Growth/differentiation factor 15 (GDF15), also known as MIC-1, is a distant member of the transforming growth factor-β (TGF-β) superfamily and has been implicated in various biological functions, including cancer cachexia, renal and heart failure, atherosclerosis and metabolism. A connection between GDF15 and body-weight regulation was initially suggested on the basis of an observation that increasing GDF15 levels in serum correlated with weight loss in individuals with advanced prostate cancer. In animal models, overexpression of GDF15 leads to a lean phenotype, hypophagia and other improvements in metabolic parameters, suggesting that recombinant GDF15 protein could potentially be used in the treatment of obesity and type 2 diabetes. However, the signaling and mechanism of action of GDF15 are poorly understood owing to the absence of a clearly identified cognate receptor. Here we report that GDNF-family receptor α-like (GFRAL), an orphan member of the GFR-α family, is a high-affinity receptor for GDF15. GFRAL binds to GDF15 in vitro and is required for the metabolic actions of GDF15 with respect to body weight and food intake in vivo in mice. Gfral mice were refractory to the effects of recombinant human GDF15 on body-weight, food-intake and glucose parameters. Blocking the interaction between GDF15 and GFRAL with a monoclonal antibody prevented the metabolic effects of GDF15 in rats. Gfral mRNA is highly expressed in the area postrema of mouse, rat and monkey, in accordance with previous reports implicating this region of the brain in the metabolic actions of GDF15 (refs. 4,5,6). Together, our data demonstrate that GFRAL is a receptor for GDF15 that mediates the metabolic effects of GDF15.

Differential gene expression, with its precise start and stop times, is believed to be critical for the programmed development of new cells and tissues. Within the developing fetus, one tissue of particular interest is fetal liver. This organ undergoes rapid changes in the pathway toward liver development in utero since it is also the major site of hematopoiesis, until bone marrow hematopoiesis predominates. Believing that patterns would emerge from the bi-weekly large-scale inspection of expressed genes in the fetal liver, we employed differential display reverse transcription-polymerase chain reaction (DDRT-PCR) as ourprimary inspection tool. Using DDRT-PCR, we isolated cDNAs differentially expressed throughout fetal liver development and in adult liver. We displayed approximately 25 000 cDNAs from 10 and 24 week fetal liver and adult liver. From this initial screen, we determined that approximately 0.1-1% of the mRNA population undergoes expression changes. We extracted, purified and sequenced 25 differentially displayed cDNA bands. Fourteen cDNAs had similarities to known genes, while 11 cDNAs were not similar to any characterized gene. The differentially expressed cDNAs from known genes present in fetal liver include alpha-fetoprotein, stem cell factor, erythroid alpha-spectrin, 2,3-bisphosphoglycerate mutase, insulin-like growth factor-2, porphobilinogen deaminase and Mac30. The differentially expressed cDNAs present in adult liver but not in 10 week fetal liver were nicotinamide deaminase, human fibrinogen-related protein and alpha-acid glycoprotein. The majority of differentially expressed genes found during this effort appear to be turned on during organogenesis, however, some genes were found that are apparently turned off completely.

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Differential display of mRNA is a simple, sensitive and powerful method to identify differentially expressed gene fragments. The main drawback of differential display is the lack of reproducibility and the inability to read and compare complex gels. This issue results from employing unoptimized primer combinations and non-specific amplification, most likely due to unavoidable low annealing temperatures. In order to display most of the expressed transcripts (80-120 bands/lane), 26 different 5' primers were used in conjunction with nine different 3' poly (dT) primers. These primer combinations, used with the optimized annealing temperature for each set of primers, produced highly reproducible bands. BSA has a direct effect on the number of bands resolved. Variations in ramping time (9-40 s) had little or no effect on the resolution and reproducibility of differential display.