Histone variant dictates fate biasing of neural crest cells to melanocyte lineage

Abstract

In the neural crest lineage, progressive fate restriction and stem cell assignment are crucial for both development and regeneration. Whereas fate commitment events have distinct transcriptional footprints, fate biasing is often transitory and metastable, and is thought to be moulded by epigenetic programmes. Therefore, the molecular basis of specification is difficult to define. In this study, we established a role for a histone variant, H2a.z.2, in specification of the melanocyte lineage from multipotent neural crest cells. H2a.z.2 silencing reduces the number of melanocyte precursors in developing zebrafish embryos and from mouse embryonic stem cells in vitro. We demonstrate that this histone variant occupies nucleosomes in the promoter of the key melanocyte determinant mitf, and enhances its induction. CRISPR/Cas9-based targeted mutagenesis of this gene in zebrafish drastically reduces adult melanocytes, as well as their regeneration. Thereby, our study establishes the role of a histone variant upstream of the core gene regulatory network in the neural crest lineage. This epigenetic mark is a key determinant of cell fate and facilitates gene activation by external instructive signals, thereby establishing melanocyte fate identity.

Identification of chromatin states during zebrafish gastrulation using CUT&RUN and CUT&Tag

“…This shifting H2A.Z landscape suggests genomic H2A.Z reorganization may help drive differentiation over this developmental window. Consistent with this model, prior studies indicate that disruption of H2A.Z over similar developmental periods in zebrafish and frog embryos leads to defects in neural crest derived tissues (Greenberg et al, 2019; Raja et al, 2020).…”

Histone variants at a glance

“…Chordates encode two H2A.Z proteins (Eirín-López et al, 2009), H2A.Z.1 and H2A.Z.2, which differ by three conserved amino acids (reviewed in Cheema et al, 2020). H2A.Z.1-knockout animals die during early development (Faast et al, 2001) and H2A.Z.2 is required for melanocyte development in zebrafish (Raja et al, 2020). In humans, H2A.Z.1 and H2A.Z.2 have qualitatively similar, but quantitatively different, expression patterns, with a subset of H2A.Z.2-biased enhancers affecting genes that are downregulated in the cranio-facial abnormality disease floating harbor syndrome (Greenberg et al, 2019).…”

Epigenetic regulation during melanocyte development and homeostasis

“…For example, the regular H3. 94 . This suggested that h2a.z.2 plays a specific role in establishing the melanocyte and glia derivatives of the crest 94,96 .…”

“…94 . This suggested that h2a.z.2 plays a specific role in establishing the melanocyte and glia derivatives of the crest 94,96 . Chromatin immunoprecipitation experiments showed that H2a.z.2 occupied the mitf-a promoter and induced mitf-a expression by modulating the accessibility of the promoter in zebrafish as well as in B16 mouse melanoma cells 94 .…”

“…In contrast to the effects observed with h2.a.z.2 knockdown in zebrafish, h2a.z.2 morpolino-injected tadpoles were more heavily pigmented than h2a.z.1 injected tadpoles 95 ; this effect was not compared to respective controls. This suggests that H2a.z.2 might be playing a different role in regulating pigmentation in frogs than in zebrafish where the expression of h2a.z.2 is essential for all stages of melanocyte development 94 .…”