  Taking the (2,2) strings as a starting point, we discuss the equivalent
integrable field theories and analyze their symmetry structure in 2+2
dimensions from the viewpoint of string/membrane unification. Requiring the
Lorentz invariance and supersymmetry in the (2,2) string target space leads to
an extension of the (2,2) string theory to a theory of 2+2 dimensional
supermembranes (M-branes) propagating in a higher dimensional target space. The
origin of the hidden target space dimensions of the M-brane is related to the
maximally extended supersymmetry implied by the Lorentz covariance and
dimensional reasons. The K"ahler-Chern-Simons-type action describing the
self-dual gravity in 2+2 dimensions is proposed. Its maximal supersymmetric
extension (of the Green-Schwarz-type) naturally leads to the 2+10 (or higher)
dimensions for the M-brane target space. The proposed OSp(32|1) supersymmetric
action gives the pre-geometrical description of M-branes, which may be useful
for a fundamental formulation of F&M theory.
