Finding genes that determine variation in sperm morphology and motility

Across different animal taxa, sperm are perhaps the most diverse of all types of cell. However, in all species they have one principal function; to fertilise an egg. In many different biological and medical sub-disciplines there has been considerable interest in how sperm morphology can influence sperm motility (swimming speed) and fertility. We probably all have a 'cartoon' image of sperm with the longest tail swimming faster than sperm with short tails. Therefore, it is perhaps surprising that within most organisms where people have looked at the relationship between sperm length and sperm motility they have either failed to find any relationship, or have only found a relationship with particular components of the sperm (e.g. the head, the midpiece). In our study organism, the zebra finch, which is an important model organism in neurobiology and behavioural ecology, we have shown that there is considerable inter-male variation in sperm traits, but that within males sperm morphology and motility are highly repeatable. We have also demonstrated that males with long sperm have the fastest sperm, and that both sperm length and sperm speed are heritable. Finally (and uniquely) we have shown that there is a genetic correlation between sperm length and sperm motility, which strongly suggests that the relationship is causative rather than because both sperm traits are simultaneously influenced by environmental factors (e.g. diet, condition). While investigating zebra finch sperm biology we have also been at the forefront of the development of zebra finch genomics tools. For example, we constructed the first zebra finch genetic linkage map and we were part of an international team that sequenced and assembled the zebra finch genome. In this project we will integrate the two strands (sperm biology and genomics) of our previous zebra finch work. We will perform genome-wide association studies (GWAS) to map and identify the genes responsible for inter-male differences in sperm morphology and motility. Genes responsible for differences in sperm motility have not yet been identified in any species. We will do this by developing a chip that probes 20,000 genetic markers at once and typing 1000 male birds (of known sperm morphology/motility) with the chip. We will also sequence the transcriptome (which contains the part of the genome that encodes proteins) from the testes of 20 males with short sperm and 20 males with long sperm. These males come from our existing selection lines which already show a large difference in sperm length. By integrating the GWAS and the transcriptomics data we will provide the first ever description of the genes that determine variation in sperm morphology and motility. Therefore, our findings will be relevant to researchers in human fertility medicine, animal breeding/agriculture, conservation biology and evolutionary biology.

The overall aim of this proposal is to identify the genes responsible for variation in sperm traits in the zebra finch. We will do this by employing cutting-edge genomics tools to type 20,000 SNP markers in ~1,000 birds. We will then perform a genome-wide association study (GWAS) to map the genes responsible for inter-male differences in sperm morphology and motility, which are both known to be heritable in our population. The SNPs will be selected from the 1.7M zebra finch SNPs in the public domain and will be chosen to cover the entire genome, while accounting for the heterogeneity in linkage disequilibrium (LD) that we earlier described in the zebra finch genome. The SNPs will be typed using Illumina Infinium beadchips and we will outsource genotyping to an external provider (we recently obtained quotations from 6 UK-based providers). The beadchips will be an essential gene mapping resource to the entire zebra finch genomics community and other users will be able to purchase additional chips. Genotype data will be managed using the PLINK software (which is ideal for quality control checking, summary statistic generation and more sophisticated population genetic tests) and GWAS tests will be performed using EMMAX. The birds we will type are part of our long-running (~20 years) aviary population and most individuals have already been measured for sperm traits. More recently we have established selection lines for long and short sperm, and have seen a strong response to selection, especially in the long-sperm line. Using Illumina sequencing technology we will sequence the testis transcriptome of 20 birds from each of the long and short lines. Gene expression will be compared between the two lines, and we will test for associations between (i) gene expression, (ii) SNPs within the transcriptome and (iii) sperm morphology/motility. These results will be integrated with the GWAS results to provide further dissection of the genetic basis of variation in sperm traits.

Our project addresses fundamental questions in evolutionary genetics; as such it is largely blue-skies research and will advance understanding of the genetic architecture of quantitative genetic variation. However, the genetics of sperm morphology and motility are of relevance to many areas of biology and medicine and our research has the potential to indirectly make a societal and economic impact. Apart from standard activities (attending conferences, publishing our research, and presenting scientific seminars) we intend to engage in the following impact activities: (i) Computer-assisted semen analysis (CASA) workshop. We will run this workshop immediately after the 2013 Biology of Spermatozoa meeting and hold it in Sheffield. It will be aimed at non-academics that stand to benefit from technology to measure sperm parameters (especially motility). For example, this might include animal breeding/livestock improvement companies, conservation managers/zookeepers and the equine industry. We will also provide training (and scripts) on how to analyse the data using the free statistics software R. Funding is requested to cover travel and subsistence costs. (ii) Training for the Graduate RA and Postdoctoral RA. The University of Sheffield is committed to knowledge exchange and societal/economic impact. The research staff on this project will be given opportunities to develop their understanding and awareness of innovation and the translational skills, with support from the investigators and the Research and Innovation Services officers, and within a broader programme of training. (iii) Outreach We will explain our science to the public via the media, public science events including literary/book festivals and through UCAS visit days. We demonstrate CASA technology to over 1000 visitors to the department every year, showing them video of high and low motility sperm samples. (iv) Creation of a SNP chip The SNP chip we will develop will be commercially available to other users via the provider Illumina, a global company with a UK headquarters.