This study analyzes the impact of intra-sectoral mobility of academics on research productivity and R&D information exchange dynamics in Japan. The analysis shows intra-sectoral mobility impacting positively both research productivity and information exchange dynamics, but that this effect--except for information exchange with peers based abroad--has a threshold. This result highlights the importance of academic job mobility but also alerts for cases of "overloads of mobility," leading us to argue for some degree of stability in academic careers, supported by policies fostering temporary international mobility spells. We also find that the role of foreign academics in the Japanese higher education is one of national and international gatekeepers being this role shaped by where the doctorate was obtained (Japan vs abroad). Japanese academics that have performed the doctorate abroad are also key international gatekeepers.