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).