Effects of Monoclonal Anti-c-Kit Antibody (ACK2) on Melanocytes in Newborn Mice

Abstract

Previous studies indicate that c-Kit is required for postnatal melanocyte development. To understand the precise mechanisms of c-Kit dependence, we studied melanocyte development in newborn C57BL/6 mice by means of peritoneal injection of a monoclonal anti-c-Kit antibody (ACK2), which blocks c-Kit functions. The mice were injected once or more with ACK2 at various intervals after birth. In experiment 1, skin samples were examined on day 10 post-partum and in experiment 2 they were examined daily until day 10 post-partum. We studied melanocytes in the hair follicles, epidermis, and dermis by light and electron microscopy with dopa reactions and immunohistochemistry. Epidermal melanocytes in untreated mice were dopa negative and c-Kit positive on day 0 post-partum but became dopa positive soon thereafter. In ACK2-treated mice, the earlier the mice received ACK2 injections after birth, the fewer melanocytes they had, not only in the epidermis, but also in follicles. In these mice, melanocytes that had undergone apoptosis in the dermis and the follicles were detected ultrastructurally. Some appeared to have produced tyrosinase, because they had dopa-positive melanosomes. These results suggest that melanocytes in newborn mice are c-Kit dependent and undergo apoptosis when c-Kit receptors are blocked by ACK2 in the early days after birth. During this c-Kit-dependent period, melanocytes differentiate from dopa negative to positive and migrate from the epidermis to hair follicles.

Bi-compartmental communication contributes to the opposite proliferative behavior of Notch1-deficient hair follicle and epidermal keratinocytes

“…melanocytes within the hair follicles) to be identified. Nonetheless, reduced autocrine Kitl does not contribute to the Notch1-deficient follicular phenotypes, because animals treated with ACK2 (anti c-Kit antibody) or animals with mutations that reduced Kitl levels do not display any phenotypes reminiscent of Notch1 loss in their hair follicles (Besmer et al, 1993;Botchkareva et al, 2001;Lecoin et al, 1995;Okura et al, 1995). To our knowledge, this is also the first report to place Notch1 upstream of Tgf␤ signaling in any cell type.…”

c-Kit-Targeting Immunotherapy for Hereditary Melanoma in a Mouse Model

“…We showed previously that both innate c-Ret and RET in RET-transgenic mice are transiently expressed at high levels soon after birth in association with primary hair growth (6,17). c-Kit was also reported to be expressed in melanocytes in skin soon after birth (22). We compared the levels of c-Kit expression in skin of RET-transgenic and littermate nontransgenic mice soon after birth.…”

“…1, A and C). It is known that c-Kit function is required for both melanocyte entry into the epidermal layer during midgestation and for melanocyte activation linked to the hair growth cycle during the postnatal phase (9,22). The c-Kit Wv protein is indistinguishable from normal c-Kit protein with regard to size and cell surface expression, but its in vitro kinase activity is ϳ10 -20% of that in ϩ/ϩ cells (8).…”

“…On the basis of the above-described observation that c-Kit, of which the expression is enhanced by RET soon after birth, basically assists RET to develop melanoma, we examined the therapeutic effect of injection of a monoclonal ACK2 (9,22) into line 304/B6 RET-transgenic mice soon after birth on melanoma development. It was unexpectedly found that melanoma development was long lastingly suppressed in RETtransgenic mice that received a single postnatal ACK2 injection within 12 months after the ACK2 injection (Fig.…”

Temporal and cellular requirements for Fms signaling during zebrafish adult pigment pattern development

“…11B) (Cable et al, 1995;Okura et al, 1995;Ito et al, 1999) and during the differentiation of zebrafish melanoblasts into melanophores in the regenerating fin ).…”