Figure 2. Example arrays. Photos at the top of the figure are from the Aroclor (PCB mixture) exposure; only the control and 10-ppb dose are shown.

ERDC TN-DOER-R4

September 2004

Figure 2.

Example arrays. Photos at the top of the figure are from the Aroclor (PCB mixture) exposure;

only the control and 10-ppb dose are shown. One sector is enlarged to show details, with

examples of up regulation (increase in gene expression, highlighted in red circle) and down

regulation (decrease in gene expression, highlighted in green circle)

RESULTS AND DISCUSSION: Gene responses are dependent on the exposure time, exposure

dose, and contaminant being investigated. Choice of the 16-hr time point for observations in this

study was operationally based. Logistically, post-exposure washing and counting procedures

make it difficult to time exposures with a precision better than +/- 30 minutes. Additionally,

investigations of the time course of gene expression in HepG2 cells have shown that many genes

are approaching maximal induction by 8 to 18 hr, as monitored by real-time PCR (RT-PCR)

(Frueh et al. 2001).