An embryogenic cell line of maize from A188 (Minnesota) contains Mu1-like elements

The maize inbred line A188 is popularly used for the production of embryogenic cell lines. A188, maintained at the University of Minnesota, was found upon molecular analysis to contain 2 to 4 copies of a DNA sequence very similar in structure to transposable Mu1 elements, which have been implicated in Robertson's Mutator system. These Mu1-like elements are in the same chromosomal locations in sibling plants and in A188 cell cultures derived from them. This suggests that the elements are in an inactive state and do not undergo transposition. However, we have observed that they are not modified at the target sites for certain restriction endonucleases. Possible causes for the apparent lack of transposition of these Mu1-like elements in these A188 lines are discussed. Inasmuch as the elements do not transpose, they must be maintained in this line as homozygous Mendelian elements by self-pollination.Journal paper no. J-12269 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa 50011. Project 2707.     

Methods for computing the standard errors of branching points in an evolutionary tree and their application to molecular data from humans and apes

Statistical methods for computing the standard errors of the branching points of an evolutionary tree are developed. These methods are for the unweighted pair-group method-determined (UPGMA) trees reconstructed from molecular data such as amino acid sequences, nucleotide sequences, restriction-sites data, and electrophoretic distances. They were applied to data for the human, chimpanzee, gorilla, orangutan, and gibbon species. Among the four different sets of data used, DNA sequences for an 895-nucleotide segment of mitochondrial DNA (Brown et al. 1982) gave the most reliable tree, whereas electrophoretic data (Bruce and Ayala 1979) gave the least reliable one. The DNA sequence data suggested that the chimpanzee is the closest and that the gorilla is the next closest to the human species. The orangutan and gibbon are more distantly related to man than is the gorilla. This topology of the tree is in agreement with that for the tree obtained from chromosomal studies and DNA-hybridization experiments. However, the difference between the branching point for the human and the chimpanzee species and that for the gorilla species and the human-chimpanzee group is not statistically significant. In addition to this analysis, various factors that affect the accuracy of an estimated tree are discussed.      

β-Oxidation enzymes in the mitochondria of Arum and oilseed rape

-Oxidation enzymes were detected both in the mitochondria and microbodies of Arum maculatum L. spadices and Brassica napus L. seeds. It is apparent that the mitochondrial membrane barrier, which remains intact after sucrose-density-gradient centrifugation, prevents rapid access of acyl-GoA substrates to matrix oxidation tes. Thus intact mitochondria showed little -oxidation enzyme activity. Rupturing of the mitochondrial membrane allowed rapid access of acyl CoAs to matrix sites. Consequently, in ruptured mitochondria, high -oxidation enzyme activities were measured.C. Masterson thanks the Science and Engineering Research Council for the award of a postgraduate student maintenance grant. D.R. Thomas and C. Wood thank their relatives for continuing financial support. The authors also thank West Cumberland Farmers Ltd., Hexham, UK for their gift of oilseed rape seeds.     

Mesodern-inducing factors and mesodermal patterning

Identification of the signalling molecules involved in mesoderm formation in amphibian embryos still presents problems. None of the original candidates, such as activin, have been definitively ruled out, and the new factors, such as the nodal-related genes, have come on to the scene. Of the original candidates, activin has been definitively shown to act as a morphogen, whereas bone morphogenetic protein (BMP)-4 has emerged as a ventral inducer and an inhibitor of neural differentiation. The effects of BMP-4 are antagonized by chordin, a molecule related to the product of the Drosophila gene short gastrulation.     

Ant genomics sheds light on the molecular regulation of social organization

Ants are powerful model systems for the study of cooperation and sociality. In this review, we discuss how recent advances in ant genomics have contributed to our understanding of the evolution and organization of insect societies at the molecular level.     

Did the prion protein become vulnerable to misfolding after an evolutionary divide and conquer event?

Despite high sequence identity among mammalian prion proteins (PrPs), mammals have varying rates of susceptibility to prion disease resulting in a so-called species barrier. The species barrier follows no clear pattern, with closely related species or similar sequences being no more likely to infect each other, and remains an unresolved enigma. Variation of the conformationally flexible regions may alter the thermodynamics of the conformational change, commonly referred to as the conformational conversion, which occurs in the pathogenic process of the mammalian prion protein. A conformational ensemble scenario is supported by the species barrier in prion disease and evidence that there are strains of pathogenic prion with different conformations within species. To study how conformational flexibility has evolved in the prion protein, an investigation was undertaken on the evolutionary dynamics of structurally disordered regions in the mammalian prion protein, non-mammalian prion protein that is not vulnerable to prion disease, and remote homologs Doppel and Shadoo. Structural disorder prediction analyzed in an evolutionary context revealed that the occurrence of increased or altered conformational flexibility in mammalian PrPs coincides with key events among PrP, Doppel, and Shadoo. Comparatively rapid evolutionary dynamics of conformational flexibility in the prion protein suggest that the species barrier is not a static phenomenon. A small number of amino acid substitutions can repopulate the conformational ensemble and have a disproportionately large effect on pathogenesis.