To date, no studies have examined the tooth formation during developmentalstages of brush-tailed mice (Calomyscidae) and true hamsters(Cricetidae). Herein, we compared the timing of tooth morphogenesis andFGF4 expression pattern during development of the first lower molar inGoodwin’s brush-tailed mouse, Calomyscuselburzensiswith two othermuroid rodents; thehouse mouse, Mus musculus(Muridae), model organismfor tooth morphogenesis, and the golden hamster, Mesocricetusauratuswhich shares great similarities in cusp pattern with brush-tailedmice. All three species were bred in captivity and developing embryoswere isolated at different embryonic days (E). Histological evaluation oflower molars was performed andspatiotemporal pattern of FGF4 expressionwas determined by immunohistochemistry. Results indicated thatmorphogenesis of the tooth cusps starts at the beginning of the cap stageof the first lower molar (E14 in house mouse, about E11.5 in golden hamsterand E22 in Goodwin’s brush-tailed mouse). During the cap to bellstage (E15 in house mouse, E12 in golden hamster and at about E24 inGoodwin’s brush-tailed mouse), a decrease in the expression of FGF4 wasobserved in the mesenchyme, except for the cusp tips. According to ourobservations, the developmental process of the first lower molar formationin Goodwin’s brush-tailed mouse began much later as compared with theother two species. Despite the differences in the temporalpattern ofmolar development between these three members of the same superfamily(Muroidea), the correlation in the expression of FGF4 with specificstages of tooth morphogenesis supported its regulatory function.

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