Morphological, immunophenotypical and gene expression changes induced by ATRA. Neuronal differentiation in the I-type cell line SK-N-Be2C: A. 60 days of ATRA treatment. Arrow: neurosphere in formation. B. not-treated negative control culture. C. GD2 expression in newly formed floating neurosphere at day 15 of ATRA treatment. D. Calcyclin expression at day 60 of ATRA treatment. White arrow: calcyclin positive cell that appear during neuronal differentiation induction treatment. Gene expression changes of calcyclin (E) and GD2 synthase (F) in LA1-55N, LA1-5S and SK-N-ER cell lines. q-RT-PCR analysis was performed by triplicate of two separate differentiation experiments (60 days induction and 30 days of treatment depletion (90). RA-IND: ATRA induction period.