RNA-seq analysis identifies different transcriptomic types and developmental trajectories of primary melanomas.

Area of Science:

• Genomics
• Molecular Biology
• Dermatology

Background:

• Understanding gene expression changes during melanoma development is crucial but less understood than mutational events.
• Early melanomagenesis involves complex molecular alterations that require comprehensive analysis.

Purpose of the Study:

• To characterize molecular mechanisms of early melanoma development using RNA-sequencing.
• To identify distinct transcriptomic profiles of melanocytic nevi and primary melanomas.
• To explore evolutionary trajectories and immune-escape mechanisms in melanoma progression.

Main Methods:

• Comprehensive RNA-sequencing of laser-microdissected melanocytic nevi (n=23) and primary melanoma samples (n=57).
• Application of self-organizing maps, unsupervised clustering, and pseudotime (PT) dynamics analysis.
• Characterization of mutational landscapes (NRAS, BRAF) and gene signatures (MITF, AXL).

Main Results:

• Identified two transcriptomic types of nevi (N1, N2) and melanomas (M1, M2).
• N1/M1 lesions show pigmentation/MITF signatures with NRAS mutations; N2/M2 lesions show inflammatory/AXL signatures with varied BRAF/NRAS mutations.
• M1 melanomas exhibit BRAF/MEK inhibitor resistance signatures; M2 melanomas show anti-PD-1 resistance signatures.
• Pseudotime analysis suggests a switch-like immune-escape mechanism involving immune gene downregulation and cell cycle gene upregulation in late-stage melanomas.

Conclusions:

• Transcriptome analysis provides critical gene signatures and mechanisms for early and late-stage melanoma development.
• Findings have implications for melanoma diagnostics and therapeutic strategies.
• Distinct molecular subtypes identified may guide personalized treatment approaches.