Genetic and epigenetic mechanisms in the aetiology of orofacial clefts

Author(s)

Lucas Alvizi Cruz

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2017-09-29

Examining board members

Maria Rita dos Santos e Passos Bueno; Dirce Maria Carraro; Angela Maria Vianna Morgante

• Advisor: Maria Rita dos Santos e Passos Bueno

Abstract

Craniofacial development is a tightly regulated event that requires expression of many genes at a precise space-temporal specificity. Interference in the regulation of such genes and their pathways is known to lead to abnormal phenotypes affecting the face and cranium. In this manner, regulation of these pathways is further complicated by interaction between genetic and environmental factors such that disturbance to either may result in craniofacial malformation, as orofacial clefts. Despite several at-risk loci have been identified, they do not completely explain the high heritability observed for the orofacial clefts and many questions remain open. For example, concerning the orofacial clefts transcriptome, the gene pathways which may be dysregulated and the affected cellular processes are still poorly understood. Further, if there is gene expression dysregulation in orofacial clefts, the causes leading to that need to be elucidated, such as the investigation of epigenetic factors. Also, since the multifactorial contribution makes environment relevant to this malformation, epigenetic and epigenomic differences in orofacial clefts should clarified. At last, rare syndromic forms of orofacial clefts with still unknown molecular cause and mechanisms should be elucidated in order to better understand craniofacial development and their impact in non-syndromic forms. Therefore, the main objective of this study was to investigate the molecular mechanisms involved in the aetiology of orofacial clefts, which was focused in gene expression and epigenetic analysis in non-syndromic cleft lip and/or palate (NSCL/P) as well as genetic, gene expression, animal modelling and epigenetics in Richieri-Costa-Pereira Syndrome (RCPS), a rare autosomal recessive syndromic form of orofacial cleft. We found significant transcriptome differences in NSCL/P in comparison to controls, revealing the BRCA1-dependent DNA damage repair pathway as compromised in NSCL/P cells leading to DNA damage accumulation. Next, we studied the potential of DNA methylation in those cells and found a slight but significant increase of BRCA1 promoter DNA methylation in NSCL/P cells and a distinct DNA methylation distribution, point to a possible epigenetic contribution in this phenomenon. We also evaluated the contribution of DNA methylation in 8q24.21 region, one of the most replicated regions in NSCL/P Genome-wide association studies and found no significant differences in our sample. Attempting to investigate DNA methylation in NSCL/P in an epigenomic level, we analysed methylomes and found 578 methylation variable positions in NSCL/P, highly enriched in regulatory regions and in relevant gene pathways for craniofacial development as Epithelial-Mesenchymal Transition pathway. We also studied effect of DNA methylation in familial NSCL/P displaying incomplete penentrance and found a significant increase of CDH1 promoter hypermethylation in penetrant cases in comparison to non-penetrants. Finally, by the use of different sequencing strategies and identity-by-descent analysis we mapped the mutation region of RCPS to EIF4A3 5\'UTR/promoter and found a complex structure of expanded repeats in RCPS patients leading to EIF4A3 downregulation. We were also able to validate the phenotypes using an animal modelling strategy in zebrafish. Because those repeats are CG rich, we investigated whether they were submitted to DNA hypermethylation in RCPS patients as a cause for EIF4A3 hypomorphism, however we found no evidence of methylation increase in RCPS. In conclusion, we were able to associate dysregulated pathways to NSCL/P susceptibility and DNA methylation differences to both non-familial and familial NSCLP. Besides, we were able to identify the genetic cause of RCPS, which now can be molecularly diagnosed. Altogether, our results add to the understanding of craniofacial development and the aetiology of orofacial clefts (AU)

• FAPESP's process: 11/23653-4 - Epigenetic and microRNAs analysis in the DNA repair pathway dysregulation in non syndromic cleft lip-palate patients
• Grantee: Lucas Alvizi Cruz
• Support Opportunities: Scholarships in Brazil - Doctorate (Direct)