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Biochemical Genetics (v.38, #5-6)
A Single Genetic Determinant that Prevents Sex Reversal in C57BL-YPOS Congenic Mice by J. Barry Whitney III; Thomas M. Mills; Ronald W. Lewis; Roger Wartell; Tom O. Abney (pp. 119-137).
Sex determination in the mammalian embryo begins with the activation of a gene on the Y chromosome which triggers a cascade of events that lead to male development. The mechanism by which this gene, designated SRY in humans and Sry in mice (sex determining region of the Y chromosome), is activated remains unknown. Likewise, the downstream target genes for Sry remain unidentified at present. C57BL mice carrying a Y chromosome from Mus musculus musculus or molossinus develop normally as males. In contrast, C57BL/6 mice with the Y chromosome from M. m. domesticus often show sex reversal, i.e., develop as XY females. It has been documented that C57BL mice with the Y chromosome from Poschiavinus (YPOS), a domesticus subtype, always develop as females or hermaphrodites. This suggests that a C57BL gene either up- or downstream of Sry is ineffective in interacting with Sry, which then compromises the processes that lead to normal male sex development. Nonetheless, by selective breeding, we have been able to generate a sex reversal-resistant C57BL/6-congenic strain of mice in which the XYPOS individuals consistently develop as normal males with bilateral testes. Because the resistance to sex reversal was transferred from strain 129S1/Sv (nonalbino) by simple selection over 13 backcross generations, it is inferred that a single autosomal gene or chromosomal region confers resistance to the sex reversal that would otherwise result. XYPOS normal males generated in these crosses were compared to XYPOS abnormal individuals and to C57BL/6 controls for sexual phenotype, gonadal weight, serum testosterone, and major urinary protein (MUP) level. A clear correlation was found among phenotypic sex, MUP level, and testis weight in the males and in the incompletely masculinized XYPOS mice. The fully masculinized males of the congenic strain resemble C57BL/6 males in the tested parameters. DNA analysis confirmed that these males, in fact, carry the YPOS Sry gene.
Keywords: sex determination; Sry gene; Y chromosome; sex reversal; mouse genetics; major urinary protein; testosterone.
Allozyme Diversity and Population Genetic Structure of Pinus densata Master in Northwestern Yunnan, China by Hong Yu; Song Ge; De-yuan Hong (pp. 138-146).
We investigated the levels and patterns of genetic diversity of Pinus densata Master in Yunnan. Horizontal starch-gel electrophoresis was performed on macrogametophytes collected from nine populations in northwestern Yunnan, China. Compared with other gymnosperm species, P. densata has higher mean values for all measures of genetic diversity. Allozyme polymorphism (0.99 criterion) was 97.0% and 71.4% at the species and population levels, respectively. The average number of alleles per locus was 3.1 and 2.0 at the species and population levels. Mean expected heterozygosity was substantially higher in P. densata than average values investigated for other gymnosperms both at the population (H ep = 0.174±0.031) and at the species (H es = 0.190) levels. Of the total genetic variation, less than 12% was partitioned among populations (G ST = 0.112). Our allozyme survey supports the suggestion that the observed higher diversity in P. densata may be attributed partly to its hybrid origin between two genetically distinct species, P. yunnanensis and P. tabulaeformis. In addition, we suggest that introgression would give rise to the increase in genetic diversity occurring in P. densata.
Keywords: Pinus densata Master; population; allozymes; diversity; differentiation.
Low Genetic Variation of the Yunnan Hare (Lepus comus G. Allen 1927) as Revealed by Mitochondrial Cytochrome b Gene Sequences
by Chun-Hua Wu; Hai-Peng Li; Ying-Xiang Wang; Ya-Ping Zhang (pp. 147-153).
Identification and Characterization of a cDNA Clone Encoding the Heat Shock Protein (Hsp60) from the Biting Midge, Culicoides variipennis sonorensis Wirth and Jones by M. A. Abdallah; R. S. Pollenz; R. A. Nunamaker; K. E. Murphy (pp. 154-162).
A cDNA expression library constructed from Culicoides variipennis sonorensis was screened using an antibody specific for Hsp60 of Heliothis virescens. A single clone encoding the complete heat shock protein (Hsp60) of C. variipennis was identified and its 2400-bp insert was sequenced. The encoded 62-kDa protein contains 581 amino acids and includes a 26-amino acid putative mitochondrial targeting sequence at its N terminus and a GGM motif at its carboxyl terminus. Deduced amino acid sequences are highly similar (67–78%) to Hsp60 of other species, including the fruit fly, the house mouse, the Norwegian rat, the Chinese hamster, the human, a nematode, and the tobacco budworm moth. This is the initial isolation of a coding sequence for a stress-induced protein in C. variipennis.
Keywords: hsp60; cDNA; Culicoides variipennischaperonin.
Genetic Control of Biogenic-Amine Systems in Drosophila Under Normal and Stress Conditions by Akinori Hirashima; Madina Jh. Sukhanova; Inga Yu. Rauschenbach (pp. 163-176).
The contents of octopamine and its precursors (tyrosine and tyramine) were studied in adults of two lines of Drosophila virilis with contrasting stress responses. It was demonstrated that in individuals responding to stress by a hormonal stress reaction (line 101), the contents of octopamine and tyrosine are lower than in nonresponding flies (line 147). It was found that there is no difference between the lines in the level of tyramine under normal conditions. The dopamine response to stressor was also studied. Genetic analysis of these differences revealed that they are controlled by a single gene and that the gene is not sex-linked. The gene controlling the response was found to be linked to chromosome 6 of D. virilis.
Keywords: octopamine; dopamine; tyrosine; tyramine; Drosophila virilis.
Functional Correlation in Amino Acid Residue Mutations of Yeast Iso-2-Cytochrome c that Is Consistent with the Prediction of the Concomitantly Variable Codon Theory in Cytochrome c Evolution by Alice Fisher; Ying Shi; Alice Ritter; James A. Ferretti; Gloria Perez-Lamboy; Mona Shah; Joseph Shiloach; Hiroshi Taniuchi (pp. 177-196).
Fitch and Markowitz' theory of concomitantly variable codons (covarions) in evolution predicted the existence of functional correlation in amino acid residue mutations among present-day cytochromes c. Mutational analysis was carried out on yeast iso-2-cytochrome c, where hydrophobic core residues I20, M64, L85, and M98 and surface residue L9 were mutated, in selected combinations, to those found in mammalian and bird cytochromes c. The functionality assay is based upon the ability of yeast cells to grow in YPGE medium. Furthermore, experiments on the single M64L and M98L mutations as well as the double M64L/M98L mutation using NMR showed that the effects of these mutations are to perturb the structural integrity of the protein. We identified functional correlation in two cases of a pair of residue mutations, the I20 → V and M98 → L pair and the L9 → I and L85 → I pair. In both cases, only one of the two alternative, putative evolutionary pathways leads to a functional protein and the corresponding pairs of residue mutations are among those found in present-day cytochromes c. Since valine is predicted to be at position 20 in the ancestral form of cytochrome c, the present data provide an explanation for the ancient requirement of leucine rather than methionine in position 98. The present data provide further evidence for the role of those specific atom–atom interactions in directing a pathway in the evolutionary changes of the amino acid sequence that have taken place in cytochrome c, in accordance with Fitch and Markowitz.
Keywords: %cytochrome c evolution; functional correlation; covarion phenomenon; yeast iso-2-cytochrome c mutation.