Expression and localization of USF1 in mouse tooth development

Objectives: To detect the expression of USF1 and its temporo-spatial localization during mouse tooth development. Methods: With total RNA extracted from P5d balb/c mouse first molar tooth germ, the desired DNA products were obtained by RT-PCR and inserted into T vectors and transformed into E.Coli DH5a. The DNA of positive clones was testified by sequencing. Total protein was extracted from P1 and P11d mouse first molar tooth germ, and western blot for USF1 was undertaken. Paraffin sections of first molar tooth germ from E13, 16, 19, P1, 5, 8, 11, 21d and 6-month-old adult mouse were prepared respectively and immunohistochemical staining was carried out. Results: DNA sequencing revealed that one segment was consistent with the sequence of USF1 presented in Genebank, and the other one lacked 31 bp at the amino terminal, which was termed as mini USF1 and accepted by Genebank with the accession number AF479773. Western blot analysis identified one 43-kDa protein from P11d mouse tooth germ, but none from P1d mouse. Immunohistochemically, positive staining for USF1 in mouse tooth germ began from P5d, and extended to P11d, which was mainly confined to the cytoplasm of differentiating ameloblasts and odontoblasts, but no staining in bud, cap and early bell stages of tooth germ. However, after tooth eruption on P21d, USF1 became negative again, although it was still positive in the adjacent muscles, and the same result was observed in adult mouse tooth. Conclusion: We verified the expression of USF1 and identified another isoform, mini USF1 in mouse tooth germ for the first time. Moreover, we found that USF1 was mainly localized in differentiating ameloblasts and odontoblasts, and its expression was quite dynamic during mouse tooth development.