Spermatogonial Stem Cell Renewal Research Articles

Molecular control mechanisms of fish spermatogenesis

Fish spermatogenesis, from spermatogonial stem-cell renewal to sperm maturation, is controlled by the sex steroid hormones. Mitotic divisions of spermatogonia can be categorized by spermatogonial stem cell renewal and spermatogonial proliferation. Spermatogonial renewal is regulated by estradiol-17β (E2; the natural estrogen in vertebrates), and spermatogonial proliferation toward meiosis is promoted by 11-ketotestosterone (11-KT), the main androgen in teleost. The action of E2 and 11-KT is mediated by other factors produced by Sertoli cells; E2 is mediated by spermatogonial stem-cell renewal factor and 11-KT is mediated by spermatogenesis preventing substance and activin B. Although 11-KT also induce meiosis and spermiogenesis, the control mechanisms of these processe are not clear. After spermiogenesis, immature spermatozoa undergo sperm maturation. Sperm maturation is regulated by 17α,20β-dihydroxy-4-pregnen-3-one (DHP), which is progestin in teleost. The DHP acts directly on spermatozoa to active the carbonic anhydrase existed in the spermatozoa. This enzymatic activation causes an increase in the seminal plasma pH, enabling spermatozoa to motile.

Germ cell failure is the cause of luxoid (Lu) mouse mutant defective spermatogenesis

Objective: Spermatogonial stem cells continue to renew and differentiate throughout the lifespan. Successful male reproduction requires proper regulation and balance of these two pathways. Disruptions of the mechanisms that affect spermatogonial stem cell activity can contribute to male infertility. The well known luxoid mouse mutation has been described as altering the balance between spermatogonial stem cell renewal and differentiation. It is unclear what testicular cell type is affected by the luxoid defect. This study determined whether the defect in spermatogenesis is due to a failure of the somatic component of the testis or due to an intrinsic problem of the germ line stem cell.

Japanese Eel: A Model for Analysis of Spermatogenesis

The Japanese eel has two characteristics advantageous for the study of the mechanisms controlling spermatogenesis. One is the possibility of artificial induction of the complete process of spermato-genesis from spermatogonial proliferation to spermiogenesis by exogenous gonadotropin injection, and the other is the possibility of inducing this process in an in vitro testicular organ culture or germ-Sertoli cell coculture system. Using the eel system, we analyzed the control mechanisms of spermatogenesis. In Japanese eel, the whole process of spermatogenesis is regulated by several sex steroid hormones. Spermatogonial stem cell renewal is promoted by estradiol-17β (the natural estrogen in vertebrates). Spermatogonial proliferation can be induced by 11-ketotestosterone, the main androgen in teleost. IGF-I is necessary for the action of 11-ketotestosterone in the initiation of spermatogenesis. The action of 11-ketotestosterone is mediated by other factors, such as activin B, produced by Sertoli cells. Although 11-ketotestosterone also induce meiosis and spermiogenesis, the control mechanisms of these processes are not clear. After spermiogenesis, immature spermatozoa undergo sperm maturation, thereby becoming capable of fertilization. Sperm maturation is regulated by 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-DP), which is progestogen in teleosts. The 17α,20β-DP acts directly on spermatozoa to activate the carbonic anhydrase existed in the spermatozoa. This enzymatic activation causes an increase in the seminal plasma pH, enabling spermatozoa to motile.

Estradiol-17β Stimulates the Renewal of Spermatogonial Stem Cells in Males

In this work, we examined the functions of the female hormone “estrogen” on spermatogenesis of the Japanese eel (Anguilla japonica). Estradiol-17β (E2), a natural estrogen in vertebrates, was present in the serum and its receptor was expressed in the testis during the whole process of spermatogenesis. Spermatogonial stem cell renewal was promoted by E2 implantation but was suppressed by tamoxifen (an antagonist of estrogen). In vitro, 10 pg/ml of E2 was sufficient to induce spermatogonial stem cell division in cultured testicular tissue, therefore confirming the in vivo observations. These results clearly show that estrogen is an indispensable “male hormone” in the early spermatogenetic cycle.

Spermatogonial stem cells

The mammalian seminiferous epithelium consists of a highly complex yet well-organized cell population, with germ cells in mitosis and meiosis and postmeiotic cells undergoing transformation to become spermatozoa. To study the factors which control renewal and differentiation of spermatogonial stem cells, animal models are now available which allow for arrest and restart of spermatogonial differentiation. In addition, marked progress has been made in understanding the control of apoptosis and its role in spermatogonia. For the future, spermatogonial stem cell transplantation may have important practical applications.

A quantitative study of spermatogonial multiplication and stem cell renewal in the C3H/101 F 1 hybrid mouse

In whole mounts of seminiferous tubules of C3H/101 F 1 hybrid mice, spermatogonia were counted in various stages of the epithelial cycle. Furthermore, the total number of Sertoli cells per testis was estimated using the disector method. Subsequently, estimates were made of the total numbers of the different spermatogonial cell populations per testis. The results of the cell counts indicate that the undifferentiated spermatogonia are actively proliferating from stage XI until stage IV. Three divisions of the undifferentiated spermatogonia are needed to obtain the number of A 1 plus undifferentiated spermatogonia produced each epithelial cycle. Around stage VIII almost two-thirds of the A pr and all of the A al spermatogonia differentiate into A 1 spermatogonia. It was estimated that there are 2.5 × 10 6 differentiating spermatogonia and 3.3 × 10 5 undifferentiated spermatogonia per testis. There are about 35,000 stem cells per testis, constituting about 0.03% of all germ cells in the testis. It is concluded that the undifferentiated spermatogonia, including the stem cells, actively proliferate during about 50% of the epithelial cycle.

Spermatogonial stem cell renewal in the mouse. II. After cell loss.

ABSTRACTThe repair of the mouse seminiferous epithelium after cell loss has been studied in seminiferous tubules mounted in toto. Cell loss was inflicted by injection of Myleran in a dose of 10 mg/kg body weight. In stages 7–8, in which we mainly counted, the numbers of Aisolated (Ais), Apaired (Apr), Aaligned (Aal) and A1 spermatogonia and resting primary spermatocytes decreased after injection. After about 24 days normal numbers of A1 spermatogonia were found again. Thereafter a substantial overshoot in the number of A1 spermatogonia was found.While normally most of the Apr and Aal cells differentiate into A1 spermatogonia in stages 3 and 4 and do not divide until stage 9, during repair they pass through one more division during stages 6 and 7. Normally, during these stages divisions of these spermatogonia are rare. Owing to this extra division the transformation of Apr and Aal into A1 spermatogonia is delayed from stage 3 or 4 to stage 8, i.e. still before stage 9, in which A1 spermatogonia divide. From 16 days after the injection onwards the extra division takes place less generally and more and more cells transform into A1 spermatogonia at the normal time.

Spermatogonial stem cell renewal in the mouse. I. Normal situation.

ABSTRACTSpermatogenesis in the mouse has been investigated by counting the different kinds of spermatogonia throughout the cycle of the seminiferous epithelium. A description is given of the Aisolated (Ais), Apaired (Apr) and Aaligned (Aal) spermatogonia and the other A spermatogonia as they appear in tubules mounted in toto. This technique enabled Ais, Apr and Aal spermatogonia to be counted.Our results complete the evidence for the concept of a population of morphologically undifferentiated A spermatogonia preceding the A1 spermatogonia in the line of spermatogenesis and that among these A spermatogonia, the Ais cells are to be regarded as the stem cells of spermatogenesis.In population of Ais, Apr and Aal spermatogonia divisions take place during the life spans of A2, A4 and In spermatogonia and also rarely during the life span of B spermatogonia. During the life spans of In and B spermatogonia the Aal gradually differentiate into A1 spermatogonia. About 10% of the total number of A spermatogonia in stages 7–8, mainly Aisolated and some Apaired, do not differentiate but start a new multiplication cycle.

The spermatogonial stem cell population in adult rats. I. Their morphology, proliferation and maturation

AbstractWhole mounted segments of seminiferous tubules from rat testes have been used to investigate the morphology and proliferative activity of the undifferentiated type A spermatogonial population. This has led to the formulation of a new model for spermatogonial stem cell renewal. Three groups of undifferentiated A spermatogonia were classified according to their topographical arrangements as isolated, paired, and aligned spermatogonia. It was proposed that the isolated (as well as a few paired) spermatogonia, which were always present throughout the seminiferous epithelium, are the functional stem cells and should therefore be designated as As. Through sporadic divisions, the As spermatogonia both maintain their own numbers and give rise to pairs of cells which are destined to eventually differentiate. The latter undergo several synchronous divisions in succession, thereby forming increasingly longer chains of aligned spermatogonia. The proliferation of these chains, primarily in stages I–V, leads to a gradual expansion in the size of the undifferentiated type A population. When the population attains its maximal size in stage V, mitotic activity among the aligned cells ceases, and all of these cells morphologically transform without further division into typical A1 spermatogonia. Subsequently, the cohort of A1 cells synchronously divides in stage IX to begin the long process of spermatogonial maturation. The isolated (and a few paired) cells, which do not undergo this transformation and remain quiescent during the stage IX peak of mitosis, form a residual stock of stem cells, that, during the course of another cycle, rebuild the population of aligned A spermatogonia. In this way, a continual supply of type A1 spermatogonia which will cyclically differentiate is insured.

A new concept of spermatogonial stem-cell renewal in the mouse and its relationship to genetic effects

The stem cell of the seminiferous epithelium, designated spermatogonia A s, is radiation resistant, has a long cell cycle time, and occurs as single, isolated cells. Renewal occurs by division to form more singles; formation of a “pair” of cells constitutes the initial step in differentiation. This model differs from previous ones in that spermatogonial types with high sensitivity to cell killing do not contribute to the stem-cell pool, and owing to their transient nature, are relatively unimportant in overall genetic effects in spermatogonia. Only A s spermatogonia survived single radiation dose of 150, 500, 1000, and a fractionated 1000 R exposure. A combination of [ 3H]thymidine injection and irradiation showed equal spermatgonial labeling 8.5 and 17 days after 100 and 500 R, a decrease in percentage of labeled cells after 1000 R, and the highest value after 1000 R given as two 500 R fractions 24 h apart. These results suggest that differential cell survival may be a factor in observed mutation frequencies. The high percentage of labeled spermatogonia after 1000 R given in two 500 R fractions 24 hours apart suggests that selective action of the second exposure is an important factor in the enhanced mutation frequency observed after this treatment. The data also suggest that the spermatogonial population surviving 100 and 500 R is qualitatively similar, and that the kinetics of these cells is the same as that of A s cells in controls. Thus extrapolation of the linear portion of the mutation rate curve would not be expected to underestimate the effect of low doses.

Further evidence for the proposed way of spermatogonial stem cell renewal in the rat and the mouse.

By means of 3H-thymidine and autoradiography it could be established that in rats and mice the A1, A2 and A3 spermatogonia do not give rise to a significant number of stem cells.

Spermatogonial stem cell renewal in the rat, mouse and golden hamster. A study with the alkylating agent myleran.

With the help of the alkylating agent Myleran we confirmed our finiding that in the rat, mouse and golden hamster the spermatogonial stem cells are daughter cells of the last generation of A spermatogonia.

Spermatogonial stemcell renewal in rats and mice

By means of an autoradiographic method we verified the moment of stemcell renewal proposed by different authors for rats and mice. We found that in rats and mice the stemcells arise as daughter cells of the A4 spermatogonia.

Renewal of spermatogonia in man.

AbstractThe spermatogonia of normal adult human testis were investigated in view of clarifying their mode of proliferation and renewal. Three main types of spermatogonia were identified: the dark type A spermatogonia (Ad) tentatively considered as the stem cells, the pale type A spermatogonia (Ap) and the type B spermatogonia (B), these being the more and more differentiated elements giving rise to preleptotene spermatocytes. The dark and pale type A spermatogonia were present in all stages of the cycle of the seminiferous epithelium, the type B spermatogonia were found in stages VI, I and II of the cycle and the preleptotene spermatocytes in stages III and IV of the cycle. The type A spermatogonia divided preferentially in stage V of the cycle and the type B spermatogonia in stage II of the cycle.Quantitative data on spermatogonia and preleptotene spermatocytes revealed that the cell ratio Ad: Ap: B: Pl was equal to 1:1:2:4. This indicated that the spermatogonial stem cells divided to produce equal numbers of new stem cells (Ad) and of the more differentiated pale type A spermatogonia (Ap). Each one of the latter gave rise to two type B spermatogonia which in turn produced four spermatocytes.The arrangement in pairs of the dark and pale type A spermatogonia throughout the duration of the cycle indicated that the mitoses of spermatogonial stem cells are “equivalent” in nature; therefore, the possibility of having “differential” mitoses to explain the renewal of spermatogonial stem cells should be abandoned. Lastly, the frequent arrangement of the two classes of type A spermatogonia in homogeneous clusters indicated that the impetus which facilitates the differentiation of stem cells into the more differentiated elements (Ap) may affect homogeneous and compact groups of stem cells.