382: How animal blood cells evolved from unicellular ancestors

Nagahata Y et al., PNAS - A transcriptome-driven reconstruction of blood cell evolution shows modern animal blood lineages arose by repurposing an ancestral unicellular toolkit. The study traces macrophage-like origins, a bilaterian mast/killer split, and later deuterostome/vertebrate innovations. Key terms: blood cell evolution, macrophage, mast cell, Fos, thymus.

Study Highlights:
The authors used cross-species transcriptomics and TF-focused phylogenies to show that the metazoan blood cell program traces to a premetazoan toolkit governed by Fos, producing macrophage-like initial blood cells. They infer a first major bifurcation at the origin of Bilateria that gave rise to a mast/killer lineage equipped with granular proteases specialized for antiparasitic defense. Deuterostome and vertebrate ancestors then diversified this mast lineage into T/NK and erythrocyte/thrombocyte branches while B cells emerged from the macrophage branch, and a prototypic thymus formed at tunicate gill edges. Murine hematopoiesis retains vestiges of this history: macrophage and mast potentials are widely preserved and ancient HSC-like progenitors persist.

Conclusion:
Blood cell diversity in animals represents a Fos-mediated repurposing of an ancestral unicellular program, with macrophage-like cells as the earliest blood lineage and subsequent bilaterian and deuterostome innovations producing mast/killer, lymphoid, and erythroid branches.

Music:
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Article title:
Animals have expanded the evolutionary legacy of unicellular ancestors in blood cells

First author:
Nagahata Y

Journal:
PNAS

DOI:
10.1073/pnas.2528110123

Reference:
Nagahata Y, Ishidae T, Satou Y, Nishimura Y, Kaitani R, Leong JCK, Oda-Ishiie I, Carmona-Rivas M, Najle SR, Ruiz-Trillo I, Kohtsuka H, Abeg S, Ikuta K, Miura T, Kawamoto H, Casacuberta E, Ogasawara M, Irieda N. Animals have expanded the evolutionary legacy of unicellular ancestors in blood cells. PNAS. 2026;123(23):e2528110123. doi:10.1073/pnas.2528110123

License:
This episode is based on an open-access article published under the Creative Commons Attribution 4.0 International License (CC BY 4.0) – https://creativecommons.org/licenses/by/4.0/

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Episode link: https://basebybase.com/episodes/base-by-base-382-blood-cell-evolution

QC:
This episode was checked against the original article PDF and publication metadata for the episode release published on 2026-06-02.

QC Scope:
- article metadata and core scientific claims from the narration
- excludes analogies, intro/outro, and music
- transcript coverage: Audited the spoken content describing the article’s core evolutionary timeline for blood cells, Fos-driven regulatory origins, macrophage-like ancestries, bilaterian mast/killer divergence, lineage branching to T/NK and erythrocyte/thrombocyte, B cell origin from macrophages, thymus evolution at gill edges, and implica
- transcript topics: Origin of blood cells at the metazoan root and Fos-driven premetazoan toolkit; Cross-species transcriptomics and transcription factor phylogeny; Macrophage-like primitive blood cells; Divergence of mast/killer lineage at Bilateria origin and granzyme-containing cells; Erythrocyte/thrombocyte lineage derived from mast/killer cells; B cells arising from macrophages

QC Summary:
- factual score: 10/10
- metadata score: 10/10
- supported core claims: 6
- claims flagged for review: 0
- metadata checks passed: 4
- metadata issues found: 0

Metadata Audited: