Sex differences in schizophrenia are well known, but their genetic basis has not been identified. We performed a genome-wide association scan for schizophrenia in an Ashkenazi Jewish population using DNA pooling. We found a female-specific association with rs7341475, a SNP in the fourth intron of the reelin (RELN) gene (p = 2.9 × 10−5 in women), with a significant gene-sex effect (p = 1.8 × 10−4). We studied rs7341475 in four additional populations, totaling 2,274 cases and 4,401 controls. A significant effect was observed only in women, replicating the initial result (p = 2.1 × 10−3 in women; p = 4.2 × 10−3 for gene-sex interaction). Based on all populations the estimated relative risk of women carrying the common genotype is 1.58 (p = 8.8 × 10−7; p = 1.6 × 10−5 for gene-sex interaction). The female-specific association between RELN and schizophrenia is one of the few examples of a replicated sex-specific genetic association in any disease.

The nonobese diabetic (NOD) mouse spontaneously develops autoimmune‐mediated diseases such as diabetes and Sjögren′s syndrome. To investigate whether NOD genes also promote autoimmune‐mediatedarthritis we established a NOD strain with an MHC class II fragment containing the Aq class II gene predisposing for collagen induced arthritis (NOD.Q). However, this mouse was resistant to arthritis in contrast to other Aq expressing strains such as B10.Q and DBA/1. To determine the major resistance factor/s, a genetic analysis was performed. (NOD.Q×B10.Q)F1 mice were resistant, whereas 27% of the (NOD.Q×B10.Q)F2 mice developed severe arthritis. Genetic mapping of 353 F2 mice revealed two loci associated with arthritis. One locus was found on chromosome 2 (LOD score 9.8), at the location of the complement factor 5 (C5) gene. The susceptibility allele was from B10.Q, which contains a productive C5 encoding gene in contrast to NOD.Q. The other significant locus was found on chromosome 1 (LOD score 5.6) close to the Fc‐gamma receptor IIb gene, where NOD carried the susceptible allele. An interaction between the two loci was observed, indicating that they operate on the same or on interacting pathways. The genetic control of arthritis is unique in comparison to diabetes, since none of these loci have been identified in analysis of diabetes susceptibility.

Fibroblast growth factor (FGF) signaling controls axis formation during endoderm development. Studies in lower vertebrates have demonstrated that FGF2 primarily patterns the ventral foregut endoderm into liver and lung, whereas FGF4 exhibits broad anterior-posterior and leftright patterning activities. Furthermore, an inductive role of FGF2 during dorsal pancreas formation has been shown. However, whether FGF2 plays a similar role during human endoderm development remains unknown. Here, we show that FGF2 specifies hESC-derived definitive endoderm (DE) into different foregut lineages in a dosage-dependent manner. Specifically, increasing concentrations of FGF2 inhibits hepatocyte differentiation, whereas intermediate concentration of FGF2 promotes differentiation toward a pancreatic cell fate. At high FGF2 levels specification of midgut endoderm into small intestinal progenitors is increased at the expense of PDX1 1 pancreatic progenitors. High FGF2 concentrations also promote differentiation toward an anterior foregut pulmonary cell fate. Finally, by dissecting the FGF receptor intracellular pathway that regulates pancreas specification, we demonstrate for the first time to the best of our knowledge that induction of PDX1 1 pancreatic progenitors relies on FGF2-mediated activation of the MAPK signaling pathway. Altogether, these observations suggest a broader gut endodermal patterning activity of FGF2 that corresponds to what has previously been advocated for FGF4, implying a functional switch from FGF4 to FGF2 during evolution. Thus, our results provide new knowledge of how cell fate specification of human DE is controlledfacts that will be of great value for future regenerative cell therapies. STEM CELLS 2010;28:45-56 Disclosure of potential conflicts of interest is found at the end of this article.

BackgroundRetinoic acid (RA) and fibroblast growth factor 4 (FGF4) signaling control endoderm patterning and pancreas induction/expansion. Based on these findings, RA and FGFs, excluding FGF4, have frequently been used in differentiation protocols to direct differentiation of hESCs into endodermal and pancreatic cell types. In vivo, these signaling pathways act in a temporal and concentration-dependent manner. However, in vitro, the underlying basis for the time of addition of growth and differentiation factors (GDFs), including RA and FGFs, as well as the concentration is lacking. Thus, in order to develop robust and reliable differentiation protocols of ESCs into mature pancreatic cell types, including insulin-producing β cells, it will be important to mechanistically understand each specification step. This includes differentiation of mesendoderm/definitive endoderm into foregut endoderm- the origin of pancreatic endoderm.Methodology/Principal FindingsHere, we provide data on the individual and combinatorial role of RA and FGF4 in directing differentiation of ActivinA (AA)-induced hESCs into PDX1-expressing cells. FGF4's ability to affect endoderm patterning and specification in vitro has so far not been tested. By testing out the optimal concentration and timing of addition of FGF4 and RA, we present a robust differentiation protocol that on average generates 32% PDX1+ cells. Furthermore, we show that RA is required for converting AA-induced hESCs into PDX1+ cells, and that part of the underlying mechanism involves FGF receptor signaling. Finally, further characterization of the PDX1+ cells suggests that they represent foregut endoderm not yet committed to pancreatic, posterior stomach, or duodenal endoderm.Conclusion/SignificanceIn conclusion, we show that RA and FGF4 jointly direct differentiation of PDX1+ foregut endoderm in a robust and efficient manner. RA signaling mediated by the early induction of RARβ through AA/Wnt3a is required for PDX1 expression. Part of RA's activity is mediated by FGF signaling.