Astrocytes, ependymal cells and the OPC-oligodendrocyte lineage are collectively referred to as macroglia. Oligodendrocyte precursor cells (OPCs) and mature oligodendrocytes (Olg) drive myelination in the vertebrate CNS, an evolutionary innovation that enabled rapid saltatory conduction and supported the emergence of larger, more complex brains.
The core OPC-Olg axis transcriptional program is detectable from teleost fishes to mammals, indicating a deeply conserved gliogenic module shared across jawed vertebrates.
Both OPC and Olg clusters are defined by transcription factors such as RFX3, MAFK, MITF, ETV1, AFF2, NR1D1, SATB1 and PAX6, a modular architecture repeatedly reused across phylogeny.
Lineage-associated differences manifest in program scores and state composition rather than program identity, with amniotes, and especially mammals, showing expanded and specialized subclusters.
Dedicated re-clustering of the oligodendroglial lineage resolves 27 OPC/Olg clusters, nested within the 2 OPC and 3 oligodendrocyte major-type clusters of the 43-cluster atlas-level annotation. Each cluster is named for its first-ranked transcription factor.
| Cluster | Marker TF |
|---|---|
| OPC_0 | MAFK |
| OPC_1 | ZNF618 |
| OPC_2 | RFX3 |
| OPC_3 | RFX3 |
| OPC_4 | RFX3 |
| OPC_5 | MAFK |
| OPC_6 | MITF |
| OPC_7 | ETV1 |
| OPC_8 | MITF |
| OPC_9 | MITF |
| OPC_10 | SATB1 |
| OPC_11 | ZNF618 |
| OPC_12 | NR1D1 |
| OPC_13 | PAX6 |
| OPC_14 | ETV1 |
| OPC_15 | MAFK |
| Cluster | Marker TF |
|---|---|
| Olg_0 | AFF2 |
| Olg_1 | RFX3 |
| Olg_2 | AFF2 |
| Olg_3 | RFX3 |
| Olg_4 | MITF |
| Olg_5 | ETV1 |
| Olg_6 | MITF |
| Olg_7 | RFX3 |
| Olg_8 | NR1D1 |
| Olg_9 | TULP4 |
| Olg_10 | AFF2 |
The repeated occurrence of RFX3-, AFF2-, MITF- and MAFK-associated states across both OPC and Olg compartments highlights transcription-factor modules reused throughout the lineage, while unique markers such as TULP4 (Olg_9) and PAX6 (OPC_13) mark more specialized states.
The enrichment of specific oligodendrocyte lineage cell types across vertebrate clades reveals a pattern of phased establishment and lineage-specific remodeling of myelination in the central nervous system. A complete oligodendrocyte lineage together with a basic myelin program is already assembled in early jawed vertebrates.
A complete oligodendrocyte lineage and a basic myelin program are present from early jawed vertebrates onward, with OPC-state cluster enrichment in teleost fishes (e.g., OPC_12, OPC_13) consistent with this timing. The course is not a monotonic staircase from immature to mature states.
Sea lamprey cells scored positively for OL/OPC-like programs but lacked the compact-myelin transcriptomic module, whereas shark cells provided the positive control, pointing to an ancient origin of the lineage program.
Additional cluster-level enrichments in amphibians and reptile/bird lineages reflect lineage-specific remodeling of state composition rather than a fixed ladder of newly added programs, with the mammalian-specific OPC_14_ETV1 pointing to a recent innovation.
A mammalian-specific precursor state, potentially fine-tuning myelination for complex, large-brained mammals.
Shark cells provided a positive control for the lamprey test of OL/OPC-like program presence.
Sea lamprey cells scored positively for OL/OPC-like programs but lacked the compact-myelin module.
The OPC/Olg lineage subclusters sit within the 2 OPC and 3 oligodendrocyte major clusters of the 43-cluster atlas annotation.
Consistent with the compositional reorganization of the lineage, the MPZ/(MPZ+PLP1) usage share was markedly higher in teleost fishes than in tetrapods, revealing a major myelin-program transition across the water-to-land divide.
Median MPZ/(MPZ+PLP1) usage share (n = 33 species).
Median MPZ/(MPZ+PLP1) usage share (n = 45 species).
Two-sided test of the teleost versus tetrapod difference.
Entered this test; the remainder lacked at least 50 OL-high cells.
The MPZ/P0-dominant usage profile is therefore characteristic of the teleost fishes sampled here. PLP1 is likewise highly expressed in the mature oligodendrocytes of fishes and ranks among the myelin markers with the highest cross-species conservation and state specificity, and no confirmed MPZ/P0 ortholog could be identified in the white-spotted bamboo shark of our sampling.
State-proportion comparisons across the major vertebrate lineages support a mature-state bias with a low transitional fraction in mammals, and a relative progenitor enrichment in teleost fishes compared with mammals. Because these proportions are not controlled for brain region, study batch or phylogenetic relatedness, they are reported here as descriptive biases, not as assessments of evolutionary rate.
Birds show the highest progenitor proportion of all lineages among the sampled species, a distinctive feature of avian state composition.
Mammals support a mature-state bias with a low transitional fraction, consistent with the myelination demands of large, complex brains.
Reptiles show a markedly reduced mature-state fraction, with turtle lineages transitional-biased and lizard lineages progenitor-biased.
This comparative framework disentangles ancestral mechanisms essential for myelination from more recent, lineage-specific elaborations that may support complex neural computation, and clarifies how glial cells co-evolve with neuronal complexity. Conserved molecular modules are repurposed through regulatory evolution, revealing how the diversification of oligodendrocyte precursor pools was a key mechanism in the iterative evolution of vertebrate brain complexity and computational efficiency.
Investigate the myelinating lineage and its evolutionary trajectory across all 100 species in the atlas.