Although members of the fibroblast growth factor (FGF) family and their receptors have well-established roles in embryogenesis, their contributions to adult physiology remain relatively unexplored. Here, we use real-time quantitative PCR to determine the mRNA expression patterns of all 22 FGFs, the seven principal FGF receptors (FGFRs), and the three members of the Klotho family of coreceptors in 39 different mouse tissues. Unsupervised hierarchical cluster analysis of the mRNA expression data reveals that most FGFs and FGFRs fall into two groups the expression of which is enriched in either the central nervous system or reproductive and gastrointestinal tissues. Interestingly, the FGFs that can act as endocrine hormones, including FGF15/19, FGF21, and FGF23, cluster in a third group that does not include any FGFRs, underscoring their roles in signaling between tissues. We further show that the most recently identified Klotho family member, Lactase-like, is highly and selectively expressed in brown adipose tissue and eye and can function as an additional coreceptor for FGF19. This FGF atlas provides an important resource for guiding future studies to elucidate the physiological functions of FGFs in adult animals.

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Mitochondria are complex organelles with a highly dynamic distribution and internal organization. Here, we demonstrate that mitofilin, a previously identified mitochondrial protein of unknown function, controls mitochondrial cristae morphology. Mitofilin is enriched in the narrow space between the inner boundary and the outer membranes, where it forms a homotypic interaction and assembles into a large multimeric protein complex. Down-regulation of mitofilin in HeLa cells by using specific small interfering RNA lead to decreased cellular proliferation and increased apoptosis, suggesting abnormal mitochondrial function. Although gross mitochondrial fission and fusion seemed normal, ultrastructural studies revealed disorganized mitochondrial inner membrane. Inner membranes failed to form tubular or vesicular cristae and showed as closely packed stacks of membrane sheets that fused intermittently, resulting in a complex maze of membranous network. Electron microscopic tomography estimated a substantial increase in inner:outer membrane ratio, whereas no cristae junctions were detected. In addition, mitochondria subsequently exhibited increased reactive oxygen species production and membrane potential. Although metabolic flux increased due to mitofilin deficiency, mitochondrial oxidative phosphorylation was not increased accordingly. We propose that mitofilin is a critical organizer of the mitochondrial cristae morphology and thus indispensable for normal mitochondrial function. INTRODUCTIONMitochondria are the center of cellular energy production and essential metabolic reactions. As double membranebound organelles, mitochondria from different species, tissues, and metabolic states are highly polymorphic in nature yet exhibit common structural features. The ultrastructural variations in mitochondrial architecture occur mainly due to the differences in the amount and shape of cristae, which derive from the infolded inner membrane in which protein complexes of oxidative phosphorylation and intermediate metabolism are embedded. Abundant cristae are found in mitochondria from tissues where energy demand is high. For example, mitochondria with densely packed cristae are observed in the flight muscle of the dragonfly, whereas the liver of a winter-starved frog displays mitochondria with sparse cristae (Ghadially, 1997). Furthermore, the inner membranes of isolated mitochondria undergo characteristic morphological changes in response to the metabolic state (Hackenbrock, 1966). Although little is known about the molecular mechanisms regulating cristae biogenesis and architecture, recent studies have implicated proteins resident in both the outer and inner membrane to have roles in this process.The mitochondrial fission and fusion machinery plays an essential role in the dynamics, division, distribution, and morphology of the organelle (Yaffe, 1999;Jensen et al., 2000;Griparic and van der Bliek, 2001;Shaw and Nunnari, 2002). Three evolutionarily conserved large GTPases, Dnm1/ Drp1/Dlp1, Fzo1/mitofusin, and Mgm1/MspI/OPA1, are...

SummaryCell type-specific genetic modification using the Cre/loxP system is a powerful tool for genetic analysis of distinct cell lineages. Because of the exquisite specificity of Vasa expression (confined to the germ cell lineage in invertebrate and vertebrate species), we hypothesized that a Vasa promoterdriven transgenic Cre line would prove useful for the germ cell lineage-specific inactivation of genes. Here we describe a transgenic mouse line, Vasa-Cre, where Cre is efficiently and specifically expressed in germ cells. Northern analysis showed that transgene expression was confined to the gonads. Cre-mediated recombination with the Rosa26-lacZ reporter was observed beginning at ~e15, and was >95% efficient in male and female germ cells by birth. There was no ectopic activity in most adults, although some animals showed more widespread lacZ expression. This Vasa-Cre transgenic line should thus prove useful for genetic analysis of diverse aspects of germ cell function and gametogenesis. KeywordsCre; vasa; germ cells; gonad Genetic approaches are well-suited for studies of gametogenesis and reproduction, processes that require complex interactions between germline and somatic cells, and hence are difficult to fully recapitulate in vitro. More recently, conditional gene targeting using the Cre/loxP system has emerged as an especially powerful method in reproductive genetics, particularly in the study of genes whose systemic inactivation is lethal. Critical to the success this approach is the availability of suitable Cre transgenes expressed in a wide range of distinct cell lineages at appropriate developmental timepoints (Kwan, 2002;Lewandoski, 2001). Previous germ cell Cre lines include ZP3-Cre, which is not active in primordial follicles but becomes induced following follicle growth; this line is thus useful for analyses of follicle growth or maternal contributions to the embryo (de Vries et al., 2000). A Cre knock-in into the TNAP (tissue nonspecific alkaline phosphatase) is active in primordial germ cells starting as early as e9.5. but the TNAP promoter is also active in other tissues (e.g. placenta and liver, among others) and such widespread expression may complicate interpretation of experiments where germ cellspecific gene inactivation is desired or required (if e.g. the locus is essential) (Lomeli et al., 2000).Vasa expression is confined to the germ cell lineage in species including Drosophila, zebrafish, mouse, and humans (Castrillon et al., 2000;Lasko and Ashburner, 1988 (Tanaka et al., 2000). We reasoned that a Vasa-Cre line could prove useful for studies of germ cell function following gonadal colonization, including many aspects of spermatogenesis and oogenesis, such as the assembly, activation, and growth of primordial follicles.We cloned a 5.6 kb DNA fragment containing mouse Vasa 5' regulatory sequences, including the transcriptional start site. This fragment contains canonical promoter sequences including a TATA box at −27 and more distant control elements important for germ cell specific ex...

In mammals, oocytes are packaged into compact structures-primordial follicles-which remain inert for prolonged intervals until individual follicles resume growth via a process known as primordial follicle activation. Here we show that the phosphoinositide 3-kinase (PI3K) signalling pathway controls primordial follicle activation through the forkhead transcription factor Foxo3. Within oocytes, Foxo3 is regulated by nucleocytoplasmic shuttling. Foxo3 is imported into the nucleus during primordial follicle assembly, and is exported upon activation. Oocyte-specific ablation of Pten resulted in PI3K-induced Akt activation, Foxo3 hyperphosphorylation, and Foxo3 nuclear export, thereby triggering primordial follicle activation, defining the steps by which the PI3K pathway and Foxo3 control this process. Inducible ablation of Pten and Foxo3 in adult oocytes using a new tool for genetic analysis of the germline, Vasa-Cre(ERT2), showed that this pathway functions throughout life. Thus, a principal physiologic role of the PI3K pathway is to control primordial follicle activation via Foxo3.