Proteomics 2012, 12, 1949–1956 1949 DOI 10.1002/pmic.201100500 DATASET BRIEF Identification and characterization of highly expressed proteins in sperm cells of the marine mussel Mytilus edulis Angel P. Diz 1 , Edward Dudley 2 and David O. F. Skibinski 2 1 Department of Biochemistry, Genetics and Immunology, Faculty of Biology, University of Vigo, Vigo, Spain 2 Institute of Life Sciences, College of Medicine, Swansea University, Swansea, United Kingdom Proteomic analysis on sperm has been restricted to only a few model organisms. We present here a 2DE PAGE proteome map of sperm cells from a nonmodel organism, the marine mussel Mytilus edulis, a free-spawning marine invertebrate with external fertilization. Ninety- six protein spots showing high expression were selected and of these 77 were successfully identified by nESI–MS analysis. Many of the identifications are relevant to sperm cell physiology and mtDNA functioning. The results and proteomics approach used are discussed in relation to their potential for advancing understanding of the unusual system of mtDNA inheritance described in Mytilus spp., and for the testing of evolutionary hypotheses pertaining to the role of fertilization in the speciation process. Keywords: Cell biology / DUI / Evolution / Fertilization / Proteome / Speciation Received: September 21, 2011 Revised: February 3, 2012 Accepted: March 26, 2012 Sperm are highly differentiated cells with very marked func- tional differences from other cell types reflecting important roles in fertilization, embryo development, and heredity [1]. Sperm DNA may be transcriptionally active, and sperm might play roles other than transporting the paternal genome to the oocyte during fertilization [1–3]. Thus, the sperm cell is a good candidate for proteomic analyses [3, 4]. To date, only a few proteomics studies have been described in sperm cells, all in model organisms with fully sequenced genomes, i.e. in mammals (human, mouse, rat, cow, and boar), inverte- brates (fruit fly, honeybee, the nematode Caenorhabditis el- egans and the ascidian Ciona intestinalis), and germ cells of plants (pollen of rice and tomato) [1]. To our knowledge, the ascidian sperm proteome provides the only example from a marine organism. Comparative analysis of the sperm pro- teome may improve understanding of both conserved and Correspondence: Dr. Angel P. Diz, Department of Biochemistry, Genetics and Immunology, Faculty of Biology, University of Vigo, 36310, Vigo, Spain E-mail: angel.p.diz@uvigo.es Fax: 34 986813828 Abbreviations: ATP, adenosine triphosphate; DUI, doubly uni- parental inheritance; GO, gene ontology; TCA, tricarboxylic acid variable processes in different taxa, and advance the study of the molecular mechanisms underlying specific sperm func- tion in organisms with different reproductive strategies. At the molecular level, this might contribute to a deeper knowl- edge of adaptive and evolutionary strategies used by different taxa, and give insights into the speciation process itself. The blue mussel (Mytilus spp.), a marine bivalve mollusc, is of particular interest because of its unusual system of mi- tochondrial DNA inheritance [5–8], referred to as doubly uni- parental inheritance (DUI). This is characterized by the pres- ence of distinct gender-associated mtDNAs, which are inher- ited either maternally (F mtDNA) or paternally (M mtDNA). DUI provides an interesting evolutionary scenario because this mechanism of inheritance opens the opportunity for se- lection to act directly on the mtDNA of the sperm [9, 10], which does not happen in organisms with standard maternal inheritance of mtDNA. Fluorescent staining of mitochondria has been used to study the behavior of sperm mitochondria in embryos following fertilization [11 and references therein]. These studies suggest that in embryos destined to produce males, the sperm mitochondria remain in close proximity to each other as far as the eight-cell stage and end up in Colour online: See the article online to view Fig. 2 in colour. C  2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.proteomics-journal.com