The best miRNA biomarkers are likely to be those that indicate injury or perturbation to a specific cell type, such as the previously discussed hepatocyte-specific miR-122. Other cell-specific miRNAs that may be useful biomarkers of tissue injury include the myomiRs, miRs-133, -206, -208, and -499, which have shown promise through their ability to identify cardiac injury (Jenike and Halushka 2021). In addition, miRNA biomarkers that indicate the disruption of specific nuclear receptor or regulatory pathways as a result of chemical exposure would be desirable. Studies examining the changes in miRNA–mRNA interactions that are due to environmental exposures will be helpful in determining the mechanistic pathways involved. One such study applied a network approach, integrative Joint Random Forest, to investigate the effect of low-dose environmental chemical exposure on normal mammary gland development in rats (Petralia et al. 2017). The researchers detected miRNAs that regulated