Merging sex and position

Regulation of sexual dimorphism: mutational and chemogenetic analysis of the doublesex DM domain

Doublesex (dsx) is a transcription factor in Drosophila that regulates somatic sexual differentiation. Male- and female-specific splicing isoforms of DSX share a novel DNA-binding domain, designated the DM motif. Broadly conserved among metazoan sex-determining factors, the DM domain contains a nonclassical zinc module and binds in the DNA minor groove. Here, we characterize the DM motif by site-directed and random mutagenesis using a yeast one-hybrid (Y1H) system and extend this analysis by chemogenetic complementation in vitro. The Y1H system is based on a sex-specific Drosophila enhancer element and validated through studies of intersexual dsx mutations. We demonstrate that the eight motif-specific histidines and cysteines engaged in zinc coordination are each critical and cannot be interchanged; folding also requires conserved aliphatic side chains in the hydrophobic core. Mutations that impair DNA binding tend to occur at conserved positions, whereas neutral substitutions occur at nonconserved sites. Evidence for a specific salt bridge between a conserved lysine and the DNA backbone is obtained through the synthesis of nonstandard protein and DNA analogs. Together, these results provide molecular links between the structure of the DM domain and its function in the regulation of sexual dimorphism.

Aging and vocabulary scores: a meta-analysis

Vocabulary scores were examined in a total of 210 articles, containing 324 independent pairings of younger and older adults, from the 1986-2001 issues of Psychology and Aging. The average effect size, favoring the old, was 0.80 SD. Production tests yielded smaller effects (0.68 SD) than multiple-choice tests (0.93 SD). Both age and education were found to be partially independent determinants of performance in production tests; age effects disappeared in multiple-choice tests as soon as education was taken into account. In addition, the Wechsler Adult Intelligence Scale--Revised Vocabulary subtest (D. Wechsler, 1981) was also found to be sensitive to the Flynn effect (J. R. Flynn, 1987; i.e., increasing test scores with advancing birth year). The results question the approach of using age-group equality in vocabulary scores as a check on sample equivalence.

Sex comes in from the cold: the integration of sex and pattern

There has recently been a revolution in our understanding of how the Drosophila sex-determination hierarchy generates somatic sexual dimorphism. Most significantly, the sex hierarchy has been shown to modulate the activities of well-known signaling molecules (FGF, Wnt and TGF beta proteins) and transcription factors (BAB and DAC) to direct various sex-specific aspects of growth and differentiation. As some of the genes encoding these proteins are also the targets of Hox gene action, these and other findings are revealing the levels at which the sex determination and Hox patterning pathways are integrated to control growth, morphogenesis and differentiation.