An Allometric Analysis of Sex and Sex Chromosome Dosage Effects on Subcortical Anatomy in Humans.

Structural neuroimaging of humans with typical and atypical sex-chromosome complements has established the marked influence of both Yand X-/Y-chromosome dosage on total brain volume (TBV) and identified potential cortical substrates for the psychiatric phenotypes associated with sex-chromosome aneuploidy (SCA). Here, in a cohort of 354 humans with varying karyotypes (XX, XY, XXX, XXY, XYY, XXYY, XXXXY), we investigate sex and SCA effects on subcortical size and shape; focusing on the striatum, pallidum and thalamus. We find large effect-size differences in the volume and shape of all three structures as a function of sex and SCA. We correct for TBV effects with a novel allometric method harnessing normative scaling rules for subcortical size and shape in humans, which we derive here for the first time. We show that all three subcortical volumes scale sublinearly with TBV among healthy humans, mirroring known relationships between subcortical volume and TBV among species. Traditional TBV correction methods assume linear scaling and can therefore invert or exaggerate sex and SCA effects on subcortical anatomy. Allometric analysis restricts sex-differences to: (1) greater pallidal volume (PV) in males, and (2) relative caudate head expansion and ventral striatum contraction in females. Allometric analysis of SCA reveals that supernumerary X- and Y-chromosomes both cause disproportionate reductions in PV, and coordinated deformations of striatopallidal shape. Our study provides a novel understanding of sex and sex-chromosome dosage effects on subcortical organization, using an allometric approach that can be generalized to other basic and clinical structural neuroimaging settings.

Identification of drug modulators targeting gene-dosage disease CMT1A.

The structural integrity of myelin formed by Schwann cells in the peripheral nervous system (PNS) is required for proper nerve conduction and is dependent on adequate expression of myelin genes including peripheral myelin protein 22 (PMP22). Consequently, excess PMP22 resulting from its genetic duplication and overexpression has been directly associated with the peripheral neuropathy called Charcot-Marie-Tooth disease type 1A (CMT1A), the most prevalent type of CMT. Here, in an attempt to identify transcriptional inhibitors with therapeutic value toward CMT1A, we developed a cross-validating pair of orthogonal reporter assays, firefly luciferase (FLuc) and ß-lactamase (ßLac), capable of recapitulating PMP22 expression, utilizing the intronic regulatory element of the human PMP22 gene. Each compound from a collection of approximately 3,000 approved drugs was tested at multiple titration points to achieve a pharmacological end point in a 1536-well plate quantitative high-throughput screen (qHTS) format. In conjunction with an independent counter-screen for cytotoxicity, the design of our orthogonal screen platform effectively contributed to selection and prioritization of active compounds, among which three drugs (fenretinide, olvanil, and bortezomib) exhibited marked reduction of endogenous Pmp22 mRNA and protein. Overall, the findings of this study provide a strategic approach to assay development for gene-dosage diseases such as CMT1A.

Tomato phenylalanine ammonia-lyase gene family, highly redundant but strongly underutilized.

Phenylalanine ammonia-lyase (PAL) is an important enzyme in both plant development and pathogen defense. In all plants it is encoded by a multi-gene family, ranging in copy number from four in Arabidopsis to a dozen or more copies in some higher plants. Many studies indicate that alternate genes are differentially regulated in response to environmental stimuli. In this study, Southern blot and dot blot analyses in tomato indicate a surprisingly large family of related sequences with approximately 26 copies in the diploid genome, some easily distinguished by restriction enzyme digestion. Analyses of a BAC genome library suggest that the genes are generally not clustered. A more detailed comparison of the gene sequences using PCR to isolate the individual copies and reverse transcription-PCR to study the transcripts that they encode indicates a significant diversity in the gene sequences themselves, but surprisingly only one mRNA transcript can be detected even when additional expression is induced by pathogen growth or wounding. Consistent with previous reports in other plants, a parallel study with a closely related plant, the potato, indicates a much broader utilization of the PAL genes, highlighting the unusual nature of this family in tomato and of the mechanism(s) that silences so many members. Plant transformation analyses further demonstrate the presence of very active silencing, suggesting aggressive competition between PAL gene duplication and copy inactivation during PAL gene evolution.

Auxin response factors ARF6 and ARF8 promote jasmonic acid production and flower maturation.

Pollination in flowering plants requires that anthers release pollen when the gynoecium is competent to support fertilization. We show that in Arabidopsis thaliana, two paralogous auxin response transcription factors, ARF6 and ARF8, regulate both stamen and gynoecium maturation. arf6 arf8 double-null mutant flowers arrested as infertile closed buds with short petals, short stamen filaments, undehisced anthers that did not release pollen and immature gynoecia. Numerous developmentally regulated genes failed to be induced. ARF6 and ARF8 thus coordinate the transition from immature to mature fertile flowers. Jasmonic acid (JA) measurements and JA feeding experiments showed that decreased jasmonate production caused the block in pollen release, but not the gynoecium arrest. The double mutant had altered auxin responsive gene expression. However, whole flower auxin levels did not change during flower maturation, suggesting that auxin might regulate flower maturation only under specific environmental conditions, or in localized organs or tissues of flowers. arf6 and arf8 single mutants and sesquimutants (homozygous for one mutation and heterozygous for the other) had delayed stamen development and decreased fecundity, indicating that ARF6 and ARF8 gene dosage affects timing of flower maturation quantitatively.