Heterozygous deletion of Six2, which encodes a member of sine oculis homeobox family transcription factors, has recently been associated with the frontonasal dysplasia syndrome FND4. Previous studies showed that Six2 is expressed in multiple tissues during craniofacial development in mice, including embryonic head mesoderm, postmigratory frontonasal neural crest cells, and epithelial and mesenchymal cells of the developing palate and nasal structures. Whereas Six2 ^−/− mice exhibited cranial base defects but did not recapitulate frontonasal phenotypes of FND4 patients, Six1 ^−/‐Six2 ^−/− double mutant mice showed severe craniofacial defects including midline facial clefting. The complex phenotypes of FND4 patients and of Six1 ^−/‐Six2 ^−/− mutant mice indicate that Six2 plays crucial roles in distinct cell types at multiple stages of craniofacial morphogenesis. Here we report generation of mice carrying insertions of a pair of loxP sites flanking exon‐1 of the Six2 gene (Six2 ^f allele) using CRISPR/Cas9‐mediated genome editing. We show that the Six2 ^f allele functions normally and is effectively inactivated by Cre‐mediated recombination in vivo. Furthermore, we show that Six2 ^f/f;Wnt1‐Cre mice recapitulated cranial base defects but not neonatal lethality of Six2 ^−/− mice. These results indicate that Six2 ^f/f mice enable systematic investigation of cell type‐ and stage‐specific Six2 function in development and disease.

中文翻译：

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Six2 条件小鼠的产生和表征。

Six2（编码正弦眼同源盒家族转录因子的成员）的杂合缺失最近与额鼻发育不良综合征 FND4 相关。先前的研究表明，Six2在小鼠颅面发育过程中的多个组织中表达，包括胚胎头部中胚层、迁移后额鼻神经嵴细胞以及发育中的上颚和鼻结构的上皮和间质细胞。Six2 − ^/−小鼠表现出颅底缺陷，但没有重现 FND4 患者的额鼻表型，而Six1 ^−/− Six2 ^−/−双突变小鼠表现出严重的颅面缺陷，包括中线面部裂痕。FND4 患者和Six1 ^−/‐ Six2 ^−/−突变小鼠的复杂表型表明 Six2 在颅面形态发生的多个阶段的不同细胞类型中发挥着至关重要的作用。在此，我们报告了使用 CRISPR/Cas9 介导的基因组编辑技术产生的小鼠，其在Six2基因（Six2 ^f等位基因）的外显子 1 侧翼插入了一对 loxP 位点。我们发现Six2 ^f等位基因功能正常，并且在体内通过 Cre 介导的重组有效失活。此外，我们发现Six2 ^f/f ;Wnt1-Cre小鼠重现了颅底缺陷，但没有重现Six2 ^-/−小鼠的新生儿致死率。这些结果表明Six2 ^f/f小鼠能够系统地研究细胞类型和阶段特异性 Six2 在发育和疾病中的功能。