Chromatin and gene organization during spermatogenesis and early developement: An evolutionary perspective

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Spermatogenesis is a cell differentiation process leading to the formation of the male gametes (spermatozoa). The deoxyribonucleic acid (DNA) of sperm cells is associated with a set of highly basic proteins called protamines. This contrasts the rest of the body, including eggs, in which the DNA is associated with a broad spectrum of nuclear proteins such as core histones, linker histones and non-histone proteins. In both instances, the resulting protein-DNA complexes are called chromatin. During spermatogenesis, histones of chromatin from the stem cells are replaced in the mature sperm by sperm-specific histones (H), protamines (P), or protamine-like proteins (PL), which have an intermediate chemical composition between H and P. This histone replacement process is reverted during fertilization of the egg by the sperm. The molecular mechanisms involved in these chromatin rearrangements are poorly understood. The long-term objective of this research is to describe and understand the structural changes and factors involved in the chromatin modifications during spermatogenesis and after fertilization. To facilitate this, we have selected several invertebrate and vertebrate organisms, with high levels of gametes, for analysis. This research has a two-fold interest. From an applied perspective, the understanding of these chromatin transitions could enlighten society on human infertility problems, sperm competition, and speciation in other organisms. From an academic perspective, the analysis and characterization of the genes and corresponding proteins involved in these processes, in different organisms, provide a unique opportunity to study their evolution.