Six1, known as Sine oculis homeobox homolog 1, is a transcription factor. It has pivotal roles in organismal development and differentiation, regulating the expression of proteins involved in organ development during embryogenesis [2,4]. Six1 participates in multiple cancer-related signaling pathways such as estrogen, WNT, and MAPK, and is associated with tumorigenesis [1].

In a Six1 knockout mouse model (Six1 -/-) and a cranial neural crest-specific, Six1 conditional knockout mouse model (Six1 f/f ; Wnt1-Cre), the knockout of Six1 led to abnormal expression of osteogenic genes within the mandible and multiple craniofacial deformities, demonstrating its critical role in regulating mandibular skeleton formation during mouse embryogenesis [5]. In breast cancer, in vitro and in vivo experiments validated its positive regulation effect on breast cancer stem cells, showing it can promote the increase in the proportion of stem cells and tumor progression [1]. In Ewing Sarcoma, contrary to its metastasis-enhancing role in most tumors, SIX1 suppresses metastasis by co-regulating EWS/FLI1 target genes [3].

In conclusion, Six1 is crucial for normal organ development, especially mandibular skeleton formation as revealed by KO/CKO mouse models. In disease, it plays diverse roles, promoting tumorigenesis in breast cancer while having an unexpected anti-metastatic function in Ewing Sarcoma. Understanding Six1's functions through these models provides insights into development and disease mechanisms, potentially guiding diagnostic, prognostic, and therapeutic strategies [1,2,3,5].