Gilgamesh (Gish)/CK1γ regulates tissue homeostasis and aging in adult Drosophila midgut

Inter-cell type interactions that control JNK signaling in the Drosophila intestine

JNK signaling is a critical regulator of inflammation and regeneration, but how it is controlled in specific tissue contexts remains unclear. Here we show that, in the Drosophila intestine, the TNF-type ligand, Eiger (Egr), is expressed exclusively by intestinal stem cells (ISCs) and enteroblasts (EBs), where it is induced by stress and during aging. Egr preferentially activates JNK signaling in a paracrine fashion in differentiated enterocytes (ECs) via its receptor, Grindelwald (Grnd). N-glycosylation genes (Alg3, Alg9) restrain this activation, and stress-induced downregulation of Alg3 and Alg9 correlates with JNK activation, suggesting a regulatory switch. JNK activity in ECs induces expression of the intermembrane protease Rhomboid (Rho), driving secretion of EGFR ligands Keren (Krn) and Spitz (Spi), which in turn activate EGFR signaling in progenitor cells (ISCs and EBs) to stimulate their growth and division, as well as to produce more Egr. This study uncovers an N-glycosylation-controlled, paracrine JNK-EGFR-JNK feedforward loop that sustains ISC proliferation during stress-induced gut regeneration.

Wnt signaling couples G2 phase control with differentiation during hematopoiesis in Drosophila

During homeostasis, a critical balance is maintained between myeloid-like progenitors and their differentiated progeny, which function to mitigate stress and innate immune challenges. The molecular mechanisms that help achieve this balance are not fully understood. Using genetic dissection in Drosophila, we show that a Wnt6/EGFR-signaling network simultaneously controls progenitor growth, proliferation, and differentiation. Unlike G1-quiescence of stem cells, hematopoietic progenitors are blocked in G2 phase by a β-catenin-independent (Wnt/STOP) Wnt6 pathway that restricts Cdc25 nuclear entry and promotes cell growth. Canonical β-catenin-dependent Wnt6 signaling is spatially confined to mature progenitors through localized activation of the tyrosine kinases EGFR and Abelson kinase (Abl), which promote nuclear entry of β-catenin and facilitate exit from G2. This strategy combines transcription-dependent and -independent forms of both Wnt6 and EGFR pathways to create a direct link between cell-cycle control and differentiation. This unique combinatorial strategy employing conserved components may underlie homeostatic balance and stress response in mammalian hematopoiesis.

The zinc finger protein CG12744 regulates intestinal stem cells in aged Drosophila through the EGFR and BMP pathways

AIM

Aging is a process characterized by a time-dependent decline in the functionality of adult stem cells and is closely associated with age-related diseases. However, understanding how aging promotes disease and its underlying causes is critical for combating aging.

MAIN METHODS

The offspring of UAS-Gal4 and CG12744RNAiDrosophila were cultured for 33 days to evaluate the role of CG12744 in the aging intestine. Immunofluorescence was performed to detect specific cell type markers for assessing proliferation and differentiation. qRT-PCR was used to observe the changes in signaling regulating intestinal homeostasis in the aging intestine after CG12744 knockdown. 16S rRNA-seq analysis was also conducted to elucidate the role of gut microbes in CG12744-mediated intestinal dysfunction.

KEY FINDINGS

The mRNA levels of CG12744 were significantly increased in the aged midguts. Knockdown of CG12744 in progenitor cells further exacerbates the age-related intestinal hyperplasia and dysfunction. In particular, upon depletion of CG12744 in progenitors, enteroblasts (EBs) exhibited an increased propensity to differentiate along the enteroendocrine cell (EE) lineage. In contrast, the overexpression of CG12744 in progenitor cells restrained age-related gut hyperplasia in Drosophila. Moreover, CG12744 prevented age-related intestinal stem cell (ISC) overproliferation and differentiation by modulating the EGFR, JNK, and BMP pathways. In addition, the inhibition of CG12744 resulted in a significant increase in the gut microbial composition in aging flies.

SIGNIFICANCE

This study established a role for the CG12744 in regulating the proliferation and differentiation of adult stem cells, thereby identifying a potential therapeutic target for diseases caused by age-related dysfunction stem cell dysfunction.

Protein proximity networks and functional evaluation of the casein kinase 1 gamma family reveal unique roles for CK1γ3 in WNT signaling

Aberrant activation or suppression of WNT/β-catenin signaling contributes to cancer initiation and progression, neurodegeneration, and bone disease. However, despite great need and more than 40 years of research, targeted therapies for the WNT pathway have yet to be fully realized. Kinases are considered exceptionally druggable and occupy key nodes within the WNT signaling network, but several pathway-relevant kinases remain understudied and "dark." Here, we studied the function of the casein kinase 1γ (CSNK1γ) subfamily of human kinases and their roles in WNT signaling. miniTurbo-based proximity biotinylation and mass spectrometry analysis of CSNK1γ1, CSNK1γ2, and CSNK1γ3 revealed numerous components of the β-catenin-dependent and β-catenin-independent WNT pathways. In gain-of-function experiments, we found that CSNK1γ3 but not CSNK1γ1 or CSNK1γ2 activated β-catenin-dependent WNT signaling, with minimal effect on other signaling pathways. We also show that within the family, CSNK1γ3 expression uniquely induced low-density lipoprotein receptor-related protein 6 phosphorylation, which mediates downstream WNT signaling transduction. Conversely, siRNA-mediated silencing of CSNK1γ3 alone had no impact on WNT signaling, though cosilencing of all three family members decreased WNT pathway activity. Finally, we characterized two moderately selective and potent small-molecule inhibitors of the CSNK1γ family. We show that these inhibitors and a CSNK1γ3 kinase-dead mutant suppressed but did not eliminate WNT-driven low-density lipoprotein receptor-related protein 6 phosphorylation and β-catenin stabilization. Our data suggest that while CSNK1γ3 expression uniquely drives pathway activity, potential functional redundancy within the family necessitates loss of all three family members to suppress the WNT signaling pathway.