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A Hedgehog-Induced Homeodomain Cascade Couples Progenitor Identity to Neuronal Diversification

ABSTRACT: How progenitor identity instructs neuronal diversification remains unclear. We uncover a homeodomain transcription factor (HDTF) cascade that links the identity of a single lamina progenitor type to the diversification of all five lamina neuron subtypes in the Drosophila visual system. Hedgehog signaling induces a pan-class HDTF—expressed across all subtypes of a neuronal class, here all lamina neurons—in progenitors, promoting cell-cycle exit. This progenitor-derived pan-class HDTF is inherited by newborn lamina neurons, where it activates subtype-specific, differentially expressed (DE) HDTFs and acts combinatorially with these DE-HDTFs to specify distinct neuronal subtypes. Loss of DE-HDTFs induces predictable, subtype-specific fate conversions—morphological and functional—reducing neuronal diversity. Strikingly, we find mouse retinal neurons express analogous pan-class and DE-HDTFs, indicating an evolutionarily conserved strategy. With HDTFs broadly expressed, our findings define a progenitor-to-newborn HDTF cascade that provides a generalizable mechanism by which progenitor identity drives neuronal diversification from a limited progenitor pool.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE305551 | GEO | 2025/08/25

REPOSITORIES: GEO

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Project description:In most metazoan nuclei, heterochromatin is located at the nuclear periphery in contact with the nuclear lamina, which provides mechanical stability to the nucleus. We show that in cultured cells, chromatin de-compaction by the nucleosome binding protein HMGN5 decreases the sturdiness, elasticity, and rigidity of the nucleus. Mice overexpressing HMGN5, either globally or only in the heart, are normal at birth but develop hypertrophic heart with large cardiomyoctyes, deformed nuclei and disrupted lamina, and die of cardiac malfunction. Chromatin de-compaction is seen in cardiomyocytes of newborn mice but misshaped nuclei with disrupted lamina are seen only in adult cardiomyocytes, suggesting that loss of heterochromatin diminishes the ability of the nucleus to withstand the mechanical forces of the contracting heart. Thus, heterochromatin enhances the ability of the nuclear lamina to maintain the sturdiness and shape of the eukaryotic nucleus; a structural role for chromatin that is distinct from its genetic functions. The full length mouse Hmgn5 cDNA, containing the entire 5’ UTR and FLAG tag on the 3’ end was amplified by PCR and inserted between BglII and XhoI sites of the pCALL vector (Novak et al., 2000). This vector contains a floxed LacZ cDNA driven by the CAG (a hybrid CMV enhancer and chicken beta–actin) promoter which is highly active in early mouse embryos. The vector was linearized by NotI digestion and injected into fertilized oocytes of C57BL/6 mice. Total embryonic excision of LacZ sequence was done by breeding floxed HMGN5-TG mice with SoxCre mice (Hayashi et al., 2002). Heart-specific excision was performed by breeding floxed HMGN5-TG mice with alphaMHC-cre mice (Oka et al., 2006).Total RNA from the left ventricle of newborn and adult Hmgn5-hTG mice which overexpress HMGN5 only in the heart as well as control mice was collected from biological triplicates (duplicates, in the case of newborn wild-type mice) and analyzed by Affymetrix expression arrays.

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A Hedgehog-Induced Homeodomain Cascade Couples Progenitor Identity to Neuronal Diversification

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