Pigment producing melanocytes as the cells of origin of BRAFV600E-induced mouse cutaneous melanoma

To investigate whether cutaneous melanoma originates from a resident adult melanocyte stem cell (MSC) or a mature melanocyte, we created a model that recapitulates key histopathological features of human melanomagenesis by inducing a BRafV600E-driven melanomagenic program in interfollicular (IF) melanocytes located in mouse tails.To this end, we sequenced the transcriptome of FACS-sorted individual IFE reporter-positive cells from BRaf/Pten/tdTomato mice, the tails of which had been painted with 4-HT for 31 and 72 days, respectively. These time points were chosen as melanoma cells are exclusively found in the IF epidermis at day 31 (d31) and in both epidermis and dermis at day 72 (d72). Normal IF melanocytes from Tyr::CreERT2/+; ROSA26RLSL-tdTomato/+ were also isolated and profiledThese data indicated that loss of differentiation markers occurs in a subset of targeted epidermal melanoma cells before the onset of dermal invasion and that this event may, at least partly, be a consequence of induction of Zeb1 expression.

为探究皮肤黑色素瘤（cutaneous melanoma）究竟起源于成体驻留黑素细胞干细胞（melanocyte stem cell, MSC）还是成熟黑素细胞，我们构建了一款实验模型。该模型通过在小鼠尾部的毛囊间（interfollicular, IF）黑素细胞中诱导BRAFV600E驱动的黑素瘤发生程序，重现了人类黑素瘤发生过程的关键组织病理学特征。为此，我们对经4-羟基他莫昔芬（4-HT）分别处理31天、72天的BRAF/Pten/tdTomato小鼠，通过荧光激活细胞分选（fluorescence-activated cell sorting, FACS）分离其单个毛囊间表皮（interfollicular epidermis, IFE）报告基因阳性细胞，并对其转录组进行测序。选取这两个时间点的依据为：第31天（d31）时，黑素瘤细胞仅存在于毛囊间表皮中；而第72天（d72）时，黑素瘤细胞同时分布于表皮与真皮内。我们同时分离并转录组分析了来自Tyr::CreERT2/+; ROSA26RLSL-tdTomato/+小鼠的正常毛囊间黑素细胞。本数据集的分析结果显示，在真皮侵袭启动前，部分靶向表皮来源的黑素瘤细胞会出现分化标志物丢失现象，且该事件至少部分由ZEB1表达诱导所介导。