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. 1998 Aug;82(8):953–960. doi: 10.1136/bjo.82.8.953

Pigmented uveal tumours in a transgenic mouse model

T Kramer 1, M Powell 1, M Wilson 1, J Salvatore 1, H Grossniklaus 1
PMCID: PMC1722710  PMID: 9828784

Abstract

AIMS/BACKGROUND—The authors have developed transgenic mouse strains at the Arizona Cancer Center using a tyrosinase promoter to target expression of the mutated T24 Ha-ras gene in melanin producing cells. Histopathology and electron microscopy (EM) were performed to characterise the intraocular tumours observed phenotypically.
METHODS—Transgenic TPras mice (n=8) and normal, age matched control mice (n=6) were sacrificed at 3 weeks, 6 weeks, 7 weeks, 4 months, 5 months, 9 months, and 11 months. Six were processed in formalin for light microscopic examination and eight in a glutaraldehyde/formalin solution for electron microscopic examination.
RESULTS—Six of the TPras mice were found to have bilateral pigmented melanocytic/RPE proliferations of the uveal tract. The cytological characteristics of the tumours included low nuclear to cytoplasmic ratios (N:C ratios), bland nuclei, and abundant intracytoplasmic melanin. By EM two populations of cells were identified, including spindle-shaped cells with round to oval melanin granules and cuboidal cells with apically located, cigar-shaped, melanin granules, and basement membrane formation. A 3 week and an 11 month old TPras mouse had a higher grade, bilateral, melanocytic proliferation of the uveal tract which, although not metastatic, was morphologically melanoma. Cytological features included increased N:C ratios, nuclear pleomorphism, and prominent nucleoli. The uveal tract was normal in both eyes in all of the control animals.
CONCLUSION—Pigmented intraocular tumours developed in transgenic strains of mice that express a mutated Ha-ras gene in melanin producing cells. The morphology was most consistent with a melanoma in two of the mice and a benign melanocytic/RPE proliferation in the remaining mice.

 Keywords: histopathology; melanoma model; transgenic mice; uveal melanoma

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Figure 1  .

Figure 1  

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(A) Light micrograph of melanocytic hamartoma in the uveal tract of TPras transgenic mice. The melanocytic proliferation is seen to fill the entire uveal tract. Cells are deeply pigmented and morphological features are not readily discernible (haematoxylin and eosin, original magnification ×10). (B) High power light micrograph of the bleached specimen demonstrates the cytological characteristics of the melanocytic/RPE hamartoma with oval nuclei with bland nuclear characteristics (haematoxylin and eosin, original magnification ×10). Inset (C): Bleached specimen demonstrates a proliferation of plump polyhedral to spindle-shaped cells diffusely filling the uveal tract.

Figure 2  .

Figure 2  

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An electron micrograph of a melanocytic hamartoma in the uveal tract of TPras transgenic mice. Both spindle cells and cuboidal cells with oval nuclei containing marginated heterochromatin are identified. Intracytoplasmic membranous vesicles, premelanosomes, phagosomes, and cigar-shaped and oval melanin granules are identified. The melanosomes measure between 0.4 and 1.50 µm. Atypical nuclear features are identified in one cell (lower left) which contains a prominent nucleolus (original magnification ×5510).

Figure 3  .

Figure 3  

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(A) Light micrograph of melanoma in the uveal tract of TPras transgenic mice. The melanocytic proliferation is seen to fill the entire uveal tract. Cells are moderately pigmented and morphological features are not readily discernible (haematoxylin and eosin, original magnification ×10). (B) High power light micrograph of the bleached specimen demonstrates a proliferation of pleomorphic, spindle-shaped cells. The cytological characteristics of the malignant melanoma in the 3 week TPras mouse are demonstrated. (C) Ultrastructurally, the cells are spindle shaped with oval to round nuclei, increased nuclear to cytoplasmic ratios, marginated chromatin, irregular nuclear envelope, and prominent nucleoli. Intracytoplasmic melanin granules are demonstrated (haematoxylin and eosin, original magnification ×160).

Figure 4  .

Figure 4  

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(A) Photomicrograph of the anterior uveal tract in one of the control (negative littermate) mice. The iris ciliary body and choroid are pigmented and normal in structure. There is no evidence of infiltration hyperplasia or hypertrophy of the uveal tract (original magnification ×44). (B) Electron micrograph demonstrating the retinal/choroidal junction in one of the control mice. Choroidal melanocytes are spindle-shaped cells with oval nuclei containing a bland chromatin pattern. Intracytoplasmic round and oval melanin granules are identified. The melanosomes measure 0.50 µm by 0.75 µm. The RPE is composed of cuboidal cells with oval nuclei containing marginated heterochromatin. There is apical to basal polarity and basement membrane formation. Intracytoplasmic rough endoplasmic phagosomes and membranous vesicles are identified. Intracytoplasmic cigar-shaped and oval melanin granules are identified and measure 0.44 µm by 1.58 µm (original magnification ×9180).

Figure 5  .

Figure 5  

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(A) Light micrograph demonstrating a retinal pigment epithelial adenomatous proliferation found in the uveal tract of a normal control litter mate. (B) Histopathologically, this was characterised as a melanotic proliferation of RPE between the retina and the choroid. The cells were noted to form tubuloacinar configurations (haematoxylin and eosin, original magnification ×160).

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