Figure 4: Comparison of benzo(a)pyrene (B(a)P) metabolism in the chicken embryo-fetus and rodents.

C. Differential Gene Expression in Response to B(a)P

The heatmap (Figure 5) demonstrates expression profiles of the top thirty (30) differentially expressed genes which were sorted by their adjusted p-values to identify co-regulated genes across control and dose groups. Ten (10) genes which were significantly deregulated by B(a)P in the livers of chicken embryo-fetuses (were identified based on the log2fold change (Table 2). Out of these, eight (8) genes were upregulated and two (2) were downregulated in the B(a)P dose group when compared to control group (Figure 6).
The genes that had direct and/or indirect effect on CYP1A1 activity were ENSGALG00000013402; ENSGALG00000001325; ENSGALG00000001320; and ENSGALG00000010256. All these four genes were upregulated. ENSGALG00000016186 which affected cyclic GMP activity was also upregulated. Other three genes which were upregulated were ENSGALG00000004508; ENSGALG00000003948 and ENSGALG00000026384 which had effect in DNA repair activity; heme formation and proprotein conversion, respectively. The two downregulated genes namely, ENSGALG00000001416 and ENSGALG00000010293 plays and important role in alpha-1 adrenergic receptor activity and riboflavin transport activity , respectively.
Functional relationships of significantly deregulated genes and their protein-protein interaction network is shown in Figure 7. The majority of genes participate in shared biological pathways or processes, in particular, xenobiotic metabolic process, aromatase activity, and aryl hydrocarbon receptor complex (Table 3).
Pathway enrichment analysis of human orthologs of identified differentially expressed genes identified several enriched pathways, notably Arylhydrocarbon receptor pathway (p = 0.0023) and B(a)P metabolism (p = 0.015) (Figure 8).
These findings were in concordance with a statistically significant increase in the activity of CYP1A1 enzyme in the chicken embryo-fetal livers following injections of B(a)P at 125 and 250 µg/egg (Supplementary Figure 1).