CD34 defines melanocyte stem cell subpopulations with distinct regenerative properties

Melanocyte stem cells (McSCs) are the undifferentiated melanocytic cells of the mammalian hair follicle (HF) responsible for recurrent generation of a large number of differentiated melanocytes during each HF cycle. HF McSCs reside in both the CD34+ bulge/lower permanent portion (LPP) and the CD34- secondary hair germ (SHG) regions of the HF during telogen. Using Dct-H2BGFP mice, we separate bulge/LPP and SHG McSCs using FACS with GFP and anti-CD34 to show that these two subsets of McSCs are functionally distinct. Genome-wide expression profiling results support the distinct nature of these populations, with CD34- McSCs exhibiting higher expression of melanocyte differentiation genes and with CD34+ McSCs demonstrating a profile more consistent with a neural crest stem cell. In culture and in vivo, CD34- McSCs regenerate pigmentation more efficiently whereas CD34+ McSCs selectively exhibit the ability to myelinate neurons. CD34+ McSCs, and their counterparts in human skin, may be useful for myelinating neurons in vivo, leading to new therapeutic opportunities for demyelinating diseases and traumatic nerve injury.

Heterogeneous tumor subpopulations cooperate to drive invasion

Clonal selection and transcriptional reprogramming (e.g., epithelial-mesenchymal transition or phenotype switching) are the predominant theories thought to underlie tumor progression. However, a "division of labor" leading to cooperation among tumor-cell subpopulations could be an additional catalyst of progression. Using a zebrafish-melanoma xenograft model, we found that in a heterogeneous setting, inherently invasive cells, which possess protease activity and deposit extracellular matrix (ECM), co-invade with subpopulations of poorly invasive cells, a phenomenon we term "cooperative invasion". Whereas the poorly invasive cells benefit from heterogeneity, the invasive cells switch from protease-independent to an MT1-MMP-dependent mode of invasion. We did not observe changes in expression of the melanoma phenotype determinant MITF during cooperative invasion, thus ruling out the necessity for phenotype switching for invasion. Altogether, our data suggest that cooperation can drive melanoma progression without the need for clonal selection or phenotype switching and can account for the preservation of heterogeneity seen throughout tumor progression.

Photobiology of ocular melanocytes and melanoma

There are two different types of ocular melanocytes and melanomas. Conjunctival melanocytes are located on the surface of the eye and are exposed to visible light and UV radiation. Recently, epidemiological studies demonstrated that sunlight plays a definite role in the occurrence of conjunctival melanoma, as it does in cutaneous melanoma. Uveal melanocytes consist of the iridal melanocytes, which are exposed to visible light and UV radiation; and the ciliary body melanocytes and choroidal melanocytes, which are not exposed to light radiation. Epidemiological studies demonstrated that sunlight may play a role in the occurrence of iridal melanoma, but may not be a major factor in the etiology of ciliary body and choroidal melanomas. Uveal melanocytes differ from epidermal melanocytes in that epidermal melanocytes respond to UV radiation and skin color becomes darker after exposure to sunlight; but uveal melanocytes do not respond to UV radiation and the iris color remains stable after exposure to sunlight. Recently, in vitro studies indicate that this phenomenon is determined both by cellular factors and environmental factors.

Lumbar spinal meningeal melanocytoma of the l3 nerve root with paraspinal extension: a case report

STUDY DESIGN

A case report of spinal meningeal melanocytoma with a dumbbell-shaped extension and its magnetic resonance imaging features is presented.

OBJECTIVE

To present a rare spinal tumor with pathologic and radiologic features.

SUMMARY OF BACKGROUND DATA

Meningeal melanocytomas are rare lesions usually found in the posterior fossa and upper cervical spine. The review of literature shows the variation in different studies. The characteristic magnetic resonance imaging features of meningeal melanocytoma have not yet been defined.

METHODS

A 33-year-old woman presented with a 3-year history of backache and weakness of her left lower limb. Magnetic resonance imaging showed a large dumbbell tumor at L3-L4 with extension in the paraspinal region. Schwannoma was the first possibility suggested by the MRI features. Histopathology of the lesion showed a meningeal melanocytoma.

RESULTS

The patient showed a significant recovery after surgery and a full course of radiotherapy.

CONCLUSIONS

Radiologic presentation could be confusing in cases of spinal dumbbell-shaped tumors. Awareness of the lesion characteristics will facilitate diagnosis and treatment of this condition.

Studies on epidermis reconstructed with and without melanocytes: melanocytes prevent sunburn cell formation but not appearance of DNA damaged cells in fair-skinned caucasians

To assess the photoprotective role of melanocytes in the epidermis, we studied the effects of ultraviolet B on an epidermis reconstructed with and without melanocytes. To address more specifically the role of melanin in fair-skinned individuals, experiments were done with cells obtained from human skin of low phototypes (II-III). To study the effect of constitutive melanin and possibly that of newly synthesized melanin precursors, a single dose of ultraviolet B (0.10 or 0.15 J per cm2, corresponding to a 4-5 minimal erythema dose in vivo) was administered to reconstructs and the effects were monitored over the first 24 h. When reconstructs with and without melanocytes were compared, no difference was found for DNA damage/repair assessed with antibodies to cyclobutane pyrimidine dimers and 6-4 photoproducts. More necrotic/apoptotic cells, however, were noted 24 h following ultraviolet B irradiation in reconstructs lacking melanocytes. Twenty-four hours following ultraviolet B irradiation the number of necrotic/apoptotic cells and the number of cyclobutane pyrimidine dimer positive cells was coarsely concentration-dependent. The number of cyclobutane pyrimidine dimer positive cells, however, was independent of the type of reconstruct used (with/without melanocytes). In conclusion, low phototype melanocytes seem to protect epidermal basal cells against ultraviolet B-induced apoptosis/necrosis and may preserve the overall integrity of the epidermis after ultraviolet B irradiation. On the contrary, such melanocytes do not seem to have a protective role against DNA damage and may not prevent cancer.

Indeterminate melanocytic proliferations of the conjunctiva

OBJECTIVE

To test the hypothesis that a subset of conjunctival melanocytic proliferations exists that cannot be reproducibly classified as benign, malignant, or indeterminate.

METHODS

Three groups of excisional biopsy specimens of conjunctival melanocytic proliferations were evaluated by a panel of 5 ophthalmic pathologists. These groups included lesions that we considered to represent benign (group 1 [n = 5]), malignant (group 2 [n = 5]), and indeterminate melanocytic proliferations (group 3 [n = 5]). The panel classified the same sections in all 3 groups in a randomized, masked fashion, first without and then with a clinical history of patient age, sex, and race. The kappa statistic was used to quantify the degree of agreement among observers.

RESULTS

There was strong concordance among the panel members for both group 1 (benign [kappa = 0.76]) and group 2 (malignant [kappa = 0.70]) melanocytic proliferations. There was no concordance of the panel for group 3 (indeterminate) lesions (kappa = -0.045). The concordance for groups 1 and 2 and lack of concordance for group 3 lesions were independent of knowledge of clinical history of age, sex, and race.

CONCLUSION

A subset of melanocytic proliferations of the conjunctiva exists that cannot be reproducibly classified by pathologists as benign, malignant, or indeterminate.

Abnormal melanosomes: ultrastructural markers of melanocytic atypia

To identify possible ultrastructural markers of melanocytic atypia, a quantitative ultrastructural study was made of melanocytes found at the dermal-epidermal boundary of normal skin and in benign, premalignant, and malignant melanocytic lesions. There was a significant increase (p < 0.05) in the number of melanosomes per melanocyte in the premalignant and malignant lesions compared with the number observed in the benign lesions. There was a significantly higher number (p < 0.05) of abnormal melanosomes (with irregularities in the laminar matrix or with a granular or clumpy matrix) in the premalignant and malignant lesions, which suggests that the presence of a high percentage of abnormal melanosomes might act as a useful ultrastructural marker in the diagnosis of melanocytic atypia.

Antigen-presenting OKM5+ melanophages appear in human epidermis after ultraviolet radiation

Ultraviolet radiation of murine skin in vivo or epidermal cells (EC) in vitro dramatically inhibits the antigen-presenting capacity of EC in vitro and results in the inhibition of immune responses to antigen challenge. In humans, UV exposure in vivo markedly inhibits alloantigen presentation by EC in the EC-lymphocyte reaction (ELR) when EC are harvested immediately after the administration of 4 times the minimal erythema dose (4 MED), whereas EC harvested 72 h after 4 MED (UV-EC) exhibit enhanced allostimulatory capacity in the ELR. This enhanced ELR reactivity is due to the appearance, in the epidermis, of bone marrow-derived OKT6- DR+ cells which are distinct from Langerhans cells (LC) in their lack of surface OKT6 and in their ultrastructural morphology. This report focuses on the phenotype and function of T6- Dr+ UV-EC and on their relationship to known human antigen presenting cell (APC) subsets. Approximately 60% of T6- Dr+ UV-EC bore the monocyte marker defined by monoclonal antibody OKM5, but lacked determinants recognized by OKM1, Leu M1, Leu M3, Leu M4, Leu M5, and Mac1. All T6- Dr+ UV-EC bore the class II MHC antigen HLA-DQ (DC/DS), which is associated with a specialized subset of antigen-presenting monocytes capable of stimulation in the autologous mixed leukocyte reaction (AMLR). Panning of OKM5+ UV-EC resulted in a population of cells which was markedly enriched in melanophages and which exhibited potent alloantigen-presenting capacity in the ELR. Since OKM5+ T6- Dr+ UV-EC were similar to the specialized APC minor subset of OKM1- OKM5+ blood monocytes both in phenotype and in apparent phagocytic function, we examined other APC functions of UV-EC to assess the extent of this analogy. Relative to control EC (containing only LC as APC), UV-EC (containing functionally inactivated LC but many T6- Dr+ APC) induced significantly greater degrees of T-cell proliferation in the presence of either tetanus toxoid antigen or the mitogen concanavalin A. UV-EC, as well as panning-purified OKM5+ UV-EC, were also able to induce autologous T-cell proliferation in the absence of added antigen (autologous ELR), in contrast to control EC which were poor stimulators of an autologous ELR. Thus, although human EC 72 h after UV exposure are numerically and functionally depleted of LC, at least 2 additional subsets of T6- Dr+ APC appear in the epidermis.(ABSTRACT TRUNCATED AT 400 WORDS)