Research resource: Comprehensive expression atlas of the fibroblast growth factor system in adult mouse

Abstract

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.

Figure 1

Anatomic expression profiles of FGF-1, -4, -7, and -8 subfamilies in mouse tissues from C57/Bl6 mice. qPCR data are presented as the mean of triplicate measurements ± sd.

Figure 2

Anatomic expression profiles of FGF-9, -11, and -19 subfamilies in mouse tissues from C57/Bl6 mice. qPCR data are presented as the mean of triplicate measurements ± sd.

Figure 3

Anatomic expression profiles of FGFRs in mouse tissues from C57/Bl6 mice. qPCR data are presented as the mean of triplicate measurements ± sd.

Figure 4

Anatomic expression profile of Klotho family proteins and FGF binding protein (FGFBP1), and Lctl activity analysis. A, qPCR data are presented as the mean of triplicate measurements ± sd for tissues from C57/Bl6 mice. B, Lysates of 293 cells transfected with expression vectors for different FGFR isoforms and Flag-tagged Lctl were immunoprecipitated with Lctl using anti-Flag antibody and probed for either FGFRs using anti-V5 antibody or for Flag. Antibodies used for immunoprecipitation (ip) and immunoblotting (i.b.) are indicated. C, HEK293 cells were transfected with an expression plasmid for Flag-tagged Lctl and treated with FGF19 (1000 ng/ml), FGF21 (1000 ng/ml), FGF23 (500 ng/ml), or vehicle alone. Phosphorylated ERK (pERK), total ERK (tERK), and Flag-tagged Lctl were measured by immunoblotting. D, HEK293 cells were transfected with expression plasmids for Flag-tagged Lctl or β-Klotho and treated with FGF19 or FGF21 at the indicated concentrations. Phosphorylated ERK (pERK), total ERK (tERK), β-Klotho, and Flag-tagged Lctl were measured by immunoblotting.

Figure 5

Tissue distribution of FGFs and FGFRs in adult mouse. A, FGF expression by tissue system. B, FGFR and Klotho coreceptor expression by tissue system. Expression levels in different tissue systems are indicated. Normalized FGF mRNA expression levels were defined as absent if the cycle time value was more than 34, low if the level was below 0.01 arbitrary units, moderate if the level was between 0.01 and 0.1, and high if the level was equal to or greater than 0.1 arbitrary units. Tissue systems are defined as CNS (eye, brainstem, cerebellum, cerebrum, corpus striatum, olfactory bulb, spinal cord, hypothalamus, and pituitary), endocrine (adrenal and thyroid), GI (tongue, stomach, duodenum, jejunum, ileum, colon, pancreas, and gall bladder), metabolic (liver, kidney, brown and white adipose tissue), immune (spleen and thymus), reproductive (ovary, uterus, epididymus, preputial gland, prostate, seminal vesicles, testis, and vas deferens), respiratory (aorta, heart, and lung), and structural (muscle, bone, and skin). Tissues were pooled from C57/Bl6 mice (n = 6).

Figure 6

Cluster analysis of FGF and FGFRs. A, Unsupervised hierarchical clustering of FGFs and FGFRs based on tissue expression. qPCR data were clustered using average linkage with Pearson correlation coefficient using Matrix 1.28 software as described in Materials and Methods. B, Unsupervised hierarchical clustering of FGFRs and Klotho family coreceptors based on tissue expression. qPCR data were clustered using average linkage with Pearson correlation coefficient using Matrix 1.28 software.