We study the inclusion of point and string matter in the deSitter gauge
theory, or MacDowell-Mansouri formulation of four dimensional gravity. We
proceed by locally breaking the gauge symmetries of general relativity along
worldlines and worldsheets embedded in the spacetime manifold. Restoring full
gauge invariance introduces new dynamical fields which describe the dynamics of
spinning matter coupled to gravity. We discuss the physical interpretation of
the obtained formalism by studying the flat limit and the spinless case on
arbitrary backgrounds. It turns out that the worldline action describes a
massive spinning particle, while the worldsheet action contains the Nambu-Goto
string augmented with spinning contributions. Finally, we study the
gravity/matter variational problem and conclude by discussing potential
applications of the formalism to the inclusion of the Nambu-Goto string in
spinfoam models of four dimensional quantum gravity.Comment: 30 pages, no figure