Natural killer cells in the thymus. Studies in mice with severe combined immune deficiency

The relationship between NK cell and T cell progenitors was investigated by using mice with severe combined immune deficiency (scid). Scid mice are devoid of mature T and B cells because they cannot rearrange their Ig and TCR genes. However, they have normal splenic NK cells. Thymus of scid mice, although markedly hypocellular, contains cells that lyse YAC-1, an NK-sensitive tumor cell. By flow cytometry, two populations of cells were identified in the scid thymus. Eighty percent of the cells were Thy-1+, IL-2R(7D4)+, J11d+, CD3-, CD4-, CD8- whereas the remaining were IL-2R-, J11d-, CD3-, CD4-, and CD8-. By cell sorting, all NK activity was found in the latter population, which is phenotypically similar to splenic NK cells. To determine if the thymus contains a bipotential NK/T progenitor cell, J11d+, IL-2R+ cells were cultured and analyzed for the generation of NK cells in vitro. These cells were used because they resemble 15-day fetal and adult CD4- CD8- thymocytes that are capable of giving rise to mature T cells. Cultured J11d+ thymocytes acquired non-MHC-restricted cytotoxicity, but in contrast to mature NK cells, the resulting cells contained mRNA for the gamma, delta, and epsilon-chains of CD3. This suggests that J11d+ cells are early T cells that can acquire the ability to kill in a non-MHC-restricted manner, but which do not give rise to NK cells in vitro. The differentiative potential of scid thymocytes was also tested in vivo. Unlike bone marrow cells, scid thymocytes containing 80% J11d+ cells failed to give rise to NK cells when transferred into irradiated recipients. Together these results suggest that mature NK cells reside in the thymus of scid mice but are not derived from a common NK/T progenitor.     

BCR sequences essential for transformation by the BCR-ABL oncogene bind to the ABL SH2 regulatory domain in a non-phosphotyrosine-dependent manner.

BCR-ABL is a chimeric oncogene implicated in the pathogenesis of Philadelphia chromosome-positive human leukemias. BCR first exon sequences specifically activate the tyrosine kinase and transforming potential of BCR-ABL. We have tested the hypothesis that activation of BCR-ABL may involve direct interaction between BCR sequences and the tyrosine kinase regulatory domains of ABL. Full-length c-BCR as well as BCR sequences retained in BCR-ABL bind specifically to the SH2 domain of ABL. The binding domain has been localized within the first exon of BCR and consists of at least two SH2-binding sites. This domain is essential for BCR-ABL-mediated transformation. Phosphoserine/phosphothreonine but not phosphotyrosine residues on BCR are required for interaction with the ABL SH2 domain. These findings extend the range of potential SH2-protein interactions in growth control pathways and suggest a function for SH2 domains in the activation of the BCR-ABL oncogene as well as a role for BCR in cellular signaling pathways.     

Changes in the Frequency Structure of a Mating Call Decrease Its Attractiveness to Females in the Cricket Frog Acris crepitans blanchardi

In many species, females often prefer male signals that are more complex than in nature or beyond the range of calls naturally produced by conspecific males in spectral, temporal and amplitude features. In this study we examined both the ability of females to recognize signals outside the normal range of spectral frequency variation seen in male advertisement calls, and the influence of increasing call complexity by adding spectral components to enhance the attractiveness of a male advertisement call in the cricket frog Acris crepitans blanchardi, while keeping its amplitude constant. We used two different natural male call groups and created the following synthetic call groups: with a dominant frequency at 3500 Hz, i.e. at the normal dominant frequency with a frequency band within the sensitivity range of the inner ear basilar papilla; with a dominant frequency at 700 Hz, i.e. outside the normal range of variation and with a frequency band outside the sensitivity range of the basilar papilla but within the range of the amphibian papilla; with two dominant frequencies, one at 700 Hz and another at 3500 Hz, stimulating the basilar and amphibian papilla simultaneously. In double choice experiments we tested all combinations of the three call groups, and we tested the 3500 Hz call groups against the same natural call groups. Additionally, we tested the 700 Hz call groups against white noise to see whether these signals are meaningful in mate choice. Females preferred 3500 Hz call groups over all other call groups. The synthetic call group was as attractive to females as the same natural call group. The 700 Hz call group was not meaningful in mate choice. The combined (700 Hz + 3500 Hz) call group was significantly less attractive to females than the 3500 Hz call group. Thus, making a call more spectrally complex without increasing its overall amplitude decreases its attractiveness to cricket frog females.     

The genetic basis of phenotypic convergence in beach mice: similar pigment patterns but different genes

Convergent evolution is a widespread phenomenon seen in diverseorganisms inhabiting similar selective environments. However,it is unclear if similar phenotypes are produced by the sameor different genes and mutations. Here we analyze the molecularmechanisms underlying convergent pigment pattern among subspeciesof the beach mouse (Peromyscus polionotus) inhabiting the Gulfand Atlantic coasts of Florida. In these two geographic regions,separated by more than 300 km, "beach mice" have lighter coloredcoats than do their mainland counterparts, produced by naturalselection for camouflage against the pale coastal sand dunes.We measured color pattern in eight beach mouse subspecies andshowed that three of the Gulf Coast subspecies are more phenotypicallysimilar to an Atlantic coast subspecies than to their Gulf Coastneighbors. However, light-colored beach mice do not form a monophyleticgroup. Previous results implicated a single derived amino acidchange in the melanocortin-1 receptor (Mc1r) as a major contributorto pigment pattern in the Gulf Coast beach mice; despite phenotypicsimilarities, the derived Mc1r allele was not found in the Atlanticcoast beach mouse populations. Here we show that Atlantic coastbeach mice have high levels of Mc1r polymorphism but they lackunique alleles. Functional assays revealed that single aminoacid mutations segregating in Atlantic coast beach mice do notcause any change in Mc1r activity compared with the activityof Mc1r from dark-colored mice. These joint results show thatconvergent pigment patterns in recently diverged beach mousesubspecies—whose developmental constraints are presumablysimilar—have evolved through a diversity of genetic mechanisms.     

Phylogeny of Eunicida (Annelida) and exploring data congruence using a partition addition bootstrap alteration (PABA) approach

Even though relationships within Annelida are poorly understood, Eunicida is one of only a few major annelid lineages well supported by morphology. The seven recognized eunicid families possess sclerotized jaws that include mandibles and a maxillary apparatus. The maxillary apparatuses vary in shape and number of elements, and three main types are recognized in extant taxa: ctenognath, labidognath, and prionognath. Ctenognath jaws are usually considered to represent the plesiomorphic state of Eunicida, whereas taxa with labidognath and prionognath are thought to form a derived monophyletic assemblage. However, this hypothesis has never been tested in a statistical framework even though it holds considerable importance for understanding annelid phylogeny and possibly lophotrochozoan evolution because Eunicida has the best annelid fossil record. Therefore, we used maximum likelihood and Bayesian inference approaches to reconstruct Eunicida phylogeny using sequence data from nuclear 18S and 28S rDNA genes and mitochondrial 16S rDNA and cytochrome c oxidase subunit I genes. Additionally, we conducted three different tests to investigate suitability of combining data sets. Incongruence length difference (ILD) and Shimodaira-Hasegawa (SH) test comparisons of resultant trees under different data partitions have been widely used previously but do not give a good indication as to which nodes may be causing the conflict. Thus, we developed a partition addition bootstrap alteration (PABA) approach that evaluates congruence or conflict for any given node by determining how bootstrap scores are altered when different data partitions are added. PABA shows the contribution of each partition to the phylogeny obtained in the combined analysis. Generally, the ILD test performed worse than the other approaches in detecting incongruence. Both PABA and the SH approach indicated the 28S and COI data sets add conflicting signal, but PABA is more informative for elucidating which data partition may be misleading at a given node. All our analyses indicate that the monophyly of the labidognath/prionognath taxa and even a labidognath clade (i.e., a "Eunicidae"/Onuphidae/Lumbrineridae clade) is significantly rejected. We show that the definition of both the labidognath and ctenognath jaw type does not address adequately the variation within Eunicida and thus misleads our current evolutionary understanding. Based on the presented results a symmetric maxillary apparatus with a carrier and four to six maxillae is most likely the plesiomorphic condition for Eunicida. [COI; conflicting data; fossil record; ILD; Jaw Evolution; molecular phylogeny; rDNA; SH test.].     

Isoaspartate-containing amyloid precursor protein-derived peptides alter efficacy and specificity of potential beta-secretases

Neuritic plaques of Alzheimer patients are composed of multiple protein components. Among them, the amyloid beta-peptides (Abeta) 1-40/42 and further N- and C-terminally modified fragments of Abeta are highly abundant. Most prominent are the isoaspartate (isoAsp)-Abeta peptides and pyroglutamyl (pGlu)-Abeta. While pGlu-Abeta can only be formed from an N-terminal glutamate by glutaminyl cyclase, spontaneous isoAsp-isomerization cannot occur at an N-terminal aspartate of peptides. This means that isoAsp-Abeta formation must precede proteolysis of the amyloid precursor protein (APP). Abeta generation from APP by beta- and gamma-secretases initiates the amyloid peptide aggregation and deposition process. Two aspartate proteases have been identified as secretases: BACE-1 (beta-site amyloid precursor protein cleaving enzyme) and the intramembrane gamma-secretase multiprotein complex. However, recent evidence supports more than one beta-secretase initiating this cascade. Formation of Abeta1-40/42 was predominantly studied by expression of mutated human APP sequences in cell culture and transgenic animals, generating Abeta fragments that did not contain such multiple posttranslational modifications as in Alzheimer's disease. This prompted us to investigate the catalytic turnover of Asp- or isoAsp-containing APP-derived peptide sequences by BACE-1 and cathepsin B, another potential beta-secretase. While cathepsin B is more effective than BACE-1 in processing the Asp-containing peptide derivatives, only cathepsin B can cleave the isoAsp-containing peptides, which occurs with high catalytic efficiency.     

Two reciprocally monophyletic mtDNA lineages elucidate the taxonomic status of Mountain gazelles (Gazella gazella)

Mountain gazelles (Gazella gazella) rank among the most critically endangered mammals on the Arabian Peninsula. Past conservation efforts have been plagued by confusion about the phylogenetic relationship among various ‘phenotypically discernable’ populations, and even the question of species boundaries was far from being certain. This lack of knowledge has had a direct impact on conservation measures, especially ex situ breeding programmes, hampering the assignment of captive stocks to potential conservation units. Here, we provide a phylogenetic framework, based on the analysis of mtDNA sequences (360 bp cytochrome b and 213 bp Control Region) of 126 individuals collected from the wild throughout the Arabian Peninsula and from captive stocks. Our analyses revealed two reciprocally monophyletic genetic lineages within the presumed species Gazella gazella: one ‘northern clade’ on the Golan Heights (Israel/Syrian border) and one genetically diverse larger clade from the rest of the Arabian Peninsula including the Arava Valley (Negev, Israel). Applying the Strict Phylogenetic Species Concept (sensu Mishler & Theriot, 2000 Mishler, B. D. and Theriot, E. C. 2000. “The phylogenetic species concept (sensu Mishler and Theriot): monophyly, apomorphy, and phylogenetic species concepts”. In Species Concepts and Phylogenetic Theory. A Debate, Edited by: Wheeler, Q. D. and Meier, R. 44–54. Columbia University Press, NY.  [Google Scholar]) allows assigning species status to these two major clades.