During suboptimal growth conditions, Caenorhabditis elegans larvae undergo a global developmental arrest called “dauer.” During this stage, the germline stem cells (GSCs) become quiescent in an AMP-activated Protein Kinase (AMPK)-dependent manner, and in the absence of AMPK, the GSCs overproliferate and lose their reproductive capacity, leading to sterility when mutant animals resume normal growth. These defects correlate with the altered abundance and distribution of a number of chromatin modifications, all of which can be corrected by disabling components of the endogenous small RNA pathway, suggesting that AMPK regulates germ cell integrity by targeting an RNA interference (RNAi)-like pathway during dauer. The expression of AMPK in somatic cells restores all the germline defects, potentially through the transmission of small RNAs. Our findings place AMPK at a pivotal position linking energy stress detected in the soma to a consequent endogenous small RNA–mediated adaptation in germline gene expression, thereby challenging the “permeability" of the Weismann barrier.

During periods of energetic stress, Caenorhabditis elegans can execute a developmentally quiescent stage called “dauer”, during which all germline stem cells undergo a G2 cell cycle arrest. In animals that lack AMP-activated protein kinase (AMPK) signalling, the germ cells fail to arrest, undergo uncontrolled proliferation, and lose their reproductive capacity upon recovery from this quiescent stage. These germline defects are accompanied by, and likely result from, an altered chromatin landscape and gene expression program. Through genetic analysis we identified an allele of tbc-7, a predicted RabGAP protein that functions in the neurons, which when compromised, suppresses the germline hyperplasia in the dauer larvae, as well as the post-dauer sterility and somatic defects characteristic of AMPK mutants. This mutation also corrects the abundance and aberrant distribution of transcriptionally activating and repressive chromatin marks in animals that otherwise lack all AMPK signalling. We identified RAB-7 as one of the potential RAB proteins that is modulated by tbc-7 and show that the activity of RAB-7 is critical for the maintenance of germ cell integrity during the dauer stage. We reveal that TBC-7 is regulated by AMPK through two mechanisms when the animals enter the dauer stage. Acutely, the AMPK-mediated phosphorylation of TBC-7 reduces its activity, potentially by autoinhibition, thereby preventing the inactivation of RAB-7. In the more long term, AMPK regulates the miRNAs mir-1 and mir-44 to attenuate tbc-7 expression. Consistent with this, animals lacking mir-1 and mir-44 are post-dauer sterile, phenocopying the germline defects of AMPK mutants. Altogether, we have uncovered an AMPK-dependent and microRNA-regulated cellular trafficking pathway that is initiated in the neurons, and is critical to control germline gene expression cell non-autonomously in response to adverse environmental conditions.

BackgroundCaenorhabditis elegans can endure long periods of environmental stress by altering their development to execute a quiescent state called “dauer”. Previous work has implicated LKB1 - the causative gene in the autosomal dominant, cancer pre-disposing disease called Peutz-Jeghers Syndrome (PJS), and its downstream target AMPK, in the establishment of germline stem cell (GSC) quiescence during the dauer stage. Loss of function mutations in both LKB1/par-4 and AMPK/aak(0) result in untimely GSC proliferation during the onset of the dauer stage, although the molecular mechanism through which these factors regulate quiescence remains unclear. Curiously, the hyperplasia observed in par-4 mutants is more severe than AMPK-compromised dauer larvae, suggesting that par-4 has alternative downstream targets in addition to AMPK to regulate germline quiescence.ResultsWe conducted three genome-wide RNAi screens to identify potential downstream targets of the protein kinases PAR-4 and AMPK that mediate dauer-dependent GSC quiescence. First, we screened to identify genes that phenocopy the par-4-dependent hyperplasia when compromised by RNAi. Two additional RNAi screens were performed to identify genes that suppressed the germline hyperplasia in par-4 and aak(0) dauer larvae, respectively. Interestingly, a subset of the candidates we identified are involved in the regulation of cell polarity and cytoskeletal function downstream of par-4, in an AMPK-independent manner. Moreover, we show that par-4 temporally regulates actin cytoskeletal organization within the dauer germ line at the rachis-adjacent membrane, in an AMPK-independent manner.ConclusionOur data suggest that the regulation of the cytoskeleton and cell polarity may contribute significantly to the tumour suppressor function of LKB1/par-4.Electronic supplementary materialThe online version of this article (10.1186/s12864-018-4847-y) contains supplementary material, which is available to authorized users.

Sortilin (SORT1), or neurotensin receptor-3, is a scavenging receptor in the Vacuolar Protein Sorting 10 protein (Vps10p) family. SORT1 is involved in the internalization and trafficking of its ligands through an endocytic process and is associated with cancer cell survival and progression, making SORT1 a candidate for novel drug delivery. We recently reported on the pattern and prevalence of SORT1 expression in endometrial, breast, ovarian, colorectal, pancreas cancers, and skin melanoma. To better understand SORT1 expression, we screened tissues from different cancer types using the same immunohistochemistry (IHC) method. A total of 19 cancer tissue microarrays (TMAs) with 1394 evaluable cancer cores were screened. Each cancer core was scored using an H-score ranging from 0 to 300, where 0 corresponds to no cell stained for SORT1, while 300 corresponds to strong SORT1 staining in all cells. The table below summarizes the % of cores with moderate to high SORT1 expression (defined as H-score ≥100) as well as the average H-Score for each cancer type evaluated. Sub-analyses of SORT1 expression by tumor histological sub-type, stage and grade are also being performed. A total of 234 healthy or normal adjacent tissues cores were also assessed. Weak or null staining was observed in these tissues. Moderate staining was observed in specific cell types in kidney tubules and glomeruli, colonic mucosa, splenic sinusoidal spaces in red pulp, blood vessels in smooth muscle of spleen and colon, dendritic and axonal extensions of pyramidal-type neurons in brain, and testicular seminiferous tubules. SORT1 is currently being studied as a cancer target in a first-in-human (FIH) study of a peptide-drug conjugate (clinicaltrial.gov: NCT04706962). These results suggest that SORT1 is highly expressed in multiple tumors and is a promising target for the delivery and internalization of cancer therapeutic agents. Table 1. Cancer Type No. evaluable cores % of indication with H-score ≥ 100 Average H-Score Endometrial 94 90 197 Thyroid 108 92 188 Melanoma 155 83 184 Lung 152 58 112 SCLC 44 95 183 NSCLC 108 43 82 Bladder 118 81 156 Testis 40 100 116 Small intestine 54 63 102 Eye 26 46 83 Cervix 376 38 75 Prostate 150 39 71 Liver 121 23 52 Citation Format: Guylaine Roy, Pratik Kadekar, Lynn Marie Douglas, Maude Frappier, Jean-Christophe Currie, Jess Dhillon, Gregory Cesarone, Richard Siderits, Karen Kirchner, Michel Demeule, Christian Marsolais. Differential expression of a novel transport receptor, SORT1 (sortilin), in cancer versus healthy tissues that can be utilized for targeted delivery of anti-cancer drugs. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3942.

13C. elegans larvae can undergo a global developmental arrest following the execution of a diapause-14 like state called 'dauer' in response to unfavourable growth conditions. Survival in this stage 15 surpasses the normal lifespan of reproductive animals quite dramatically, and without any apparent 16 negative impact on their reproductive fitness. During this period, the germ cells become quiescent 17 and must retain their reproductive integrity so the animal can reproduce following recovery. This 18 germline stem cell (GSC) arrest requires the activity of AMP-activated protein kinase (AMPK) 19 and in its absence the germ line undergoes hyperplasia. We show here that AMPK mutant animals 20 exhibit complete sterility after recovery from dauer, suggesting that germ cell integrity is 21 compromised during this stage in the absence of AMPK. These defects correlate with altered 22 soma communicates with the germ line to establish the appropriate epigenetic modifications 36 required to adapt to acute environmental challenges. 37