Uncovering minimal pathways in melanoma initiation

Area of Science:

• Oncology
• Genetics
• Cell Biology

Background:

• Melanomas exhibit genetic heterogeneity, often involving mitogen-activated protein kinase mutations and tumor suppressor gene loss.
• Mouse models with combined mutations develop fast-growing tumors, unlike rare slow-growing tumors from Braf activation and Pten loss.

Purpose of the Study:

• To investigate the origins of slow-growing melanomas in mice with only a Braf mutation.
• To identify cellular precursors contributing to melanoma heterogeneity.

Main Methods:

• Induction of melanomas in albino mice with a Braf mutation.
• Analysis of tumor incidence kinetics and genomic stability.
• Single-cell transcriptomic analysis of tumors and normal skin.
• Gene expression analysis of identified cell populations.

Main Results:

• Slow-growing melanomas can arise in mice with only a Braf mutation, with incidence kinetics suggesting a stochastic event.
• No de novo mutations or structural variants were found to explain most tumor occurrences.
• A distinct cell population resembling neural crest-like cells was identified in normal skin and tumors.
• These neural crest-like cells expand upon Braf activation and persist through transplantation, acting as malignant cell precursors.

Conclusions:

• A Braf mutation alone can initiate melanoma development through a stochastic process.
• Neural crest-like cells in normal skin serve as precursors for malignant melanoma.
• This precursor state represents a slow path to malignancy and a potential source of tumor heterogeneity for therapeutic targeting.