Literature has already shown that gestures play a relevant role in classroom interactions between students and teacher. We integrate the perspective of Theory of Semiotic Mediation with the notion of Semiotic Bundle to illustrate how gestures can be used as "pivot signs" in semiotic chains. This means that gestures can be performed by the teacher to link a situated context (such as an activity with a concrete manipulative) to a mathematical shared culture. By analysing a mathematical discussion in grade 5, we identify two different ways in which gestures are exploited as pivot signs in this process, in association with other semiotic modalities.