Cis‐control of Six1 expression in neural crest cells during craniofacial development

Abstract

Background Six1 is a transcriptional factor that plays an important role in embryonic development. Mouse and chick embryos deficient for Six1 have multiple craniofacial anomalies in the facial bones and cartilages. Multiple Six1 enhancers have been identified, but none of them has been reported to be active in the maxillary and mandibular process. Results We studied two Six1 enhancers in the chick neural crest tissues during craniofacial development. We showed that two evolutionarily conserved enhancers, Six1E1 and Six1E2, act synergistically. Neither Six1E1 nor Six1E2 alone can drive enhancer reporter signal in the maxillary or mandibular processes. However, their combination, Six1E, showed robust enhancer activity in these tissues. Similar reporter signal can also be driven by the mouse homolog of Six1E. Mutations of multiple conserved transcriptional factor binding sites altered the enhancer activity of Six1E, especially mutation of the LIM homeobox binding site, dramatically reduced the enhancer activity, implying that the Lhx protein family be an important regulator of Six1 expression. Conclusion This study, for the first time, described the synergistic activation of two Six1 enhancers in the maxillary and mandibular processes and will facilitate more detailed studies of the regulation of Six1 in craniofacial development.

Six1 is required for signaling center formation and labial‐lingual asymmetry in developing lower incisors

“…Six family transcription factors are composed of Six family members (SIX1‐SIX6) (see also reviews in References 13,14) and play crucial roles in sensory organ and craniofacial development 15‐22 . The mandibular bones of Six1 −/− mice are shorter than those of wild‐type fetuses, but the upper incisors are normally formed in the maxillary process 17 .…”

Rapid induction and long-term self-renewal of neural crest-derived ectodermal chondrogenic cells from hPSCs

“…Well-acknowledged markers of the development of the CNC, such as DLX2, AP-2 and ETS1 24 , were highly expressed during the induction process. NESTIN, an NC stem cell marker 57 , and SIX 1, a crucial transcription factor in facial bone and cartilage development 58 , were uniformly expressed in ECCs, as observed by immunofluorescent staining. Above all, the present method enables the long-term expansion of ECCs without loss of the ability to self-renew.…”

Limb Mesoderm and Head Ectomesenchyme Both Express a Core Transcriptional Program During Chondrocyte Differentiation

“…Upregulated genes in limb IMM and MAT included several HOX genes, DLX5, TBX5, and SHOX2, all of which are known to have a role during limb morphogenesis (Figures 5A,B, labelled green in GRN; Agarwal et al, 2003;Koziel et al, 2005;Yu et al, 2007;Kruger and Kappen 2010;Vieux-Rochas et al, 2013;Tan et al, 2018;Yamamoto et al, 2019). The other portion of the IMM GRN included genes upregulated in the head that are involved in neural crest related processes, such as ZIC1, SIX1, SIX4, PAX7, ID1, GATA2, GATA3, and MSX2, as identified by gene ontology analyses and previous studies (Figure 5A, labelled orange in the GRN; Han et al, 2007;Murdoch et al, 2012;Simões-Costa and Bronner 2013;Garcez et al, 2014;Plouhinec et al, 2014;Simões-Costa and Bronner 2015;Wu et al, 2019;Seal and Monsoro-Burq 2020). Similar to the IMM GRN, SIX1, and SIX4 were also upregulated in the head in one portion of the MAT GRN.…”

“…Many neural crest-dependent biological processes were enriched specifically in ceratobranchial IMM and MAT transcriptomes, such as cranial skeleton morphogenesis, cell migration, neuron differentiation, middle ear morphogenesis, heart development, and melanocyte differentiation (Figure 2B). Many orthologs of a proposed GRN driving neural crest-derived cartilage, such as PAX7, SIX1, and ID1, were also identified (Figure 2B; Meulemans and Bronner-Fraser 2005;Meulemans and Bronner-Fraser 2007;Betancur et al, 2010;Murdoch et al, 2012;Wu et al, 2019).…”