Ectopic expression of RET results in microphthalmia and tumors in the retinal pigment epithelium.

The retinal pigment epithelium (RPE) is essential for eye development by interacting with the overlaying neuroepithelium. Regulatory sequences of the gene encoding for tyrosinase-related protein 1 (TRP-1), linked to the lacZ reporter gene, lead to strong and specific beta-galactosidase expression in the RPE. We asked how the oncogene ret would affect this epithelial cell type during mouse development. We used the TRP-1 promoter to express ret in the developing RPE, and obtained transgenic mouse lines, which showed mild to severe microphthalmia. During development, the RPE changed to a stratified epithelium with reduced or absent pigmentation from E10.5 onward. In addition, proliferation of RPE cells and tumor formation were observed from E12.5 onward. These early events prevent closure of choroid fissure and lead to microphthalmia and secondary malformations after birth. We conclude that ret transgene expression in the RPE prevents normal differentiation of this epithelial layer and induces proliferation and tumor formation. The appearance of the microphthalmic phenotype underlines the requirement of a normally developed RPE for eye development.

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.

[Dermoid of the cornea. Report of 2 cases of Ida Mann's 2nd type]. / Dermoïdes de la cornée. A propos de deux observations du 2e degré de Ida Mann.

At the opposite of epibulbar dermoids (which are isolated or combined), dermoids of IDA MANN's second type are uncommon. The two cases reported had a big size and covered almost the cornea, without damage on the descemet's membrane, the endothelium and the other eyeball structures. This lesion is classified by the W.H.O. among choristomas. It's made of skin recovering fat which includes in different figures, hair follicle, eccrine and sweat glands. Total excision is the best treatment, but couls become complicated by cornea perforation. It could be followed in some cases by keratoplasty. Amblyopia could go with this malformation.

Association of epibulbar choristomas with linear cutaneous nevi. Review of the literature.

The authors describe the association of epibulbar choristomas with linear cutaneous nevi of the epidermal and sebaceous variety in 24 cases reported in the literature. The choristomas are of the bilateral, extensive, multiple and complex type. The associated ocular and systemic findings include lid and uveal coloboma, lid choristoma, alopecia, convulsions and growth retardation.

Anatomy and embryology of the eyelids: a review with special reference to the development of divided nevi.

In this review of the basic anatomy and embryology of the human eyelids, the sequence of eyelid differentiation is discussed. The development is important in exploring the formation of divided or "kissing" nevi of the lids. Since the lids are fused from the ninth week until the twentieth week of gestation, one may propose that the precursor elements of the nevus develop during that specific time. Because the epithelium only is fused, melanocytes derived from the neural crest must begin their differentiation in the region of the fused epithelium.

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.

Mesectodermal leiomyoma of the ciliary body: a tumor of presumed neural crest origin.

Two benign tumors of the ciliary body diagnosed as neurogenic tumors by light microscopy were shown by electron microscopy to be composed of smooth muscle cells with unusual morphologic features. The light-microscopic appearance of a background fibrillary matrix imparting a "neural" appearance was the result of the interweaving of myriad cell processes filled with thin cytoplasmic filaments possessing fusiform densities. The perikaryon of the tumor cells was relatively free of filaments and displayed mitochondria and stacks of rough-surfaced endoplasmic reticulum suggestive of Nissl substance. The basis for these remarkable "hybrid" tumor cells--combining myogenic and neurogenic characteristics--is believed to reside in the neural crest origin of the smooth muscle of the ciliary body (mesectoderm). The histogenetic implications of mesectodermal tissue and the tumors that it spawns are discussed.