GEOapplication/xmlftp://ftp.ncbi.nlm.nih.gov/geo/series/GSE313nnn/GSE313637/primary200OKTranscriptomicsDanio rerioExpression profiling by high throughput sequencinghttps://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE313637GEOGSEfalseCellular composition of zebrafish spleen melanomacrophage centresAntibody affinity maturation in mammals occurs in germinal centers (GCs), supported by follicular dendritic cells (FDCs) and T follicular helper (Tfh) cells. Teleost fish lack GCs, and their melanomacrophage centres (MMCs) have been proposed as functional analogues; however, the presence of FDCs remains uncertain. To define MMC cellular composition, we isolated autofluorescent MMCs from zebrafish spleens and performed single-cell RNA sequencing (scRNA-seq) on 13,632 cells. Clustering and marker-based annotation identified centroblast-like and memory-like B cells, cytotoxic and memory CD8+ T cells, Th2/Tfh-like CD4+ T cells, and melanomacrophages with features of marginal zone and tingible body macrophages. Importantly, a progenitor fibroblastic reticular cell (pFRC)-like population expressed high levels of FDC-associated markers (mfge8, clu, vcam1, tnfsf13b, cxcl12), suggesting it may serve as an FDC analogue. Chemokine gene expression analysis highlighted a dominant CXCR4-CXCL12 axis, with pFRC-like cells expressing cxcl12 and ccl25 to potentially attract B and T cells, while lymphocyte subsets expressed corresponding receptors. Together, these data support a model in which melanomacrophages and pFRC-like cells mediate antigen presentation and B-cell selection, while Th2/Tfh-like cells provide survival signals. Thus, zebrafish MMCs meet the cellular requirements to enable affinity maturation, and define a primitive analogue of germinal centers2026/09/23GSE313637GSM937139625922313637Danio rerio[42740903]