Stem Cell Proliferation Is Kept in Check by the Chromatin Regulators Kismet/CHD7/CHD8 and Trr/MLL3/4.

Chromatin remodeling accompanies differentiation, however, its role in self-renewal is less well understood. We report that in Drosophila, the chromatin remodeler Kismet/CHD7/CHD8 limits intestinal stem cell (ISC) number and proliferation without affecting differentiation. Stem-cell-specific whole-genome profiling of Kismet revealed its enrichment at transcriptionally active regions bound by RNA polymerase II and Brahma, its recruitment to the transcription start site of activated genes and developmental enhancers and its depletion from regions bound by Polycomb, Histone H1, and heterochromatin Protein 1. We demonstrate that the Trithorax-related/MLL3/4 chromatin modifier regulates ISC proliferation, colocalizes extensively with Kismet throughout the ISC genome, and co-regulates genes in ISCs, including Cbl, a negative regulator of Epidermal Growth Factor Receptor (EGFR). Loss of kismet or trr leads to elevated levels of EGFR protein and signaling, thereby promoting ISC self-renewal. We propose that Kismet with Trr establishes a chromatin state that limits EGFR proliferative signaling, preventing tumor-like stem cell overgrowths

Overexpression of Partner of Numb Induces Asymmetric Distribution of the PI4P 5-Kinase Skittles in Mitotic Sensory Organ Precursor Cells in Drosophila

Unequal segregation of cell fate determinants at mitosis is a conserved mechanism whereby cell fate diversity can be generated during development. In Drosophila, each sensory organ precursor cell (SOP) divides asymmetrically to produce an anterior pIIb and a posterior pIIa cell. The Par6-aPKC complex localizes at the posterior pole of dividing SOPs and directs the actin-dependent localization of the cell fate determinants Numb, Partner of Numb (Pon) and Neuralized at the opposite pole. The plasma membrane lipid phosphatidylinositol (4,5)-bisphosphate (PIP2) regulates the plasma membrane localization and activity of various proteins, including several actin regulators, thereby modulating actin-based processes. Here, we have examined the distribution of PIP2 and of the PIP2-producing kinase Skittles (Sktl) in mitotic SOPs. Our analysis indicates that both Sktl and PIP2 reporters are uniformly distributed in mitotic SOPs. In the course of this study, we have observed that overexpression of full-length Pon or its localization domain (LD) fused to the Red Fluorescent Protein (RFP::PonLD) results in asymmetric distribution of Sktl and PIP2 reporters in dividing SOPs. Our observation that Pon overexpression alters polar protein distribution is relevant because RFP::PonLD is often used as a polarity marker in dividing progenitors

Drosophila

The Drosophila adult posterior midgut has been identified as a powerful system in which to study mechanisms that control intestinal maintenance, in normal conditions as well as during injury or infection. Early work on this system has established a model of tissue turnover based on the asymmetric division of intestinal stem cells. From the quantitative analysis of clonal fate data, we show that tissue turnover involves the neutral competition of symmetrically dividing stem cells. This competition leads to stem-cell loss and replacement, resulting in neutral drift dynamics of the clonal population. As well as providing new insight into the mechanisms regulating tissue self-renewal, these findings establish intriguing parallels with the mammalian system, and confirm Drosophila as a useful model for studying adult intestinal maintenance

Hair follicles’ transit-amplifying cells govern concurrent dermal adipocyte production through sonic hedgehog

Growth and regeneration of one tissue within an organ compels accommodative changes in the surrounding tissues. However, the molecular nature and operating logic governing these concurrent changes remain poorly defined. The dermal adipose layer expands concomitantly with hair follicle downgrowth, providing a paradigm for studying coordinated changes of surrounding lineages with a regenerating tissue. Here, we discover that hair follicle transit-amplifying cells (HF-TACs) play an essential role in orchestrating dermal adipogenesis through secreting Sonic Hedgehog (SHH). Depletion of Shh from HF-TACs abrogates both dermal adipogenesis and hair follicle growth. Using cell type-specific deletion of Smo, a gene required in SHH-receiving cells, we found that SHH does not act on hair follicles, adipocytes, endothelial cells, and hematopoietic cells for adipogenesis. Instead, SHH acts directly on adipocyte precursors, promoting their proliferation and their expression of a key adipogenic gene, peroxisome proliferator-activated receptor γ (Pparg), to induce dermal adipogenesis. Our study therefore uncovers a critical role for TACs in orchestrating the generation of both their own progeny and a neighboring lineage to achieve concomitant tissue production across lineages.ISSN:0890-9369ISSN:1549-547

Hair follicles’ transit-amplifying cells govern concurrent dermal adipocyte production through Sonic Hedgehog

Growth and regeneration of one tissue within an organ compels accommodative changes in the surrounding tissues. However, the molecular nature and operating logic governing these concurrent changes remain poorly defined. The dermal adipose layer expands concomitantly with hair follicle downgrowth, providing a paradigm for studying coordinated changes of surrounding lineages with a regenerating tissue. Here, we discover that hair follicle transit-amplifying cells (HF-TACs) play an essential role in orchestrating dermal adipogenesis through secreting Sonic Hedgehog (SHH). Depletion of Shh from HF-TACs abrogates both dermal adipogenesis and hair follicle growth. Using cell type-specific deletion of Smo, a gene required in SHH-receiving cells, we found that SHH does not act on hair follicles, adipocytes, endothelial cells, and hematopoietic cells for adipogenesis. Instead, SHH acts directly on adipocyte precursors, promoting their proliferation and their expression of a key adipogenic gene, peroxisome proliferator-activated receptor γ (Pparg), to induce dermal adipogenesis. Our study therefore uncovers a critical role for TACs in orchestrating the generation of both their own progeny and a neighboring lineage to achieve concomitant tissue production across lineages

Drosophila midgut homeostasis involves neutral competition between symmetrically dividing intestinal stem cells

The Drosophila adult posterior midgut has been identified as a powerful system in which to study mechanisms that control intestinal maintenance, in normal conditions as well as during injury or infection. Early work on this system has established a model of tissue turnover based on the asymmetric division of intestinal stem cells. From the quantitative analysis of clonal fate data, we show that tissue turnover involves the neutral competition of symmetrically dividing stem cells. This competition leads to stem-cell loss and replacement, resulting in neutral drift dynamics of the clonal population. As well as providing new insight into the mechanisms regulating tissue self-renewal, these findings establish intriguing parallels with the mammalian system, and confirm Drosophila as a useful model for studying adult intestinal maintenance

Spen limits intestinal stem cell self-renewal.

Precise regulation of stem cell self-renewal and differentiation properties is essential for tissue homeostasis. Using the adult Drosophila intestine to study molecular mechanisms controlling stem cell properties, we identify the gene split-ends (spen) in a genetic screen as a novel regulator of intestinal stem cell fate (ISC). Spen family genes encode conserved RNA recognition motif-containing proteins that are reported to have roles in RNA splicing and transcriptional regulation. We demonstrate that spen acts at multiple points in the ISC lineage with an ISC-intrinsic function in controlling early commitment events of the stem cells and functions in terminally differentiated cells to further limit the proliferation of ISCs. Using two-color cell sorting of stem cells and their daughters, we characterize spen-dependent changes in RNA abundance and exon usage and find potential key regulators downstream of spen. Our work identifies spen as an important regulator of adult stem cells in the Drosophila intestine, provides new insight to Spen-family protein functions, and may also shed light on Spen's mode of action in other developmental contexts

PIP2 Reporters and GFP::Sktl localized uniformly in SOPs in the absence of RFP::Pon^LD.

<p>The distribution of PH::GFP (A), ENTH::GFP (B) and GFP::Sktl (C–D″) was examined by live imaging (A–C) or by antibody staining (anti-GFP in green and anti-Senseless in red in D–D″) in dividing SOPs at prometaphase. When RFP::Pon^LD was not co-expressed in SOPs, the PIP2 reporters and GFP::Sktl (panel C; 100%; n = 20) localized uniformly. All transgenes were expressed under the control of neur^P72Gal4Gal80^ts.</p