characterization-vitro-differentiation-human-primary-keratinocytes

Characterization of In Vitro Differentiation of Human Primary Keratinocytes by RNA-Seq Analysis

Human primary keratinocytes are often used as in vitro models for studies on epidermal differentiation and related diseases. Methods have been reported ...

Radboud University, Nijmegen, The Netherlands

Radboud University Medical Center, Nijmegen, The Netherlands

The transcription factor p63 plays a pivotal role in keratinocyte proliferation and differentiation in the epidermis. However, how p63 regulates epidermal genes during differentiation is not yet clear. Using epigenome profiling of differentiating human primary epidermal keratinocytes, we characterized a catalog of dynamically regulated genes and p63-bound regulatory elements that are relevant for epithelial development and related diseases. p63-bound regulatory elements occur as single or clustered enhancers, and remarkably, only a subset is active as defined by the co-presence of the active enhancer mark histone modification H3K27ac in epidermal keratinocytes. We show that the dynamics of gene expression correlates with the activity of p63-bound enhancers rather than with p63 binding itself. The activity of p63-bound enhancers is likely determined by other transcription factors that cooperate with p63. Our data show that inactive p63-bound enhancers in epidermal keratinocytes may be active during the development of other epithelial-related structures such as limbs and suggest that p63 bookmarks genomic loci during the commitment of the epithelial lineage and regulates genes through temporal- and spatial-specific active enhancers.

Transcription factor p63 bookmarks and regulates dynamic enhancers during epidermal differentiation.

Orofacial clefts (OFCs) represent a large fraction of human birth defects and are one of the most common phenotypes affected by large copy number variants (CNVs). Due to the limited number of CNV patients in individual centers, CNV analyses of a large number of OFC patients are challenging. The present study analyzed 249 genomic deletions and 226 duplications from a cohort of 312 OFC patients reported in two publicly accessible databases of chromosome imbalance and phenotype in humans, DECIPHER and ECARUCA. Genomic regions deleted or duplicated in multiple patients were identified, and genes in these overlapping CNVs were prioritized based on the number of genes encompassed by the region and gene expression in embryonic mouse palate. Our analyses of these overlapping CNVs identified two genes known to be causative for human OFCs, SATB2 and MEIS2, and 12 genes (DGCR6, FGF2, FRZB, LETM1, MAPK3, SPRY1, THBS1, TSHZ1, TTC28, TULP4, WHSC1, WHSC2) that are associated with OFC or orofacial development. Additionally, we report 34 deleted and 24 duplicated genes that have not previously been associated with OFCs but are associated with the BMP, MAPK and RAC1 pathways. Statistical analyses show that the high number of overlapping CNVs is not due to random occurrence. The identified genes are not located in highly variable genomic regions in healthy populations and are significantly enriched for genes that are involved in orofacial development. In summary, we report a CNV analysis pipeline of a large cohort of OFC patients and identify novel candidate OFC genes. 

Systematic analysis of copy number variants of a large cohort of orofacial cleft patients identifies candidate genes for orofacial clefts.

The CCTC-binding factor (CTCF) protein is involved in genome organization, including mediating three-dimensional chromatin interactions. Human patient lymphocytes with mutations in a single copy of the CTCF gene have reduced expression of enhancer-associated genes involved in response to stimuli. We hypothesize that CTCF interactions stabilize enhancer-promoter chromatin interaction domains, facilitating increased expression of genes in response to stimuli. Here we systematically investigate this model using computational analyses.

CTCF-mediated chromatin loops enclose inducible gene regulatory domains.

The transcription factor p63 regulates epidermal genes and the enhancer landscape in skin keratinocytes. Its molecular function in controlling the chromatin structure is, however, not yet completely understood. Here, we integrated multi-omics profiles, including the transcriptome, transcription factor DNA-binding and chromatin accessibility, in skin keratinocytes isolated from EEC syndrome patients carrying p63 mutations, to examine the role of p63 in shaping the chromatin architecture. We found decreased chromatin accessibility in p63- and CTCF-bound open chromatin regions that potentially contributed to gene deregulation in mutant keratinocytes. Cooperation of p63 and CTCF seemed to assist chromatin interactions between p63-bound enhancers and gene promoters in skin keratinocytes. Our study suggests an intriguing model where cell type-specific transcription factors such as p63 cooperate with the genome organizer CTCF in the three-dimensional chromatin space to regulate the transcription program important for the proper cell identity.

p63 cooperates with CTCF to modulate chromatin architecture in skin keratinocytes.

Mutations in transcription factor p63 are associated with developmental disorders that manifest defects in stratified epithelia including the epidermis. The underlying cellular and molecular mechanism is however not yet understood. We established an epidermal commitment model using human induced pluripotent stem cells (iPSCs) and characterized differentiation defects of iPSCs derived from ectrodactyly, ectodermal dysplasia, and cleft lip/palate (EEC) syndrome patients carrying p63 mutations. Transcriptome analyses revealed stepwise cell fate transitions during epidermal commitment: Specification from multipotent simple epithelium to basal stratified epithelia and ultimately to the mature epidermal fate. Differentiation defects of EEC iPSCs caused by p63 mutations occurred during the specification switch from the simple epithelium to the basal-stratified epithelial fate. Single-cell transcriptome and pseudotime analyses of cell states identified mesodermal activation that was associated with the deviated commitment route of EEC iPSCs. Integrated analyses of differentially regulated genes and p63-dependent dynamic genomic enhancers during epidermal commitment suggest that p63 directly controls epidermal gene activation at the specification switch and has an indirect effect on mesodermal gene repression. Importantly, inhibitors of mesodermal induction enhanced epidermal commitment of EEC iPSCs. Our findings demonstrate that p63 is required for specification of stratified epithelia, and that epidermal commitment defects caused by p63 mutations can be reversed by repressing mesodermal induction. This study provides insights into disease mechanisms underlying stratified epithelial defects caused by p63 mutations and suggests potential therapeutic strategies for the disease.

Article	Year
Transcription factor p63 bookmarks and regulates dynamic enhancers during epidermal differentiation. EMBO reports\| PubMed ID: 26034101	2015
Systematic analysis of copy number variants of a large cohort of orofacial cleft patients identifies candidate genes for orofacial clefts. Human genetics\| PubMed ID: 26561393	2016
CTCF-mediated chromatin loops enclose inducible gene regulatory domains. BMC genomics\| PubMed ID: 27004515	2016
p63 cooperates with CTCF to modulate chromatin architecture in skin keratinocytes. Epigenetics & chromatin\| PubMed ID: 31164150	2019
Single-cell RNA-seq identifies a reversible mesodermal activation in abnormally specified epithelia of p63 EEC syndrome. Proceedings of the National Academy of Sciences of the United States of America\| PubMed ID: 31413199	2019

Huiqing Zhou

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