  We investigate electron interferometry of edge states in Topological
Insulators. We show that, when inter-boundary coupling is induced at two
quantum point contacts of a four terminal setup, both Fabry-P\'erot-like and
Aharonov-Bohm-like loop processes arise. These underlying interference effects
lead to a full electrically controllable system, where the magnitude of charge
and spin linear conductances can be tuned by gate voltages, without applying
magnetic fields. In particular we find that, under appropriate conditions,
inter-boundary coupling can lead to negative values of the conductance.
Furthermore, the setup also allows to selectively generate pure charge or pure
spin currents, by choosing the voltage bias configuration.
