Histological and Immunohistochemical Studies to Determine the Mechanism of Cleft Palate Induction after Palatal Fusion in Mice Exposed to TCDD

Upregulated LncRNA-Meg3 modulates the proliferation and survival of MEPM cells via interacting with Smad signaling in TCDD-induced cleft palate

Exposure to the environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in utero can result in high rates of cleft palate (CP) formation, yet the underlying mechanisms remain to be characterized. In vivo, the lncRNA Meg3 was upregulated following TCDD treatment in CP-associated murine embryonic palatal tissue, with concomitant changes in proliferative and apoptotic activity in these murine embryonic palatal mesenchymal (MEPM) cells. Meg3 can modulate the TGF-β/Smad to control the proliferation, survival, and differentiation of cells. Accordingly, TCCD and TGF-β1 were herein used to treat MEPM cells in vitro, revealing that while TCDD exposure altered the proliferative activity and apoptotic death of these cells, exogenous TGF-β1 exposure antagonized these effects via TGF-β/Smad signaling. TCDD promoted Meg3 upregulation, whereas TGF-β1 suppressed TCDD-driven upregulation of this lncRNA. Meg3 was additionally determined to directly interact with Smad2, with significant Meg3 enrichment in Smad2-immunoprecipitates following TCDD treatment. When Meg3 was silenced, the impact of TCDD on Smad signaling, proliferative activity, and apoptosis were ablated, while the effects of exogenous TGF-β1 were unchanged. This supports a model wherein Meg3 is upregulated in TCDD-exposed palatal tissue whereupon it can interact with Smad2 to suppress Smad-dependent signaling, thus controlling MEPM cell proliferation and apoptosis, contributing to TCDD-induced CP, which provides a theoretical support for the precautions of cleft palate induced by TCDD.

The mechanisms governing mouse embryonic palate mesenchymal cells' proliferation associated with atRA-induced cleft palate in mice: insights from integrated transcriptomic and metabolomic analyses

While exposure to high levels of all-trans retinoic acid (atRA) during pregnancy is known to suppress murine embryonic palate mesenchymal (MEPM) cells proliferation and to result in cleft palate (CP) development, the underlying mechanisms are poorly understood. Accordingly, this study was designed with the goal of clarifying the etiological basis for atRA-induced CP. A murine model of CP was established via the oral administration of atRA to pregnant mice on gestational day (GD) 10.5, after which transcriptomic and metabolomic analyses were performed with the goal of clarifying the critical genes and metabolites associated with CP development through an integrated multi-omics approach. MEPM cells proliferation was altered by atRA exposure as expected, contributing to CP incidence. In total, 110 genes were differentially expressed in the atRA treatment groups, suggesting that atRA may influence key biological processes including stimulus, adhesion, and signaling-related activities. In addition, 133 differentially abundant metabolites were identified including molecules associated with ABC transporters, protein digestion and absorption, mTOR signaling pathway, and the TCA cycle, suggesting a link between these mechanisms and CP. Overall, combined analyses of these transcriptomic and metabolomic results suggested that the MAPK, calcium, PI3K-Akt, Wnt, and mTOR signaling pathways are particularly important pathways enriched in the palatal cleft under conditions of atRA exposure. Together, these integrated transcriptomic and metabolomic approaches provided new evidence with respect to the mechanisms underlying altered MEPM cells proliferation and signal transduction associated with atRA-induced CP, revealing a possible link between oxidative stress and these pathological changes.

MicroRNAs and Gene Regulatory Networks Related to Cleft Lip and Palate

Cleft lip and palate is one of the most common congenital birth defects and has a complex etiology. Either genetic or environmental factors, or both, are involved at various degrees, and the type and severity of clefts vary. One of the longstanding questions is how environmental factors lead to craniofacial developmental anomalies. Recent studies highlight non-coding RNAs as potential epigenetic regulators in cleft lip and palate. In this review, we will discuss microRNAs, a type of small non-coding RNAs that can simultaneously regulate expression of many downstream target genes, as a causative mechanism of cleft lip and palate in humans and mice.

Transcriptome heterogeneity of congenital cleft palate model in congener New Zealand rabbits induced by dexamethasone

OBJECTIVES

This work aimed to investigate the transcriptome heterogeneity of dexamethasone-induced congenital cleft palate in homozygous New Zealand rabbits and determine the molecular mechanism underlying the occurrence of congenital cleft palate.

METHODS

Dexamethasone (1.0 mg per day) was administered intramuscularly to 20 New Zealand pregnant rabbits from day 14 to day 17 of gestation, and the palatal phenotype of all offspring of each pregnant rabbit was observed. Eight embryos with a 4∶4 ratio of cleft palate to non-cleft palate were selected and divided into the cleft palate group (CP) and non-cleft palate group (NCP). Their palatal tissues were collected for RNA sequencing.

RESULTS

A total of 225 differentially expressed genes (Q<0.05) were found in the CP group compared with the NCP group, of which 120 genes were upregulated and 105 genes were downregulated. The GO and KEGG enrichment analyses of these differentially expressed genes were carried out. The results showed significant enrichment in GO classification, which included heterotrimeric G protein complex, extracellular matrix, transcription factor complex, and basement membrane. Meanwhile, GABA ergic synapse, morphine addiction, retrograde endocannabinoid signaling, glutamate synapse, serotonergic synapse, regulation of actin cytoskeleton, and the Apelin signaling pathway were significantly enriched in the KEGG pathway. Compared with the NCP group, the gene expression levels of ARHGEF6 (P<0.05) and ABI2 (P<0.001) decreased in the CP group, and APC increased (P<0.001); these results were confirmed by real-time polymerase chain reaction.

CONCLUSIONS

Abnormal expression levels of the ARHGEF6, APC, and ABI2 genes involved in the regulation of the actin cytoskeleton in the palatal synapse may be associated with the dexamethasone-induced congenital cleft palate in New Zealand rabbits.