We have used data from genome-wide association studies (GWAS) to gain insight into the regulation of the human growth plate. Recent GWAS have identified 180 loci associated with human height. We reasoned that many of the causative genes within these loci influence height because they are expressed in and function in the growth plate, a cartilaginous structure that causes elongation of long bones and vertebral bodies and thus determines height. Therefore these GWAS could reveal genes that play an important role in human growth plate chondrogenesis. However, the GWAS data generally do not pinpoint a single gene at each locus but instead identify a set of contiguous genes, only one of which presumably modulates height. Therefore, to identify genes that contribute to human height variation by acting in the growth plate, we used human disease databases, a mouse knockout phenotype database, and expression microarray studies of mouse and rat growth plate to identify genes that are likely required for normal growth plate function, and then we searched for these growth plate-related genes within the height-determining loci defined by GWAS. Individually, each of these approaches identified significantly more genes within the GWAS height loci than at random genomic locations, supporting the validity of the approach. Together, these functional and expression analyses implicated 78 genes from the GWAS loci, including multiple genes involved in IHH-PTHrP, BMP, CNP, and GH-IGF1 signaling. In addition, the analysis identified many genes not previously known to regulate the growth plate. Thus, this analysis implicated a large number of genes that regulate human growth plate chondrogenesis and thereby contribute to the normal variation in human height. Because uncommon deleterious mutations in these genes would be expected to disrupt growth plate function more severely, genes emerging from this analysis are strong candidates for the etiology of idiopathic short stature and skeletal dysplasias. The identified genes also suggest new regulatory pathways in the growth plate, inviting functional investigation. In other studies, we explored the relationship between the mechanisms that progressively slow growth of normal tissues during childhood and the mechanisms that allow excessive growth of malignant tissues. In many normal tissues, proliferation rates decline postnatally causing somatic growth to slow. Previous evidence suggests that this decline is due in part to declining expression of growth-promoting imprinted genes including Mest, Plagl1, Peg3, Dlk1, and Igf2. Embryonal cancers are composed of cells that maintain embryonic characteristics and proliferate rapidly in childhood. We hypothesized that the abnormal persistent rapid proliferation in embryonal cancers occurs in part because of abnormal persistent high expression of growth-promoting imprinted genes. Analysis of microarray data showed elevated expression of MEST, PLAGL1, PEG3, DLK1, and IGF2 in various embryonal cancers, especially rhabdomyosarcoma, compared to non-embryonal cancers and normal tissues. Similarly, mRNA expression, assessed by real-time PCR, of MEST, PEG3, and IGF2 in rhabdomyosarcoma cell lines was increased compared to non-embryonal cancer cell lines. Furthermore, siRNA-mediated knockdown of MEST, PLAGL1, PEG3, and IGF2 expression inhibited proliferation in Rh30 rhabdomyosarcoma cells. These finding suggest that the normal postnatal downregulation of growth-promoting imprinted genes fails to occur in some embryonal cancers, particularly rhabdomyosarcoma, and contributes to the persistent rapid proliferation of rhabdomyosarcoma cells, and, more generally, that failure of the mechanisms responsible for normal somatic growth deceleration can promote tumorigenesis.
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