Analytical Techniques: Microarray Technology as a Diagnostic Tool
Microarrays and other innovative technologies are a wide range of new techniques that are used to unveil causes of infertility, for example, the Polscope and atomic force microscopy for the detailed study of sperm morphology and structure, and microfluidics that quickly isolates good morphology spermatozoa from poor-quality spermatozoa.24 Today, it is well known that, as well as supplying DNA, the spermatozoon also provides the egg with paternal centrioles, proteins, and RNA.25 Although the functional significance of mRNA in mature spermatozoa remains essentially unexplored,26 it is known that sperm mRNA is necessary from the moment of the first embryo cleavage until the activation of the embryonic genome27 and may influence the phenotypic traits of the embryo28 and offspring.29 Since its introduction in 1994, microarray technology has made significant advances in the identification and characterization of novel or known genes correlated with male infertility in mice and humans.30
Molecular biology techniques as microarrays allow the analysis of thousands of genes, proteins, or metabolites at a time and have allowed the scale of biologic research to be expanded from the study of single genes or proteins to a systematic study of all genes and proteins. They provide a global view of biological processes, being of particular interest to molecular medicine, where they have thousands of potential applications. Among the different available ‘‘omics’’ platforms, complementary DNA (cDNA) microarrays, which measure mRNA transcript levels, are of particular interest given the previously mentioned relevance of paternal mRNA for reproductive success. Transcriptomics is the study of the mRNA pool expressed in a cell at a particular time under determined conditions.31 This technique has recently been applied to sperm evaluation.8-32-34
These platforms provide a list of genes whose expression has been detected in a sample, pool, or group, as well as the fold change or exclusivity of gene expression when two biological situations are compared. With the help of different bioinformatic tools, an ontological interpretation of the results can be obtained from current molecular knowledge and databases, which include lists of cellular components, biological processes, and molecular functions that are regulated by a significant number of the genes that are underexpressed or overexpressed.32-34
The aim of this chapter is to deepen our knowledge about one of those sperm molecular feature candidates to be involved in pregnancy success: the mRNA content (transcriptome) of spermatozoa that achieved successful fertilization and implantation versus spermatozoa that did not achieve successful fertilization and implantation in different assistive reproductive technologies (ARTs).