Molecular aspects of cell proliferation and neurogenesis in planarians

An MCM2 gene (DjMCM2) which represents a suitable molecular marker for dete cting proliferating neoblasts was isolated in planarians. Neoblasts are the only self-renewing cells in these organisms and may be able to differentia te into all cell types lost to physiological turnover or injury. To underst and the molecular basis leading to neoblast commitment to a differentiative fate, some regulatory genes were cloned. Our interest was focused on the p rocess of nerve cell differentiation. DjXnp, a planarian gene coding for a protein similar to Xnp/ATRX, a DNA helicase involved in mammalian brain dev elopment via chromatin structure modification, was obtained by RT-PCR. A si milar strategy was also used to clone two different Pax-6-related planarian genes. Identification of factors involved at different levels in the contr ol of gene expression during nerve cell differentiation could be of importa nce to understand the regulatory programs, which operate during neoblast di fferentiation in planarians.