  Several independent observations have suggested that catastrophe transition
in microtubules is not a first-order process, as is usually assumed. Recent
{\it in vitro} observations by Gardner et al.[ M. K. Gardner et al., Cell
{\bf147}, 1092 (2011)] showed that microtubule catastrophe takes place via
multiple steps and the frequency increases with the age of the filament. Here,
we investigate, via numerical simulations and mathematical calculations, some
of the consequences of age dependence of catastrophe on the dynamics of
microtubules as a function of the aging rate, for two different models of
aging: exponential growth, but saturating asymptotically and purely linear
growth. The boundary demarcating the steady state and non-steady state regimes
in the dynamics is derived analytically in both cases. Numerical simulations,
supported by analytical calculations in the linear model, show that aging leads
to non-exponential length distributions in steady state. More importantly,
oscillations ensue in microtubule length and velocity. The regularity of
oscillations, as characterized by the negative dip in the autocorrelation
function, is reduced by increasing the frequency of rescue events. Our study
shows that age dependence of catastrophe could function as an intrinsic
mechanism to generate oscillatory dynamics in a microtubule population,
distinct from hitherto identified ones.
