Mgat4b mediated selective N-glycosyl modification regulates melanocyte development and melanoma progression [bulk RNA-seq]

Dysregulated melanocyte state transitions are a pivotal driver of melanoma development, highlighting the need to identify key regulators of these processes. Understanding these factors is key to know how normal melanocyte functions and shift towards initiation of melanoma. Our study identifies Mgat4b, a glycosyl transferase involved in selective N-glycan branching enriched in pigment progenitors, as a key regulator of directional melanocyte migration and establishment of Melanocyte stem cell (McSC) pool during early development in zebrafish and mammalian melanocytes. Single cell RNA sequencing analysis in zebrafish upon targeted disruption of Mgat4b reveals that a subset of melanocytes marked by aberrant galectin expression are impaired in migration and are lost. Lectin binding proteomic analysis reveals the glycosylation of key melanocyte proteins Gpnmb, Kit, and Tyrp1 to be under the control of Mgat4b. Additionally, mislocalization of Gamma catenin (Jup) explains the observed defects in cell adhesion and migration to be regulated by mgat4b but not its isozyme mgat4a. Our meta-analysis further revealed that melanoma patients with both the BrafV600E mutation and elevated Mgat4b levels have significantly worse survival outcomes compared to those with only the BrafV600E mutation. By leveraging the MAZERATI platform to model BrafV600E driver mutation in vivo, we show that Mgat4b mutant cells fail to aggregate and initiate tumors. Our study underscores the importance of selective N-glycan branching in both melanocyte development and melanoma initiation, suggesting a Mitf controlled Mgat4b as a promising therapeutic target for melanoma treatment. Overall design: To investigate the mechanisms that inhibit mutant cells from initiating melanoma in the absence of mgat4b, we utilized mature melanophores and melanoma cells from the skin of five zebrafish, including both MAZERATI wild-type and MAZERATI zebrafish carrying mgat4b mutations. We then performed gene expression profiling analysis using data obtained from RNA-seq of melanophores and melanoma cells from both the zebrafish (wild-type and m4b mut). Comparative gene expression analysis was performed for wild-type melanoma and melanophores, m4b mut melanoma and melanophores, wild-type and m4b mut melanoma.