Nitric oxide and cyclic nucleotides: Their roles in junction dynamics and spermatogenesis

Spermatogenesis is a highly complicated process in which functional spermatozoa (haploid, 1n) are generated from primitive mitotic spermatogonia (diploid, 2n). This process involves the differentiation and transformation of several types of germ cells as spermatocytes and spermatids undergo meiosis and differentiation. Due to its sophistication and complexity, testis possesses intrinsic mechanisms to modulate and regulate different stages of germ cell development under the intimate and indirect cooperation with Sertoli and Leydig cells, respectively. Furthermore, developing germ cells must translocate from the basal to the apical (adluminal) compartment of the seminiferous epithelium. Thus, extensive junction restructuring must occur to assist germ cell movement. Within the seminiferous tubules, three principal types of junctions are found namely anchoring junctions, tight junctions, and gap junctions. Other less studied junctions are desmosome-like junctions and hemidesmosome junctions. With these varieties of junction types, testes are using different regulators to monitor junction turnover. Among the uncountable junction modulators, nitric oxide (NO) is a prominent candidate due to its versatility and extensive downstream network. NO is synthesized by nitric oxide synthase (NOS). Three traditional NOS, specified as endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS), and one testis-specific nNOS (TnNOS) are found in the testis. For these, eNOS and iNOS were recently shown to have putative junction regulation properties. More important, these two NOSs likely rely on the downstream soluble guanylyl cyclase/cGMP/protein kinase G signaling pathway to regulate the structural components at the tight junctions and adherens junctions in the testes. Apart from the involvement in junction regulation, NOS/NO also participates in controlling the levels of cytokines and hormones in the testes. On the other hand, NO is playing a unique role in modulating germ cell viability and development, and indirectly acting on some aspects of male infertility and testicular pathological conditions. Thus, NOS/NO bears an irreplaceable role in maintaining the homeostasis of the microenvironment in the seminiferous epithelium via its different downstream signaling pathways

The adult stem cells are progeny of the microvascular pericytes

This review concerns the origin of the adult stem cells. The adult stem cells show a narrow relationship with the blood vessels. In 2004 we discovered that the testicular neuroendocrine Leydig cells originate from the periendothelial pericytes of the microvasculature. Since then, numerous publications appeared that indicated similar relationships in most if not all mammalian organs. Thus, our results and the results of the literature provide unequivocal evidence that the ancestors of the adult stem cells are the microvascular pericytes. The following points support this view:1. The pericytes are the only cell type that is situated in true vascular niches.2. The pericytes possess pluripotent qualities. They give progeny of all three germinal layer cells (ectoderm, mesoderm and endoderm). Thus the pericytes originate very early in the embryonal development from epiblast, together with the primitive germ cells.3. Following activation the resting, sleeping pericytes start to divide, show self renewal and release daughter cells that migrate toward the perivascular space.4. These cells undergo a fast transdifferentiation and as transit amplifying cells, depending on the different environmental factors, start to differentiate into different cell phenotypes, inclusive perivascular mesenchymal stem cells.5. The neural crest stem cells arise later from the ectoderm, after the vasculature, and are multipotent (not pluripotent) stem cells.Conclusion: During the evolution the nature has developed a very effective adult stem cell reserve system. Namely, very early pluripotent stem cells are delaminated and disseminated along with the developing blood vessels in all tissues and organs where they remain saved as pericytes in true vascular niches as resting (resereve) cells needed for physiological repair, pathological regeneration and even cancer stem cells of the adult organism

Male germ cells and photoreceptors, both dependent on close cell-cell interactions, degenerate upon ClC-2 Cl(-) channel disruption

The functions of some CLC Cl(-) channels are evident from human diseases that result from their mutations, but the role of the broadly expressed ClC-2 Cl(-) channel is less clear. Several important functions have been attributed to ClC-2, but contrary to these expectations ClC-2-deficient mice lacked overt abnormalities except for a severe degeneration of the retina and the testes, which led to selective male infertility. Seminiferous tubules did not develop lumina and germ cells failed to complete meiosis. Beginning around puberty there was a massive death of primary spermatocytes and later also of spermatogonia. Tubules were filled with abnormal Sertoli cells, which normally express ClC-2 in patches adjacent to germ cells. In the retina, photoreceptors lacked normal outer segments and degenerated between days P10 and P30. The current across the retinal pigment epithelium was severely reduced at P36. Thus, ClC-2 disruption entails the death of two cell types which depend on supporting cells that form the blood-testes and blood-retina barriers. We propose that ClC-2 is crucial for controlling the ionic environment of these cells

Nitric Oxide and Cyclic Nucleotides: Their Roles in Junction Dynamics and Spermatogenesis

Spermatogenesis is a highly complicated process in which functional spermatozoa (haploid, 1n) are generated from primitive mitotic spermatogonia (diploid, 2n). This process involves the differentiation and transformation of several types of germ cells as spermatocytes and spermatids undergo meiosis and differentiation. Due to its sophistication and complexity, testis possesses intrinsic mechanisms to modulate and regulate different stages of germ cell development under the intimate and indirect cooperation with Sertoli and Leydig cells, respectively. Furthermore, developing germ cells must translocate from the basal to the apical (adluminal) compartment of the seminiferous epithelium. Thus, extensive junction restructuring must occur to assist germ cell movement. Within the seminiferous tubules, three principal types of junctions are found namely anchoring junctions, tight junctions, and gap junctions. Other less studied junctions are desmosome-like junctions and hemidesmosome junctions. With these varieties of junction types, testes are using different regulators to monitor junction turnover. Among the uncountable junction modulators, nitric oxide (NO) is a prominent candidate due to its versatility and extensive downstream network. NO is synthesized by nitric oxide synthase (NOS). Three traditional NOS, specified as endothelial NOS (eNOS), inducible NOS (iNOS), and neuronal NOS (nNOS), and one testis-specific nNOS (TnNOS) are found in the testis. For these, eNOS and iNOS were recently shown to have putative junction regulation properties. More important, these two NOSs likely rely on the downstream soluble guanylyl cyclase/cGMP/protein kinase G signaling pathway to regulate the structural components at the tight junctions and adherens junctions in the testes. Apart from the involvement in junction regulation, NOS/NO also participates in controlling the levels of cytokines and hormones in the testes. On the other hand, NO is playing a unique role in modulating germ cell viability and development, and indirectly acting on some aspects of male infertility and testicular pathological conditions. Thus, NOS/NO bears an irreplaceable role in maintaining the homeostasis of the microenvironment in the seminiferous epithelium via its different downstream signaling pathways