Generation of two H1 hESC sublines carrying a heterozygous and homozygous knock-out of RB1.

Retinoblastoma is a childhood cancer of the retina caused by biallelic inactivation of the tumor suppressor gene RB1. In heritable retinoblastoma, one allele is inherited in mutant form via one of the parental germ cells. To study molecular mechanisms in retinoblastoma, two sublines of H1 hESCs were generated, carrying a knock-out allele of RB1 in the heterozygous or homozygous state. Exon 3 of RB1 was targeted and modified by nucleotide deletions using the CRISPR/Cas9 nuclease system. Based on a nearby single nucleotide polymorphism, the modification could be assigned to one allele.

Optical coherence tomography for live phenotypic analysis of embryonic ocular structures in mouse models.

Mouse models of ocular diseases provide a powerful resource for exploration of molecular regulation of eye development and pre-clinical studies. Availability of a live high-resolution imaging method for mouse embryonic eyes would significantly enhance longitudinal analyses and high-throughput morphological screening. We demonstrate that optical coherence tomography (OCT) can be used for live embryonic ocular imaging throughout gestation. At all studied stages, the whole eye is within the imaging distance of the system and there is a good optical contrast between the structures. We also performed OCT eye imaging in the embryonic retinoblastoma mouse model Pax6-SV40 T-antigen, which spontaneously forms lens and retinal lesions, and demonstrate that OCT allows us to clearly differentiate between the mutant and wild type phenotypes. These results demonstrate that OCTin utero imaging is a potentially useful tool to study embryonic ocular diseases in mouse models.

Embryonic retinal tumors in SV40 T-Ag transgenic mice contain CD133+ tumor-initiating cells.

PURPOSE: Human retinoblastomas form during the proliferative phase of retina development and are caused by mutations that result in absent or functionally defective Rb protein. Similar tumors occur in mice only when multiple Rb gene family members are absent. We asked if retinal tumors can arise from an undifferentiated retinal cell. The tumor-initiating cells isolated from these tumors that formed in early embryonic murine retinas were characterized. METHODS: Transgenic mice were created using a Pax6 promoter to target expression of SV40 large T-antigen (T-Ag) in the undifferentiated murine embryonic retina. T-Ag, which sequesters all Rb family proteins and p53, is expressed in the retina and lens by murine embryonic day 10 (E10) and tumors are observed by E12.5. A cell line that is adherent in serum-containing media and forms neurospheres in supplemented serum-free media was developed from retinal tumors isolated on postnatal day 7. RESULTS: In all, 1.5% of attached cells form neurospheres when transferred to serum-free medium. All cultured cells express T-Ag, confirming that they derive from the original tumors; 0.5% of adherent cells express detectable levels of CD133. CD133+ FACS-sorted cells cultured in serum-free medium form 3-fold more neurospheres than do CD133- cells. Six of seven mice injected with CD133+ cells and one of seven mice injected with CD133- cells formed tumors during a 6-month period. Unlike primary adherent cells, primary and secondary tumors heterogeneously express markers of stem cells and differentiation similar to human retinoblastoma. CONCLUSIONS: CD133+ tumor-initiating cells can originate from proliferating undifferentiated precursor cells.

Immunohistological characterisation of retinoblastoma and related ocular tissue.

The immunohistological reactivity of six retinoblastomas was investigated by means of 18 monoclonal antibodies and compared with that of adult and fetal retina. The antigenic profiles were found to be characteristic for each cell type studied and indicated that a panel of monoclonal antibodies could achieve a specific immunolocalisation not afforded by any single antibody. Immunohistological comparison between retinoblastoma and adult and fetal retinal cells provided evidence of the histogenesis of the tumour. The data suggest that the tumour arises from an early multipotential cell, which retains the capacity to develop differentiation characteristics associated with inner or outer retinal cell types, resulting in a heterogeneous tumour cell population. A cell with such differentiation potential predominates in the retina prior to the primitive neuroepithelial layer division at eight weeks' gestation.

Retinoblastoma and intracranial malignancy.

The occurrence of independent brain tumors in two patients with retinoblastoma is described. One patient with well-differentiated biliteral retinoblastomas developed, over two years later, a pineal tumor but no other metastatic lesions. The pineal tumor was composed of small neuroblastic cells and a second population of larger cells with vesicular nuclei and more abundant cytoplasm. This feature is not characteristic of either primary or metastatic retinoblastoma. In the second patient the symptoms of a brain tumor led to the discovery of a small uniocular, well-differentiated retinoblastoma. The brain tumor was retrochiasmal, highly differentiated (showing areas of photoreceptor differentiation), and interpreted as an ectopic nonmetastatic retinoblastoma. The possible histogenetic origins of the brain tumors are discussed. Patients who develop symptoms of a brain tumor after a prolonged interval since the treatment of their ocular tumors should be suspected of harboring a second intracranial primary.