Synapse formation in retinoblastoma tumours.

Developing photoreceptor-like cells in retinoblastoma tumour fleurettes were found to contain apical tight junctions, mitochondrial-filled inner segment regions with cilia, and basally located synaptic ribbons and vesicles. Synaptic contract appeared to be established with adjacent neuronal-like elements. We suggest that photoreceptor differentiation in retinoblastoma tumours follows a sequence similar to normal human photoreceptor embryogenesis.