Rapid evolution of a young L1 (LINE-1) clade in recently speciated rattus taxa

L1 elements are retrotransposons that have been replicating and evolving in mammalian genomes since before the mammalian radiation. Rattus norvegicus shares the young L1_mlvi2 clade only with its sister taxon, Rattus cf moluccarius. Here we compared the L1_mlvi2 clade in these recently diverged species and found that it evolved rapidly into closely related but distinct clades: the L1_mlvi2-rm clade (or subfamily), characterized here from R. cf moluccarius, and the L1_mlvi2-rn clade, originally described in R. norvegicus. In addition to other differences, these clades are distinguished by a cluster of amino acid replacement substitutions in ORF I. Both rat species contain the L1_mlvi2-rm clade, but the L1_mlvi2-rn clade is restricted to R. norvegicus. Therefore, the L1_mlvi2-rm clade arose prior to the divergence of R. norvegicus and R. cf moluccarius, and the L1_mlvi2-rn clade amplified after their divergence. The total number of L1_mlvi2-rm elements in R. cf moluccarius is about the same as the sum of the L1_mlvi2-rm and L1_mlvi2-rn elements in R. norvegicus. The possibility that L1 amplification is in some way limited so that the two clades compete for replicative supremacy as well as the implications of the other distinguishing characteristic of the L1_mlvi2-rn and L1_mlvi2-rm clades are discussed. Received: 6 November 1996 / Accepted: 12 April 1997     

Protein tyrosine phosphatase-1C is rapidly phosphorylated in tyrosine in macrophages in response to colony stimulating factor-1.

An approximately 64-kDa cytoplasmic protein is rapidly phosphorylated in tyrosine in the response of macrophages to colony stimulating factor-1. To identify this protein, BAC1.2F5 macrophages were incubated with or without colony stimulating factor-1, the phosphotyrosine-containing portion of their cytosolic fractions subjected to size exclusion chromatography, and the 45-70-kDa fraction further fractionated by reverse phase high pressure liquid chromatography (RP-HPLC). Tryptic peptides of pooled RP-HPLC fractions from stimulated cells (containing the approximately 64-kDa protein and an approximately 54-kDa protein) and from unstimulated cells (containing the approximately 54-kDa protein alone), were sequenced directly. All seven readable sequences of 8 sequenceable peptides present uniquely in the stimulated fraction were present in the sequence of the src homology 2 domain-containing protein tyrosine phosphatase-1C (PTP-1C). The identity of the approximately 64-kDa protein was confirmed by Western blotting with an antibody raised to a PTP-1C peptide. The rapid, growth factor-induced tyrosine phosphorylation of PTP-1C suggests that it may be involved in very early events in growth factor signal transduction.     

Genetic diversity of the killifish Aphanius fasciatus paralleling the environmental changes of Tarquinia salterns habitat

The habitat in the Natural Reserve of the Tarquinia salterns, located on the Tyrrhenian coast of central Italy, has undergone dramatic alterations over the last 10 years. After salt production was terminated in 1997 the site was abandoned until 2002, with consequent degradation of habitat quality and stiffening of the environmental conditions. From 2003 to 2006 ecological rehabilitation of the site was carried out, restoring water circulation to its previous equilibrium. The genetic variation in the killifish Aphanius fasciatus inhabiting the salterns was monitored using allozymes from 1998. The results showed that the genetic variability of the killifish strongly reduced through time: a high number of rare alleles were lost and both heterozygosity and allele richness were significantly decreased. The most recent samples, taken after the ecological restoration, showed that to date the genetic erosion of A. fasciatus gene pool has slowed down, since no significant differences have been detected for any genetic variability parameter. Concerning the mechanisms leading to the impoverishment of the genetic variability, the strong loss of rare alleles suggests a role of genetic drift, which accords with the fluctuation of the effective population size recorded over the period of study and with the low gene flow typical of this species. The low levels of gene flow reported for this species imply that once lost, the genetic variability can rarely be restored through immigration from highly variable populations.