Characterization of the OmyY1 Region on the Rainbow Trout Y Chromosome

Ruth B Phillips,Suzy C P Renn,Jenefer J Dekoning,Gary H Thorgaard,Kris A Christensen,Joshua J Faber-Hammond,John D Hansen,Joseph P Brunelli

doi:10.1155/2013/261730

Abstract

We characterized the male-specific region on the Y chromosome of rainbow trout, which contains both sdY (the sex-determining gene) and the male-specific genetic marker, OmyY1. Several clones containing the OmyY1 marker were screened from a BAC library from a YY clonal line and found to be part of an 800 kb BAC contig. Using fluorescence in situ hybridization (FISH), these clones were localized to the end of the short arm of the Y chromosome in rainbow trout, with an additional signal on the end of the X chromosome in many cells. We sequenced a minimum tiling path of these clones using Illumina and 454 pyrosequencing. The region is rich in transposons and rDNA, but also appears to contain several single-copy protein-coding genes. Most of these genes are also found on the X chromosome; and in several cases sex-specific SNPs in these genes were identified between the male (YY) and female (XX) homozygous clonal lines. Additional genes were identified by hybridization of the BACs to the cGRASP salmonid 4x44K oligo microarray. By BLASTn evaluations using hypothetical transcripts of OmyY1-linked candidate genes as query against several EST databases, we conclude at least 12 of these candidate genes are likely functional, and expressed.

Highlights

Salmonid fishes have the XX/XY system of sex determination [1]
The SEX locus is not found on a common linkage group in Pacific salmon and trout, but rather each species has the SEX locus on a different linkage group as shown by genetic mapping and localization of male-specific markers using in situ hybridization with clones to GH-Y [7,8,9]. (Rainbow and cutthroat trout are an exception to this [10], and hybrids between these two species are interfertile.) it is possible that each species has a different master sex determining gene, this is unlikely because there are several male-specific markers shared by the Oncorhynchus species
We present evidence based on sequence information of BAC clones isolated from the OmyY1 region of rainbow trout that there are a number of sex-linked genes shared between the X and Y chromosomes, implying the sex chromosomes are in the early stages of differentiation

Summary

Introduction

Salmonid fishes have the XX/XY system of sex determination [1]. Most rainbow trout have morphologically distinguishable sex chromosomes [2], with the short arm being longer in the X chromosome than the Y, primarily due to presence of 5S rDNA sequences on the X chromosome (reviewed in [3]). (Rainbow and cutthroat trout are an exception to this [10], and hybrids between these two species are interfertile.) it is possible that each species has a different master sex determining gene, this is unlikely because there are several male-specific markers shared by the Oncorhynchus species These include OmyY1, found in all Pacific trout and salmon [11], OtY2 [12] which is related to OmyY1, and GH-Y [13], which are found in most species of Pacific salmon, and OtY1, found only in Chinook salmon [14]. These results support the hypothesis that a small chromosomal segment containing the SEX locus, or the small short arm containing the SEX locus, is transposing to a new chromosome in each of these species (reviewed in [9, 15])

Methods

Discussion

Conclusion