The Many Faces of Carbohydrate Metabolism in Male Germ Cells: From Single Molecules to Active Polymers

Spermatogenesis is a complex physiological process that involves cell proliferation, meiotic division and a final cell differentiation of post-meiotic cells into spermatozoa. During this process male germ cells also undergo a metabolic differentiation process, in which post-meiotic spermatogenic cells (spermatids) but not meiotic spermatogenic cells (spermatocytes) respond differentially to D-glucose metabolism, glucose transporters (GLUTs) distribution and utilization of non-hexose substrates, such as lactate/pyruvate or dihydroxyacetone. These differences might be explained by the requirement for a specific metabolic process to support cell differentiation or in some cases, cell viability. In addition, though glycogen is considered to be the main glucose store, in male germ cells this polymer may play a novel role in cell proliferation, acting as a new marker for apoptotic events in testicular tissue via a yet unknown mechanism. In this article, we summarize the main metabolic changes that occur during male germ differentiation, with a specific focus on metabolic sources during spermatocyte to spermatid transition. The latter considering that these cells come from the same cell linage as specialized cells, but are not isolated from their environment, describing the roles from single molecules to polymers on the viability of male germ cells.

Differential signalling for enhanced hexose uptake by interleukin (IL)-3 and IL-5 in male germ cells

We studied the expression and function of the IL (interleukin)-3 and IL-5 family of receptors in male germ cells. RT (reverse transcription)-PCR showed expression of mRNAs encoding the alpha and beta subunits of the IL-3 and IL-5 receptors in human testis, and the presence of IL-3 and IL-5 receptors alpha and beta proteins was confirmed by immunoblotting with anti-alpha and anti-beta antibodies. The immunolocalization studies showed expression of these receptors in the germ line in the human testis and in human and bovine ejaculated spermatozoa. Functional studies with bull spermatozoa indicated that IL-3 signalled for increased uptake of hexoses in these cells at picomolar concentrations compatible with expression of functional high-affinity IL-3 receptors in these cells. In contrast, IL-5 failed to induce increased hexose uptake in bull spermatozoa. Experiments using HL-60 eosinophils that express functional IL-3 and IL-5 receptors confirmed that IL-3, but not IL-5, signalled for increased hexose uptake. Our findings suggest that differential signalling for increased hexose uptake by heteromeric high-affinity IL-3 and IL-5 receptors in mammalian spermatozoa is a property that depends on the identity of the alpha-subunit forming part of the alphabeta-complex and is not a property specific to the germ cells.

Isoacceptor glycine tRNA species during bovine myocardium development

The isoacceptor patterns of glycyl-tRNAs from fetal bovine myocardium during development, and of adult cardiac muscle, have been studied by reverse-phase chromatography. 4 isospecies were detected and quantitative changes in their relative abundance were noted. Moreover, upon testing their efficiency in transferring glycine into polypeptides a differential utilization of the cognate tRNAs was observed.