In vivo evidence of IGF-I–estrogen crosstalk in mediating the cortical bone response to mechanical strain

Although insulin-like growth factor-I （IGF-I） and estrogen signaling pathways have been shown to be involved in mediating the bone anabolic response to mechanical loading, it is not known whether these two signaling pathways crosstalk with each other in producing a skeletal response to mechanical loading. To test this, at 5 weeks of age, partial ovariectomy （pOVX） or a sham operation was performed on heterozygous IGF-I conditional knockout （H IGF-I KO） and control mice generated using a Cre-loxP approach. At 10 weeks of age, a 10 N axial load was applied on the right tibia of these mice for a period of 2 weeks and the left tibia was used as an internal non-non-loaded control. At the cortical site, partial estrogen loss reduced total volumetric bone mineral density （BMD） by 5% in control pOVX mice （P=0.05, one-way ANOVA）, but not in the H IGF-I KO pOVX mice. At the trabecular site, bone volume/total volume （BV/TV） was reduced by 5%-6% in both control pOVX （P〈0.05） and H IGF-I KO pOVX （P=0.05） mice. Two weeks of mechanical loading caused a 7 %-8% and an 11%-13% （P〈0.05 vs. non-loaded bones） increase in cortical BMD and cortical thickness （Ct.Th）, respectively, in the control sham, control pOVX and H IGF-I KO sham groups. By contrast, the magnitude of cortical BMD （4%, P=0.13） and Ct.Th （6%, P〈0.05） responses were reduced by 50% in the H IGF-I KO pOVX mice compared to the other three groups. The interaction between genotype and estrogen deficiency on the mechanical loading-induced cortical bone response was significant （P〈0.05） by two-way ANOVA. Two weeks of axial loading caused similar increases in trabecular BV/TV （13%-17%） and thickness （17%-23%） in all four groups of mice. In conclusion, partial loss of both estrogen and IGF-I significantly reduced cortical but not the trabecular bone response to mechanical loading, providing in vivo evidence of the above crosstalk in mediating the bone response to loading.

Identification of differentially-expressed genes of rice in overlapping responses to bacterial infection by Xanthomonas oryzae pv.oryzae and nitrogen deficiency

Bacterial blight of rice caused by Xanthomonas oryzae pv.oryzae（Xoo） is one of high nitrogen（N） responsive diseases.Rice plants became more disease resistant with decreasing N suggesting that the crosstalk between disease resistance and N utilization pathways might exist.However,the co-regulatory components in such crosstalk have not been elucidated.Here,we comparatively analyzed the gene expression profiling of rice under Xoo inoculation,low N treatment,or a combination of both stresses,and identified the differentially-expressed genes（DEGs） in overlapping responses.These DEGs were involved in different biological processes,including innate immunity and nitrogen metabolism.The randomly-selected DEGs expression was validated by quantitative real-time PCR assays.Temporal expression of six genes from different functional categories suggested that N condition was the dominant factor when both stresses were present.These DEGs identified provide novel insights into the coordinated regulatory mechanism in biotic and abiotic stress responses in rice.