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First published online January 10, 2007
doi: 10.1242/10.1242/dev.02755

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Hexamerin-based regulation of juvenile hormone-dependent gene expression underlies phenotypic plasticity in a social insect

Entomology and Nematology Department, University of Florida, Gainesville, FL 32611-0620, USA.

View larger version (15K): [in this window] [in a new window]   Fig. 1. Impacts of hexamerin silencing on downstream gene expression. Downstream effects of hexamerin silencing (A) on the expression of 17 putative downstream genes, and the three reference/control genes ß-actin, NADH-dh and HSP-70 (B). Results were determined from quantitative real-time PCR data. See Table 1 for gene abbreviations. The y-axis represents the percentage of gene expression relative to water-injected controls 24 hours after treatment (bars represent the mean of five individuals, each determined in triplicate). Bars with asterisks represent significant differences from water-injected controls at P<0.01 (***), P<0.05 (**) or P<0.1 (*), obtained by pairwise Kruskal-Wallis tests. Error bars represent standard error of the mean (s.e.m.).

View larger version (100K): [in this window] [in a new window]   Fig. 2. Temporal expression changes for 22 genes in R. flavipes workers across days 5, 10 and 15 of isolation experiments. (A,B) Isolation away from the colony (A) and in the presence of 150 µg externally-applied JH III (B). Results are normalized to colony workers at day 0 (shown by arrows at top of A and B). (C) JH III-treatment effects normalized to colony-release effects within each day (shown by arrows in the right portion of C). Yellow and blue cells, respectively, indicate significant increases and decreases in gene expression (P<0.05), whereas black cells indicate no change (P>0.05). Statistical analyses were made using the Kruskal-Wallis test from three independent replications, each determined in triplicate. See Table 1 for gene abbreviations. Values presented in individual cells are means, with standard error (s.e.m.) shown in parentheses.

View larger version (30K): [in this window] [in a new window]   Fig. 3. Comparison of gene expression by linear regression analysis. Linear regressions comparing the expression of 17 genes between hexamerin silencing experiments and experiments involving (top row) isolation away from the colony, and (bottom row) isolation on JH III deposits at days 5 (left), 10 (middle) and 15 (right) of isolation. Correlation coefficients and P-values were determined using PROC REG in the SAS software package. Colony-release results shown across the top row indicate no significant correlation with hexamerin silencing, whereas JH-dependent results in the bottom row show significant correlations with hexamerin silencing for all days (P<0.05). Also, all JH regressions in the bottom row improve after the removal of the apparent outlier genes apoptosis inhibitor, ATPase, larval cuticle protein, nanos and SH3 kinase (compare full and reduced models). See Fig. 1 and Fig. 2A,C for original data presentations and standard error (s.e.m.) estimates that correspond to each data point.

View larger version (17K): [in this window] [in a new window]   Fig. 4. Diagrams depicting developmental gene networks and proposed gene relationships, as suggested by the current research. (A) Organization of a gene network involving JH-responsive genes from the signal transduction, transcription and translation factors, and the cuticle and muscle ontogeny categories. Solid arrows represent a simple hierarchical cascade, whereas dotted arrows represent the more complex feedback between levels that probably occurs. (B) Apparent relationship between hexamerin titer and JH availability (Zhou et al., 2006a; Zhou et al., 2006b), as well as other putative intrinsic and extrinsic caste-regulatory factors. Solid arrows represent what is known from prior and current research, whereas dotted arrows illustrate the proposed relationships. In this scheme, the hexamerins can be considered an environmentally-responsive switching mechanism (Wheeler, 1986) that modulates JH-dependent morphogenesis.

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