Molecular biological features of male germ cell differentiation

Abstract

Somatic cell differentiation is required throughout the life of a multicellular organism to maintain homeostasis. In contrast, germ cells have only one specific function; to preserve the species by conveying the parental genes to the next generation. Recent studies of the development and molecular biology of the male germ cell have identified many genes, or isoforms, that are specifically expressed in the male germ cell. In the present review, we consider the unique features of male germ cell differentiation. (Reprod Med Biol 2007; 6: 1-9).

Keywords: gene; germ cell; infertility; single nucleotide polymorphisms; spermiogenesis; testis.

Figure 1

Schematic representation of the regulatory pathways affecting gene expression during mouse spermatogenesis. ¹ Spermatids are connected by intercellular bridges. The pathway of transcriptional control by CREM‐τ is shown in green. RNA‐binding proteins or poly(A)‐RNA polymerases modify the translation of transcribed mRNAs, which are then transferred to the cytoplasm along microtubules by the kinesin KIF17b (red). Some mRNAs are transferred to another cell through the intercellular bridge (blue). The timing of translation is regulated by RNA‐binding proteins (yellow). Circles indicate proteins, T.C. indicates the transcriptional complex, and the boxed Y and H indicate Y‐ and H‐elements on the mRNA, respectively. Bars indicate microtubule networks, and arrows show the direction of movement of protein and protein‐mRNA complexes. Doublet boxes and circles indicate cell membranes and nuclear membranes, respectively.

Figure 2

Schematic representation of the differentiation lineage of germ cells in the constitution of the individual. The left column shows the ‘Distinctive evolutionary model’ in which the gamete that carries genes to the next generation differentiates into organ A in the embryo, and next differentiates into gametes. The right column shows the ‘Equal evolution model’ in which the gamete differentiates from the embryo independent of other cells. In the left model, the differentiation of organ A is indispensable for the gamete. The criteria for the evolution of cell differentiation (A and G) in the left model are more complex than in the right model because it is necessary to serve purposes in two forms of cell differentiation (A and G). In the right model, evolution is almost equal between germ cell differentiation and other cell differentiation (the lowest boxes). The upper red circle represents a multipotent fertilized egg. The fertilized egg undergoes embryonic growth and forms an individual that consists of various differentiated organs and specific differentiated cells (A–D). The cell with the ability to differentiate into a gamete is shown in G. Red arrows indicate the lineage of germ cell differentiation.