The Chr X-linked Gct6 locus: A granulosa cell tumor suppressor in mice

Rabie, Zoha (2015) The Chr X-linked Gct6 locus: A granulosa cell tumor suppressor in mice. Masters thesis, Memorial University of Newfoundland.

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Abstract

Juvenile-type granulosa cell tumors (GCT) originate in the somatic tissues that surround the germ cells of the ovarian follicle in children and young women. Unlike Adult-type GCT that share a common, acquired mutation in the FOXL2 gene, the genetic determinants for juvenile-type GCT susceptibility are not so well defined. A spontaneous, early-onset GCT phenotype in SWR inbred female mice has revealed multiple Gct loci: Gct1 on Chromosome (Chr) 4 initiates the tumorigenic program; Gct4 on Chr X modifies trait penetrance and Gct6 on Chr X is a suppressor of GCT initiation. The Gct6 locus has been mapped to a 1.02 million base pair region with over 20 annotated genes. Two complementary approaches were taken to help prioritize Gct6 gene candidates. First, a congenic strain approach was taken to determine the tumor suppressor phenotype of the Gct6C57 allele in SWR.C57-X females. Second, a whole-locus capture and Next Generation Sequencing (NGS) protocol was applied to identify all nucleotide variations between SWR (tumor-susceptible SW) and Castaneus (CAST; tumor-resistant CA) alleles vs. the C57BL/6J (C57) genome. The congenic strain data supported the hypothesis that a common Gct6 tumor suppressor allele in C57 and CAST genomes was distinct from the permissive Gct6SW allele, which reduced the prioritized list of NGS variants (SNPs, INDELs) to 746. Priority was given to non-synonymous variants identified in the coding region of 5 candidate genes: BC065397, Esx1, Slc25a53, Tmsb15b1 and Tmsb15l. Sanger sequencing confirmed the 5 non-synonymous variants between C57 and SWR strains and identified a novel 28 bp deletion in the coding region of the Slc25a53 gene. Allele association analysis between 5 Gct6 permissive and 2 Gct6 suppressive strains demonstrated that the 5 non-synonymous variants were not conserved between permissive strains. However, all 5 permissive strains tested (SWR, SJL/J, PL/J, BUB/BnJ, ST/bJ) had deletion mutations with inferred deleterious frameshift effect in the Slc25a53 gene when compared to the GC tumor suppressive strains (CAST and C57), making Slc25a53 a promising candidate for shared identity with Gct6.

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