Testing the role of phenotypic plasticity for local adaptation: growth and development in time-constrained Rana temporaria populations.

Phenotypic plasticity can be important for local adaptation, because it enables individuals to survive in a novel environment until genetic changes have been accumulated by genetic accommodation. By analysing the relationship between development rate and growth rate, it can be determined whether plasticity in life-history traits is caused by changed physiology or behaviour. We extended this to examine whether plasticity had been aiding local adaptation, by investigating whether the plastic response had been fixed in locally adapted populations. Tadpoles from island populations of Rana temporaria, locally adapted to different pool-drying regimes, were monitored in a common garden. Individual differences in development rate were caused by different foraging efficiency. However, developmental plasticity was physiologically mediated by trading off growth against development rate. Surprisingly, plasticity has not aided local adaptation to time-stressed environments, because local adaptation was not caused by genetic assimilation but on selection on the standing genetic variation in development time.

Drosophila ferritin mRNA: alternative RNA splicing regulates the presence of the iron-responsive element.

Several mRNAs encoding the same ferritin subunit of Drosophila melanogaster were identified. Alternative RNA splicing and utilisation of different polyadenylation sites were found to generate the transcripts. The alternative RNA splicing results in ferritin transcripts with four unique 5' untranslated regions. Only one of them contains an iron-responsive element. The iron-responsive element was found to bind in vitro specifically to human recombinant iron regulatory protein 1. Furthermore, the ferritin subunit mRNAs are differentially expressed during development. Our data provides the first molecular evidence that the presence of iron-responsive element in a ferritin mRNA is regulated by alternative RNA splicing.

An atypical iron-responsive element (IRE) within crayfish ferritin mRNA and an iron regulatory protein 1 (IRP1)-like protein from crayfish hepatopancreas.

A putative crayfish iron-responsive element (IRE) is present in the 5'-untranslated region of the crayfish ferritin mRNA. The putative crayfish IRE is in a cap-proximal position and shares most of the structural features of the consensus IRE, but the RNA stem-loop structure contains a bulge of a guanine instead of a cytosine at the expected position, so far thought to be a hallmark of IREs. By using an electromobility shift assay this IRE was shown to specifically bind purified recombinant human iron regulatory protein 1 (IRP1) as well as a factor(s) present in a homogenate of crayfish hepatopancreas, likely to be a crayfish IRP1 homologue. With mutations in the crayfish IRE, the affinity of IRP to IRE was drastically decreased. A cDNA encoding an IRP1-like protein was cloned from the hepatopancreas of crayfish. This protein has sequence similarities to IRP, and contains all the active-site residues of aconitase, two putative RNA-binding regions and a putative contact site between RNA and IRP. These results show that a crayfish IRE, lacking the bulged C, can bind IRP1 in vitro and that an IRP1-like protein present in crayfish hepatopancreas may have both aconitase and RNA-binding activities.

The degree of adaptive phenotypic plasticity is correlated with the spatial environmental heterogeneity experienced by island populations of Rana temporaria.

Although theoretical models have identified environmental heterogeneity as a prerequisite for the evolution of adaptive plasticity, this relationship has not yet been demonstrated experimentally. Because of pool desiccation risk, adaptation of development rate is important for many amphibians. In a simulated pool-drying experiment, we compared the development time and phenotypic plasticity in development time of populations of the common frog Rana temporaria, originating from 14 neighbouring islands off the coast of northern Sweden. Drying regime of pools used by frogs for breeding differed within and among the islands. We found that the degree of phenotypic plasticity in development time was positively correlated with the spatial variation in the pool-drying regimes present on each island. In addition, local adaptation in development time to the mean drying rate of the pools on each island was found. Hence, our study demonstrates the connection between environmental heterogeneity and developmental plasticity at the island population level, and also highlights the importance of the interplay between local specialization and phenotypic plasticity depending on the local selection pressures.

Peroxinectin, a novel cell adhesion protein from crayfish blood.

From blood cells of the crayfish Pacifastacus leniusculus a 76-kDa protein that mediated attachment and spreading of the crayfish blood cells was purified. The cDNA for this cell adhesion protein was isolated, cloned, and sequenced. The deduced protein sequence was significantly similar to one family of peroxidases, e.g., myeloperoxidase. Consistently, the 76-kDa protein, for which we propose the name peroxinectin, had peroxidase activity. A synthetic peptide derived from the peroxinectin sequence containing Lys-Gly-Asp mimicked the cellular activity of the intact protein, implicating this sequence as the cell-binding site. Peroxinectin is the first cell adhesion molecule cloned from invertebrate blood and, to our knowledge, the first protein from any organism that combines being a cell adhesion ligand and a peroxidase.

Using PRINS for gene mapping in polytene chromosomes.

We have adapted the primed in situ labelling (PRINS) protocol for gene mapping in polytene chromosomes of two dipteran species. The method was used to localize the genes for the Balbiani ring (BR) 2.1 and the iron-regulatory protein 1A (IRP1A) in polytene salivary gland chromosomes of Chironomus tentans, and Drosophila melanogaster respectively. Two oligonucleotides, corresponding to the BR 2.1 and IRP1A genes, were used as primers and the whole procedure was performed within 3-4 h. The strong labelling with low background revealed the localization of the BR 2.1 gene in polytene chromosome IV of C. tentans and the IRP1A gene in polytene chromosome 3R83 of D. melanogaster. The results demonstrated that PRINS is a fast, sensitive and suitable approach for physical gene mapping in polytene chromosomes.