatured hemolymph of this line by cation- and anion-exchange chromatography, followed by reverse-phase HPLC. Edman degradation sequencing of the purified protein showed that its N-terminus began two amino acids in from the predicted signal peptide cleavage point. An additional amino acid sequence was present that began two amino acids further into the 'pro' sequence. These AFP products are consistent with processing of the proAFP in Drosophila by a type IV dipeptidyl aminopeptidase, as has been suggested for processing in flounder.