Upregulated TNF/Eiger signaling mediates stem cell recovery and tissue homeostasis during nutrient resupply in Drosophila testis

Drosophila TNF/TNFRs: At the crossroad between metabolism, immunity, and tissue homeostasis

Tumor necrosis factor (TNF)-α is a highly conserved proinflammatory cytokine with important functions in immunity, tissue repair, and cellular homeostasis. Due to the simplicity of the Drosophila TNF-TNF receptor (TNFR) system and a broad genetic toolbox, the fly has played a pivotal role in deciphering the mechanisms underlying TNF-mediated physiological and pathological functions. In this review, we summarize the recent advances in our understanding of how local and systemic sources of Egr/TNF contribute to its antitumor and tumor-promoting properties, and its emerging functions in adaptive growth responses, sleep regulation, and adult tissue homeostasis. The recent annotation of TNF as an adipokine and its indisputable contribution to obesity- and cancer-associated metabolic diseases have provoked a new area of research focusing on its dual function in regulating immunity and energy homeostasis. Here, we discuss the role of TNFR signaling in coupling immune and metabolic processes and how this might be relevant in the adaption of host to environmental stresses, or, in the case of obesity, promote metabolic derangements and disease.

Escargot controls somatic stem cell maintenance through the attenuation of the insulin receptor pathway in Drosophila

Adult stem cells coordinate intrinsic and extrinsic, local and systemic, cues to maintain the proper balance between self-renewal and differentiation. However, the precise mechanisms stem cells use to integrate these signals remain elusive. Here, we show that Escargot (Esg), a member of the Snail family of transcription factors, regulates the maintenance of somatic cyst stem cells (CySCs) in the Drosophila testis by attenuating the activity of the pro-differentiation insulin receptor (InR) pathway. Esg positively regulates the expression of an antagonist of insulin signaling, ImpL2, while also attenuating the expression of InR. Furthermore, Esg-mediated repression of the InR pathway is required to suppress CySC loss in response to starvation. Given the conservation of Snail-family transcription factors, characterizing the mechanisms by which Esg regulates cell-fate decisions during homeostasis and a decline in nutrient availability is likely to provide insight into the metabolic regulation of stem cell behavior in other tissues and organisms.

The Emerging Roles of JNK Signaling in Drosophila Stem Cell Homeostasis

The Jun N-terminal kinase (JNK) pathway is an evolutionary conserved kinase cascade best known for its roles during stress-induced apoptosis and tumor progression. Recent findings, however, have identified new roles for this pleiotropic pathway in stem cells during regenerative responses and in cellular plasticity. Here, we provide an overview of recent findings about the new roles of JNK signaling in stem cell biology using two well-established Drosophila models: the testis and the intestine. We highlight the pathway’s roles in processes such as proliferation, death, self-renewal and reprogramming, and discuss the known parallels between flies and mammals.