Characterization of the Expression and Regulation of Genes Necessary for myo-Inositol Biosynthesis and Transport in the Seminiferous Epithelium1

Abstract

In many mammals, the concentration of myo-inositol in the fluid of the seminiferous tubules is dramatically higher than levels found in serum. Two enzymes involved in myo-inositol synthesis: myo-inositol-1-phosphate synthase (ISYNA1) and myo-inositol monophosphatase-1 (IMPA1), are known to have high activity in the testes. ISYNA1 is an isomerase that catalyzes the conversion of glucose-6-phoshate to myo-inositol-1-phosphate. IMPA1 then hydrolyzes the phosphate group to produce myo-inositol. Although no physiological role for the high concentration of myo-inositol has yet to be elucidated, it has been suggested that it could be involved in osmoregulation. Previous research on these enzymes in the testis has focused on enzyme activity. The objective of this study was to evaluate the expression of these genes and the myo-inositol transporter, Slc5a3, within the testis. Using Northern blot analyses, we found that all three genes, Impa1, Isyna1, and Slc5a3 are expressed in Sertoli cells. Isyna1 is highly expressed in two types of germ cells, pachytene spermatocytes and round spermatids. IMPA1 was expressed in round spermatids. Slc5a3 expression is upregulated when Sertoli cells are treated with 0.1 mM dibutyryl cAMP. When Sertoli cells were cultured in a hypertonic medium, there was an increase in the expression of Isyna1 and Slc5a3. We postulate that this upregulation is a result of the capability of the Sertoli cell to sense and then react to a change in osmolarity by increasing the transport and production of the osmolyte myo-inositol.

Implication of transcriptome profiling of spermatozoa for stallion fertility

“…Myoinositol is produced by two enzymatic steps from glucose-6-phosphate, and its synthesis is regulated by myoinositol-1-phosphate synthase and myoinositol monophosphatase-1. These activity of these two enzymes is high in the testes (Chauvin and Griswold 2004). These findings support our identification of myoinositol within the top metabolic pathways in the present study.…”

“…In addition, inositols have been reported to affect different processes involved in oocyte fertilisation, which improve the penetration of the ovum cumulus oophorus, binding with the zona pellucida and the acrosome reaction (Calogero et al 2015). Furthermore, high concentrations of myoinositol have been found in the fluid of the seminiferous tubule in many mammals (Setchell et al 1968;Hinton et al 1980;Chauvin and Griswold 2004). Myoinositol is produced by two enzymatic steps from glucose-6-phosphate, and its synthesis is regulated by myoinositol-1-phosphate synthase and myoinositol monophosphatase-1.…”

Mapping of the Human Testicular Proteome and its Relationship With That of the Epididymis and Spermatozoa

“…The enzymatically active ISYNA1 has long been known to be present in the rat testis (32,33) and ovine testicular, but not ejaculated, spermatozoa, which can convert glucose to myo-inositol in vitro (34). In mice the ISYNA1 gene is transcribed by isolated primary spermatocytes and round spermatids (35). The present finding on the absence of this protein from human spermatids warrants investigation as a species difference.…”

Knockout mice in understanding the mechanism of action of lithium

“…There are three major sources of intracellular myo-inositol: recycling in the phosphatidylinositol cycle, de novo synthesis from glucose 6-phosphate by myo-inositol-1-phosphate synthase and IMPase, and uptake from extracellular fluid [8,9]. Dietary myo-inositol is an important source of intracellular inositol.…”