title: Prenatal exposure to TCDD triggers significant modulation of microRNA expression profile in the thymus that affects consequent gene expression.
abstract: BACKGROUND
  MicroRNAs (miRs) are a class of small RNAs that regulate gene expression. There are over 700 miRs encoded in the mouse genome and modulate most of the cellular pathways and functions by controlling gene expression. However, there is not much known about the pathophysiological role of miRs. TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), an environmental contaminant is well known to induce severe toxicity (acute and chronic) with long-term effects. Also, in utero exposure of fetus to TCDD has been shown to cause thymic atrophy and alterations in T cell differentiation. It is also relevant to understand "the fetal basis of adult disease" hypothesis, which proposes that prenatal exposure to certain forms of nutritional and environmental stress can cause increased susceptibility to clinical disorders later in life. In the current study, therefore, we investigated the effects of prenatal exposure to TCDD on miR profile in fetal thymocytes and searched for their possible role in causing thymic atrophy and alterations in the expression of apoptotic genes.
  
  
  RESULTS
  miR arrays of fetal thymocytes post exposure to TCDD and vehicle were performed. Of the 608 mouse miRs screened, 78 miRs were altered more than 1.5 fold and 28 miRs were changed more than 2 fold in fetal thymocytes post-TCDD exposure when compared to vehicle controls. We validated the expression of several of the miRs using RT-PCR. Furthermore, several of the miRs that were downregulated contained highly complementary sequence to the 3'-UTR region of AhR, CYP1A1, Fas and FasL. Also, the Ingenuity Pathway Analysis software and database was used to analyze the 78 miRs that exhibited significant expression changes and revealed that as many as 15 pathways may be affected.
  
  
  CONCLUSIONS
  These studies revealed that TCDD-mediated alterations in miR expression may be involved in the regulation of its toxicity including cancer, hepatic injury, apoptosis, and cellular development.
authors.affiliation: Department of Pathology, Microbiology & Immunology, University of South Carolina School of Medicine, Columbia, South Carolina, United States of America.
authors.forename: Narendra P
authors.initials: NP
authors.lastname: Singh
authors.forename: Udai P
authors.initials: UP
authors.lastname: Singh
authors.forename: Hongbing
authors.initials: H
authors.lastname: Guan
authors.forename: Prakash
authors.initials: P
authors.lastname: Nagarkatti
authors.forename: Mitzi
authors.initials: M
authors.lastname: Nagarkatti
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D016000:Cluster Analysis; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism; D053222:Fas Ligand Protein / Q000235:genetics / Q000378:metabolism; D005260:Female; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects*; D053263:Gene Regulatory Networks; D018811:Maternal Exposure; D051379:Mice; D035683:MicroRNAs / Q000235:genetics*; D009369:Neoplasms / Q000235:genetics; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology* / Q000633:toxicity; D011247:Pregnancy; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism; D015203:Reproducibility of Results; D015398:Signal Transduction / Q000187:drug effects; D060168:Thymocytes / Q000187:drug effects / Q000378:metabolism; D013950:Thymus Gland / Q000187:drug effects* / Q000196:embryology / Q000378:metabolism*; D019014:fas Receptor / Q000235:genetics / Q000378:metabolism
chemical_list: D053222:Fas Ligand Protein; D035683:MicroRNAs; D000072317:Polychlorinated Dibenzodioxins; D018336:Receptors, Aryl Hydrocarbon; D019014:fas Receptor; C542687:mirnlet7 microRNA, mouse; D019363:Cytochrome P-450 CYP1A1