Neutrino Mass Matrix Out of Up-Quark Masses Only

Under the assumption of symmetric four zero texture for fermion mass matrices in SO(10) model, the neutrino Dirc mass matrix is derived from the up-quark mass matrix. By adjusting two scales of the Majorana mass sector, we can derive observed neutrino two large mixing angles very naturally. It is indeed remarkable that all the masses and mixings of neutrinos are expressed in terms of only three known parameters, $m_t,m_c,m_u$. A typical example of our model is \tan^2 2\theta_{\tau \mu}=\frac{4}{(1-2\frac{m_c}{\sqrt{m_u m_t}})^2}.