Evolution of pseudogenes in the immunoglobulin V H-gene family of the mouse

A quantitative analysis of the complexity of the J558 V _H -gene family in the mouse immunoglobulin heavy chain (Igh) gene locus has been performed. Considerable variations in the degree of complexity are observed in various Igh haplotypes derived from laboratory mice and wild mice. The BALB/c strain shows the highest degree of complexity of the J558 V _H -gene family when all mice are compared. Multiple gene duplications seem to have occurred in the BALB/c-derived J558 V_H-gene family less than 1–2 million years ago. This dating is supported by the divergence in coding and flanking regions of three strongly homologous V _H -region genes. Two of these genes were generated by the duplication of a pseudogene about 1.5 × 10⁵ years ago. A recent expansion of the J558 V _H -gene family and therefore little time for evolutionary drift may explain why most of the pseudogenes in this family exhibit a largely intact structure. We also describe two V _H -region genes which represent older pseudogenes in states of progressive disintegration.     

Phylogenetic distribution in the genus Mus of t-complex-specific DNA and protein markers: inferences on the origin of t-haplotypes

We have examined the phylogenetic distribution of two t-specific markers among representatives of various taxa belonging to the genus Mus. The centromeric TCP-1a marker (a testicular protein variant specific for all t-haplotypes so far studied) has also been apparently detected in several non-t representatives of the Mus IVA, Mus IVB, and probably M. cervicolor species. By contrast, a t-specific restriction- fragment-length polymorphism allele (RFLP) of the telomeric alpha- globin pseudogene DNA marker alpha-psi-4 was found only in animals belonging to the M. musculus-complex species either bearing genuine t- haplotypes or, like the M. m. bactrianus specimen studied here, likely to do so. This t-specific alpha-psi-4 RFLP allele was found to be as divergent from the RFLP alleles of the latter, non-t, taxonomical groups as it is from Mus 4A, Mus 4B, or M. spretus ones. These results suggest the presence of t-haplotypes and of t-specific markers in populations other than those belonging to the M. m. domesticus and M. m. musculus subspecies, implying a possible origin for t-haplotypes prior to the radiation of the most recent offshoot of the Mus genus (i.e., the spretus/domesticus divergence), some 1-3 Myr ago.      

A theoretical analysis of radiation interception in a two-species plant canopy.

Classical radiation interception laws for monospecific canopies cannot be used directly for bispecific canopies. They are always based on the gap frequency concept (i.e., the probability of no interception), which does not provide any information about the sharing of intercepted radiation between species. A theoretical analysis is reported that relates the radiation interception probabilities to the geometrical structure of the crop (i.e., the leaf area density and the leaf angle distribution of each component) and the foliage dispersion. The leaf dispersion globally describes the spatial relations between the leaf elements; it may be regular if the leaves avoid mutual shading, random, or clumped if they tend to overlap. For such two-species canopies, the leaf dispersions within each component (WSLD: within-species leaf dispersion) and between two species (BSLD: between-species leaf dispersion) are distinguished. Using bivariate multinomial distributions, general expressions for the gap frequency and the interception probabilities of a homogeneous vegetation layer were set as exponential functions of the foliage thickness, taking into account a number of dispersion parameters as small as possible. First, one WSLD for each species describes the rate of foliage overlap between the leaves of this species; it is quite similar to the leaf dispersion of single-species canopies. Second, the rate of foliage overlap between species is characterized by one BSLD. As in monospecific canopies, this parameter is positive, zero, or negative, respectively, for regular, random, or clumped BSLD. Third, another BSLD parameter has to be used if the foliage overlap between species is more than random (i.e., in the case of clumped BSLD); the latter shows the direction of overlap between species and may be taken as the probability of finding a leaf element of the first species in the case of marked overlapping. Suggestions for estimating the leaf dispersion parameters and possible uses of such relations are also discussed.     

H-2 Polymorphisms Are More Uniformly Distributed than Allozyme Polymorphisms in Natural Populations of House Mice

Patterns of H-2 and allozyme polymorphism in natural populations of house mice from Europe, North Africa and South America were analyzed. The purpose of the analysis was to determine whether H-2 and allozyme polymorphisms were similarly distributed both geographically and temporally in wild mice. Two subspecies of house mice, Mus musculus domesticus and M. m. musculus were sampled and the polymorphisms of two H-2 class I genes, H-2K and H-2D, and 34 allozyme-encoding genes were surveyed. The three kinds of analyses that were conducted included a hierarchical gene diversity analysis, an analysis of the effects of barriers to gene flow, and an analysis of similarity networks. Each of the comparisons demonstrated that H-2 polymorphisms were more uniformly distributed than allozyme polymorphisms and provided additional evidence that H-2 and allozyme polymorphisms are subject to different evolutionary pressures. The analysis of similarity networks also demonstrated that H-2 genes provide little information about the phylogeny of wild mice.     

Serological survey of T-lymphocyte differentiation antigens in wild mice

Allelic distributions of Thy-1, Ly-l, and Ly-2 antigens in wild mice are characteristic of each Mus musculus subspecies. Eastern mice (M.m.molossinus, M.mmusculus, M.m.castaneus, M.m.bactrianus) express the Thy-1.1 antigen, whereas Western mice (M.m. domesticus, M.m.brevirostris) express the Thy-1.2. All mice from wild populations examined in this survey express the Ly-1.2. The Ly-2.1 is distributed in Eastern mice and some Western mice, and the Ly-2.2 is found in the remaining Western mice. Allelic distributions of these antigens were also examined in two other species, Mus spretus and Mus spicilegus. Allelic constitutions of Thy-1 and Ly-1 in these species are similar to those of Eastern mice. Some M.spicilegus, however, express the Ly-1.1 antigen. This antigenic type is not found in M.musculus. Some Eastern mice related to M.m.castaneus react weakly to Ly-1.2-specific and Ly-2.1-specific monoclonal antibodies in both the complement-mediated cytotoxicity test and the absorption test. These results suggest that M.m.castaneus has unique alleles in the Ly-1 and Ly-2 loci.     

Increase in nuclear aluminum concentration during hepatic regeneration: study by analytical ionic microscopy

20 hrs. after partial hepatectomy, a significant increase in the aluminum concentration of liver cell nuclei has been measured by analytical ion microscopy. These results indicate a possible role of aluminium in an in vivo induced proliferative response.     

Counterselection on sex chromosomes in the Mus musculus European hybrid zone

The extent to which alleles can disperse across a hybrid zone depends on the selection they are subjected to in the hybrid genetic background or, for those that are selectively neutral, on their ability to escape from the unfavourable environment by recombination. Three markers spanning a 45 cM segment in the center of the X chromosome were used to investigate the degree to which selection against X chromosome linked genes helps to maintain the barrier to gene flow in the hybrid zone between Mus musculus domesticus and M. m. musculus in Denmark. The introgression of all the sex chromosome specific markers was more limited than that of the autosomal enzymes (Idh1, Amy, Gpd1, Pgm1, Es1, Es2, Mpi, Np1, Es10, Sod1) and the mitochondrial DNA. The cline for DXPas2, which is in the center of the X chromosome, is extremely steep and shows that certain genes located in this region are strongly selected against in the hybrid background. The clines of the other two X-linked markers, Hprt and DXPas1, and of the Y chromosome are not as abrupt and all three have similar asymmetric introgression patterns. Although the musculus variants appear to behave in much the same way as those of the autosomal genes, the domesticus variants do not introgress. The results show that X-linked and to a lesser extent Y-linked genes are more strongly selected against in the hybrid genome than the mitochondrial genome or the different autosomal loci. This suggests that co-adapted gene systems involving the sex chromosomes may play an important role in the hybrid breakdown between the two subspecies.