Growth factor independent-1 maintains Notch1-dependent transcriptional programming of lymphoid precursors

Transcriptional network dynamics in early T cell development

The rate at which cells enter the T cell pathway depends not only on the immigration of hematopoietic precursors into the strong Notch signaling environment of the thymus but also on the kinetics with which each individual precursor cell reaches T-lineage commitment once it arrives. Notch triggers a complex, multistep gene regulatory network in the cells in which the steps are stereotyped but the transition speeds between steps are variable. Progenitor-associated transcription factors delay T-lineage differentiation even while Notch-induced transcription factors within the same cells push differentiation forward. Progress depends on regulator cross-repression, on breaching chromatin barriers, and on shifting, competitive collaborations between stage-specific and stably expressed transcription factors, as reviewed here.

Multi-modular structure of the gene regulatory network for specification and commitment of murine T cells

T cells develop from multipotent progenitors by a gradual process dependent on intrathymic Notch signaling and coupled with extensive proliferation. The stages leading them to T-cell lineage commitment are well characterized by single-cell and bulk RNA analyses of sorted populations and by direct measurements of precursor-product relationships. This process depends not only on Notch signaling but also on multiple transcription factors, some associated with stemness and multipotency, some with alternative lineages, and others associated with T-cell fate. These factors interact in opposing or semi-independent T cell gene regulatory network (GRN) subcircuits that are increasingly well defined. A newly comprehensive picture of this network has emerged. Importantly, because key factors in the GRN can bind to markedly different genomic sites at one stage than they do at other stages, the genes they significantly regulate are also stage-specific. Global transcriptome analyses of perturbations have revealed an underlying modular structure to the T-cell commitment GRN, separating decisions to lose "stem-ness" from decisions to block alternative fates. Finally, the updated network sheds light on the intimate relationship between the T-cell program, which depends on the thymus, and the innate lymphoid cell (ILC) program, which does not.

Dose-dependent effect of GFI1 expression in the reconstitution and the differentiation capacity of HSCs

GFI1 is a transcriptional repressor and plays a pivotal role in regulating the differentiation of hematopoietic stem cells (HSCs) towards myeloid and lymphoid cells. Serial transplantation of Gfi1 deficient HSCs repopulated whole hematopoietic system but in a competitive setting involving wild-type HSCs, they lose this ability. The underlying mechanisms to this end are poorly understood. To better understand this, we used different mouse strains that express either loss of both Gfi1 alleles (Gfi1-KO), with reduced expression of GFI1 (GFI1-KD) or wild-type Gfi1/GFI1 (Gfi1-/GFI1-WT; corresponding to the mouse and human alleles). We observed that loss of Gfi1 or reduced expression of GFI1 led to a two to four fold lower number of HSCs (defined as Lin^-Sca1⁺c-Kit⁺CD150⁺CD48^-) compared to GFI1-WT mice. To study the functional influence of different levels of GFI1 expression on HSCs function, HSCs from Gfi1-WT (expressing CD45.1 + surface antigens) and HSCs from GFI1-KD or -KO (expressing CD45.2 + surface antigens) mice were sorted and co-transplanted into lethally irradiated host mice. Every 4 weeks, CD45.1+ and CD45.2 + on different lineage mature cells were analyzed by flow cytometry. At least 16 weeks later, mice were sacrificed, and the percentage of HSCs and progenitors including GMPs, CMPs and MEPs in the total bone marrow cells was calculated as well as their CD45.1 and CD45.2 expression. In the case of co-transplantation of GFI1-KD with Gfi1-WT HSCs, the majority of HSCs (81% ± 6%) as well as the majority of mature cells (88% ± 10%) originated from CD45.2 + GFI1-KD HSCs. In the case of co-transplantation of Gfi1-KO HSCs with Gfi1-WT HSCs, the majority of HSCs originated from CD45.2+ and therefore from Gfi1-KO (61% ± 20%); however, only a small fraction of progenitors and mature cells originated from Gfi1-KO HSCs (<1%). We therefore in summary propose that GFI1 has a dose-dependent role in the self-renewal and differentiation of HSCs.

Severe Inflammatory Reactions in Mice Expressing a GFI1P2A Mutant Defective in Binding to the Histone Demethylase KDM1A (LSD1)

GFI1 is a DNA-binding transcription factor that regulates hematopoiesis by repressing target genes through its association with complexes containing histone demethylases such as KDM1A (LSD1) and histone deacetylases (HDACs). To study the consequences of the disruption of the complex between GFI1 and histone-modifying enzymes, we have used knock-in mice harboring a P2A mutation in GFI1 coding region that renders it unable to bind LSD1 and associated histone-modifying enzymes such as HDACs. GFI1^P2A mice die prematurely and show increased numbers of memory effector and regulatory T cells in the spleen accompanied by a severe systemic inflammation with high serum levels of IL-6, TNF-α, and IL-1β and overexpression of the gene encoding the cytokine oncostatin M (OSM). We identified lung alveolar macrophages, CD8 T cell from the spleen and thymic eosinophils, and monocytes as the sources of these cytokines in GFI1^P2A mice. Chromatin immunoprecipitation showed that GFI1/LSD1 complexes occupy sites at the Osm promoter and an intragenic region of the Tnfα gene and that a GFI1^P2A mutant still remains bound at these sites even without LSD1. Methylation and acetylation of histone H3 at these sites were enriched in cells from GFI1^P2A mice, the H3K27 acetylation being the most significant. These data suggest that the histone modification facilitated by GFI1 is critical to control inflammatory pathways in different cell types, including monocytes and eosinophils, and that a disruption of GFI1-associated complexes can lead to systemic inflammation with fatal consequences.

The transcription factors GFI1 and GFI1B as modulators of the innate and acquired immune response

GFI1 and GFI1B are small nuclear proteins of 45 and 37kDa, respectively, that have a simple two-domain structure: The first consists of a group of six c-terminal C₂H₂ zinc finger motifs that are almost identical in sequence and bind to very similar, specific DNA sites. The second is an N-terminal 20 amino acid SNAG domain that can bind to the pocket of the histone demethylase KDM1A (LSD1) near its active site. When bound to DNA, both proteins act as bridging factors that bring LSD1 and associated proteins into the vicinity of methylated substrates, in particular histone H3 or TP53. GFI1 can also bring methyl transferases such as PRMT1 together with its substrates that include the DNA repair proteins MRE11 and 53BP1, thereby enabling their methylation and activation. While GFI1B is expressed almost exclusively in the erythroid and megakaryocytic lineage, GFI1 has clear biological roles in the development and differentiation of lymphoid and myeloid immune cells. GFI1 is required for lymphoid/myeloid and monocyte/granulocyte lineage decision as well as the correct nuclear interpretation of a number of important immune-signaling pathways that are initiated by NOTCH1, interleukins such as IL2, IL4, IL5 or IL7, by the pre TCR or -BCR receptors during early lymphoid differentiation or by T and B cell receptors during activation of lymphoid cells. Myeloid cells also depend on GFI1 at both stages of early differentiation as well as later stages in the process of activation of macrophages through Toll-like receptors in response to pathogen-associated molecular patterns. The knowledge gathered on these factors over the last decades puts GFI1 and GFI1B at the center of many biological processes that are critical for both the innate and acquired immune system.

How transcription factors drive choice of the T cell fate

Recent evidence has elucidated how multipotent blood progenitors transform their identities in the thymus and undergo commitment to become T cells. Together with environmental signals, a core group of transcription factors have essential roles in this process by directly activating and repressing specific genes. Many of these transcription factors also function in later T cell development, but control different genes. Here, we review how these transcription factors work to change the activities of specific genomic loci during early intrathymic development to establish T cell lineage identity. We introduce the key regulators and highlight newly emergent insights into the rules that govern their actions. Whole-genome deep sequencing-based analysis has revealed unexpectedly rich relationships between inherited epigenetic states, transcription factor-DNA binding affinity thresholds and influences of given transcription factors on the activities of other factors in the same cells. Together, these mechanisms determine T cell identity and make the lineage choice irreversible.

Multifaceted Actions of GFI1 and GFI1B in Hematopoietic Stem Cell Self-Renewal and Lineage Commitment

Growth factor independence 1 (GFI1) and the closely related protein GFI1B are small nuclear proteins that act as DNA binding transcriptional repressors. Both recognize the same consensus DNA binding motif via their C-terminal zinc finger domains and regulate the expression of their target genes by recruiting chromatin modifiers such as histone deacetylases (HDACs) and demethylases (LSD1) by using an N-terminal SNAG domain that comprises only 20 amino acids. The only region that is different between both proteins is the region that separates the zinc finger domains and the SNAG domain. Both proteins are co-expressed in hematopoietic stem cells (HSCs) and, to some extent, in multipotent progenitors (MPPs), but expression is specified as soon as early progenitors and show signs of lineage bias. While expression of GFI1 is maintained in lymphoid primed multipotent progenitors (LMPPs) that have the potential to differentiate into both myeloid and lymphoid cells, GFI1B expression is no longer detectable in these cells. By contrast, GFI1 expression is lost in megakaryocyte precursors (MKPs) and in megakaryocyte-erythrocyte progenitors (MEPs), which maintain a high level of GFI1B expression. Consequently, GFI1 drives myeloid and lymphoid differentiation and GFI1B drives the development of megakaryocytes, platelets, and erythrocytes. How such complementary cell type- and lineage-specific functions of GFI1 and GFI1B are maintained is still an unresolved question in particular since they share an almost identical structure and very similar biochemical modes of actions. The cell type-specific accessibility of GFI1/1B binding sites may explain the fact that very similar transcription factors can be responsible for very different transcriptional programming. An additional explanation comes from recent data showing that both proteins may have additional non-transcriptional functions. GFI1 interacts with a number of proteins involved in DNA repair and lack of GFI1 renders HSCs highly susceptible to DNA damage-induced death and restricts their proliferation. In contrast, GFI1B binds to proteins of the beta-catenin/Wnt signaling pathway and lack of GFI1B leads to an expansion of HSCs and MKPs, illustrating the different impact that GFI1 or GFI1B has on HSCs. In addition, GFI1 and GFI1B are required for endothelial cells to become the first blood cells during early murine development and are among those transcription factors needed to convert adult endothelial cells or fibroblasts into HSCs. This role of GFI1 and GFI1B bears high significance for the ongoing effort to generate hematopoietic stem and progenitor cells de novo for the autologous treatment of blood disorders such as leukemia and lymphoma.

Temporal Expression of Bim Limits the Development of Agonist-Selected Thymocytes and Skews Their TCRβ Repertoire

CD8αα TCRαβ⁺ intestinal intraepithelial lymphocytes play a critical role in promoting intestinal homeostasis, although mechanisms controlling their development and peripheral homeostasis remain unclear. In this study, we examined the spatiotemporal role of Bim in the thymic selection of CD8αα precursors and the fate of these cells in the periphery. We found that T cell-specific expression of Bim during early/cortical, but not late/medullary, thymic development controls the agonist selection of CD8αα precursors and limits their private TCRβ repertoire. During this process, agonist-selected double-positive cells lose CD4/8 coreceptor expression and masquerade as double-negative (DN) TCRαβ^hi thymocytes. Although these DN thymocytes fail to re-express coreceptors after OP9-DL1 culture, they eventually mature and accumulate in the spleen where TCR and IL-15/STAT5 signaling promotes their conversion to CD8αα cells and their expression of gut-homing receptors. Adoptive transfer of splenic DN cells gives rise to CD8αα cells in the gut, establishing their precursor relationship in vivo. Interestingly, Bim does not restrict the IL-15-driven maturation of CD8αα cells that is critical for intestinal homeostasis. Thus, we found a temporal and tissue-specific role for Bim in limiting thymic agonist selection of CD8αα precursors and their TCRβ repertoire, but not in the maintenance of CD8αα intraepithelial lymphocytes in the intestine.

Global DNA methylation patterns in Barrett's esophagus, dysplastic Barrett's, and esophageal adenocarcinoma are associated with BMI, gender, and tobacco use

BACKGROUND

The risk of developing Barrett's esophagus (BE) and/or esophageal adenocarcinoma (EAC) is associated with specific demographic and behavioral factors, including gender, obesity/elevated body mass index (BMI), and tobacco use. Alterations in DNA methylation, an epigenetic modification that can affect gene expression and that can be influenced by environmental factors, is frequently present in both BE and EAC and is believed to play a role in the formation of BE and its progression to EAC. It is currently unknown whether obesity or tobacco smoking influences the risk of developing BE/EAC via the induction of alterations in DNA methylation. To investigate this possibility, we assessed the genome-wide methylation status of 81 esophageal tissues, including BE, dysplastic BE, and EAC epithelia using HumanMethylation450 BeadChips (Illumina).

RESULTS

We found numerous differentially methylated loci in the esophagus tissues when comparing males to females, obese to lean individuals, and smokers to nonsmokers. Differences in DNA methylation between these groups were seen in a variety of functional genomic regions and both within and outside of CpG islands. Several cancer-related pathways were found to have differentially methylated genes between these comparison groups.

CONCLUSIONS

Our findings suggest obesity and tobacco smoking may influence DNA methylation in the esophagus and raise the possibility that these risk factors affect the development of BE, dysplastic BE, and EAC through influencing the epigenetic status of specific loci that have a biologically plausible role in cancer formation.

The ubiquitin ligase Huwe1 regulates the maintenance and lymphoid commitment of hematopoietic stem cells

Hematopoietic stem cells (HSCs) are dormant in the bone marrow and can be activated in response to diverse stresses to replenish all blood cell types. Here we identify the ubiquitin ligase Huwe1 as a crucial regulator of HSC functions via its post-translational control of N-myc. We found Huwe1 to be essential for HSC self-renewal, quiescence and lymphoid fate specification. Using a novel fluorescent fusion allele (Mycn^M), we observed that N-myc expression was restricted to the most immature, multipotent stem and progenitor populations. N-myc was upregulated in response to stress or upon loss of Huwe1, leading to increased proliferation and stem cell exhaustion. Mycn depletion reversed most of these phenotypes in vivo, suggesting that the attenuation of N-myc by Huwe1 is essential to reestablish homeostasis following stress.

GFI1 functions in transcriptional control and cell fate determination require SNAG domain methylation to recruit LSD1

Proper hematopoietic cell fate decisions require co-ordinated functions of transcription factors, their associated co-regulators, and histone-modifying enzymes. Growth factor independence 1 (GFI1) is a zinc finger transcriptional repressor and master regulator of normal and malignant hematopoiesis. While several GFI1-interacting proteins have been described, how GFI1 leverages these relationships to carry out transcriptional repression remains unclear. Here, we describe a functional axis involving GFI1, SMYD2, and LSD1 that is a critical contributor to GFI1-mediated transcriptional repression. SMYD2 methylates lysine-8 (K8) within a -(8)KSKK(11)- motif embedded in the GFI1 SNAG domain. Methylation-defective GFI1 SNAG domain lacks repressor function due to failure of LSD1 recruitment and persistence of promoter H3K4 di-methyl marks. Methylation-defective GFI1 also fails to complement GFI1 depletion phenotypes in developing zebrafish and lacks pro-growth and survival functions in lymphoid leukemia cells. Our data show a discrete methylation event in the GFI1 SNAG domain that facilitates recruitment of LSD1 to enable transcriptional repression and co-ordinate control of hematopoietic cell fate in both normal and malignant settings.

Forging T-Lymphocyte Identity: Intersecting Networks of Transcriptional Control

T-lymphocyte development branches off from other lymphoid developmental programs through its requirement for sustained environmental signals through the Notch pathway. In the thymus, Notch signaling induces a succession of T-lineage regulatory factors that collectively create the T-cell identity through distinct steps. This process involves both the staged activation of T-cell identity genes and the staged repression of progenitor-cell-inherited regulatory genes once their roles in self-renewal and population expansion are no longer needed. With the recent characterization of innate lymphoid cells (ILCs) that share transcriptional regulation programs extensively with T-cell subsets, T-cell identity can increasingly be seen as defined in modular terms, as the processes selecting and actuating effector function are potentially detachable from the processes generating and selecting clonally unique T-cell receptor structures. The developmental pathways of different classes of T cells and ILCs are distinguished by the numbers of prerequisites of gene rearrangement, selection, and antigen contact before the cells gain access to nearly common regulatory mechanisms for choosing effector function. Here, the major classes of transcription factors that interact with Notch signals during T-lineage specification are discussed in terms of their roles in these programs, the evidence for their spectra of target genes at different stages, and their cross-regulatory and cooperative actions with each other. Specific topics include Notch modulation of PU.1 and GATA-3, PU.1-Notch competition, the relationship between PU.1 and GATA-3, and the roles of E proteins, Bcl11b, and GATA-3 in guiding acquisition of T-cell identity while avoiding redirection to an ILC fate.

From cytopenia to leukemia: the role of Gfi1 and Gfi1b in blood formation

The DNA-binding zinc finger transcription factors Gfi1 and Gfi1b were discovered more than 20 years ago and are recognized today as major regulators of both early hematopoiesis and hematopoietic stem cells. Both proteins function as transcriptional repressors by recruiting histone-modifying enzymes to promoters and enhancers of target genes. The establishment of Gfi1 and Gfi1b reporter mice made it possible to visualize their cell type-specific expression and to understand their function in hematopoietic lineages. We now know that Gfi1 is primarily important in myeloid and lymphoid differentiation, whereas Gfi1b is crucial for the generation of red blood cells and platelets. Several rare hematologic diseases are associated with acquired or inheritable mutations in the GFI1 and GFI1B genes. Certain patients with severe congenital neutropenia carry mutations in the GFI1 gene that lead to the disruption of the C-terminal zinc finger domains. Other mutations have been found in the GFI1B gene in families with inherited bleeding disorders. In addition, the Gfi1 locus is frequently found to be a proviral integration site in retrovirus-induced lymphomagenesis, and new, emerging data suggest a role of Gfi1 in human leukemia and lymphoma, underlining the role of both factors not only in normal hematopoiesis, but also in a wide spectrum of human blood diseases.

Transcription factors and target genes of pre-TCR signaling

Almost 30 years ago pioneering work by the laboratories of Harald von Boehmer and Susumo Tonegawa provided the first indications that developing thymocytes could assemble a functional TCRβ chain-containing receptor complex, the pre-TCR, before TCRα expression. The discovery and study of the pre-TCR complex revealed paradigms of signaling pathways in control of cell survival and proliferation, and culminated in the recognition of the multifunctional nature of this receptor. As a receptor integrated in a dynamic developmental process, the pre-TCR must be viewed not only in the light of the biological outcomes it promotes, but also in context with those molecular processes that drive its expression in thymocytes. This review article focuses on transcription factors and target genes activated by the pre-TCR to drive its different outcomes.

The transcription factor GFI1 negatively regulates NLRP3 inflammasome activation in macrophages

Interleukin-1β (IL-1β) secretion downstream of Toll-like receptor (TLR) activation is tightly controlled at the transcriptional and post-translational levels. NLRP3 inflammasome is involved in the maturation of pro-IL-1β, with NLRP3 expression identified as the limiting factor for inflammasome activation. Previously, we had demonstrated that the zinc-finger protein GFI1 inhibits pro-IL-1β transcription. Here, we show that GFI1 inhibits NLRP3 inflammasome activation and IL-1β secretion in macrophages. GFI1 suppressed Nlrp3 transcription via two mechanisms: (1) by binding to the Gli-responsive element 1 (GRE1) in the Nlrp3 promoter; and (2) by antagonizing the nuclear factor-κB (NF-κB) transcriptional activity. Thus, GFI1 negatively regulates TLR-mediated IL-1β production at both transcriptional and post-translational levels.

Growth Factor Independence-1 (Gfi1) Is Required for Pancreatic Acinar Unit Formation and Centroacinar Cell Differentiation

BACKGROUND & AIMS

The genetic specification of the compartmentalized pancreatic acinar/centroacinar unit is poorly understood. Growth factor independence-1 (Gfi1) is a zinc finger transcriptional repressor that regulates hematopoietic stem cell maintenance, pre-T-cell differentiation, formation of granulocytes, inner ear hair cells, and the development of secretory cell types in the intestine. As GFI1/Gfi1 is expressed in human and rodent pancreas, we characterized the potential function of Gfi1 in mouse pancreatic development.

METHODS

Gfi1 knockout mice were analyzed at histological and molecular levels, including qRT-PCR, in situ hybridization, immunohistochemistry, and electron microscopy.

RESULTS

Loss of Gfi1 impacted formation and structure of the pancreatic acinar/centroacinar unit. Histologic and ultrastructural analysis of Gfi1-null pancreas revealed specific defects at the level of pancreatic acinar cells as well as the centroacinar cells (CACs) in Gfi1^-/- mice when compared with wild-type littermates. Pancreatic endocrine differentiation, islet architecture, and function were unaffected. Organ domain patterning and the formation of ductal cells occurred normally during the murine secondary transition (E13.5-E14.5) in the Gfi1^-/- pancreas. However, at later gestational time points (E18.5), expression of cellular markers for CACs was substantially reduced in Gfi1^-/- mice, corroborated by electron microscopy imaging of the acinar/centroacinar unit. The reduction in CACs was correlated with an exocrine organ defect. Postnatally, Gfi1 deficiency resulted in severe pancreatic acinar dysplasia, including loss of granulation, autolytic vacuolation, and a proliferative and apoptotic response.

CONCLUSIONS

Gfi1 plays an important role in regulating the development of pancreatic CACs and the function of pancreatic acinar cells.

SCL, LMO1 and Notch1 reprogram thymocytes into self-renewing cells

The molecular determinants that render specific populations of normal cells susceptible to oncogenic reprogramming into self-renewing cancer stem cells are poorly understood. Here, we exploit T-cell acute lymphoblastic leukemia (T-ALL) as a model to define the critical initiating events in this disease. First, thymocytes that are reprogrammed by the SCL and LMO1 oncogenic transcription factors into self-renewing pre-leukemic stem cells (pre-LSCs) remain non-malignant, as evidenced by their capacities to generate functional T cells. Second, we provide strong genetic evidence that SCL directly interacts with LMO1 to activate the transcription of a self-renewal program coordinated by LYL1. Moreover, LYL1 can substitute for SCL to reprogram thymocytes in concert with LMO1. In contrast, inhibition of E2A was not sufficient to substitute for SCL, indicating that thymocyte reprogramming requires transcription activation by SCL-LMO1. Third, only a specific subset of normal thymic cells, known as DN3 thymocytes, is susceptible to reprogramming. This is because physiological NOTCH1 signals are highest in DN3 cells compared to other thymocyte subsets. Consistent with this, overexpression of a ligand-independent hyperactive NOTCH1 allele in all immature thymocytes is sufficient to sensitize them to SCL-LMO1, thereby increasing the pool of self-renewing cells. Surprisingly, hyperactive NOTCH1 cannot reprogram thymocytes on its own, despite the fact that NOTCH1 is activated by gain of function mutations in more than 55% of T-ALL cases. Rather, elevating NOTCH1 triggers a parallel pathway involving Hes1 and Myc that dramatically enhances the activity of SCL-LMO1 We conclude that the acquisition of self-renewal and the genesis of pre-LSCs from thymocytes with a finite lifespan represent a critical first event in T-ALL. Finally, LYL1 and LMO1 or LMO2 are co-expressed in most human T-ALL samples, except the cortical T subtype. We therefore anticipate that the self-renewal network described here may be relevant to a majority of human T-ALL.

Deciphering the initiating events in lymphoid leukemia is important for the development of new therapeutic strategies. In this manuscript, we define oncogenic reprogramming as the process through which non-self-renewing progenitors are converted into pre-leukemic stem cells with sustained self-renewal capacities. We provide strong genetic evidence that this step is rate-limiting in leukemogenesis and requires the activation of a self-renewal program by oncogenic transcription factors, as exemplified by SCL and LMO1. Furthermore, NOTCH1 is a pathway that drives cell fate in the thymus. We demonstrate that homeostatic NOTCH1 levels that are highest in specific thymocyte subsets determine their susceptibilities to oncogenic reprogramming by SCL and LMO1. Our data provide novel insight into the acquisition of self-renewal as a critical first step in lymphoid cell transformation, requiring the synergistic interaction of oncogenic transcription factors with a cellular context controlled by high physiological NOTCH1.

Developmental gene networks: a triathlon on the course to T cell identity

Cells acquire their ultimate identities by activating combinations of transcription factors that initiate and sustain expression of the appropriate cell type-specific genes. T cell development depends on the progression of progenitor cells through three major phases, each of which is associated with distinct transcription factor ensembles that control the recruitment of these cells to the thymus, their proliferation, lineage commitment and responsiveness to T cell receptor signals, all before the allocation of cells to particular effector programmes. All three phases are essential for proper T cell development, as are the mechanisms that determine the boundaries between each phase. Cells that fail to shut off one set of regulators before the next gene network phase is activated are predisposed to leukaemic transformation.

Shared mechanisms between Drosophila peripheral nervous system development and human neurodegenerative diseases

Signaling pathways and cellular processes that regulate neural development are used post-developmentally for proper function and maintenance of the nervous system. Genes that have been studied in the context of the development of Drosophila peripheral nervous system (PNS) and neuromuscular junction (NMJ) have been identified as players in the pathogenesis of human neurodegenerative diseases, including spinocerebellar ataxia, amyotrophic lateral sclerosis, and spinal muscular atrophy. Hence, by unraveling the molecular mechanisms that underlie proneural induction, cell fate determination, axonal targeting, dendritic branching, and synapse formation in Drosophila, novel features related to these disorders have been revealed. In this review, we summarize and discuss how studies of Drosophila PNS and NMJ development have provided guidance in experimental approaches for these diseases.