体外培养条件下SCF、LIF与bFGF对昆明白小鼠精原干细胞增殖的影响

生长因子作为细胞体外培养和在体细胞生长及增殖必需的调节因子 ,一直被广泛的关注。业已证明干细胞因子(ＳｔｅｍＣｅｌｌＦａｃｔｏｒ,ＳＣＦ)、白血病抑制因子 (ｌｅｕｋａｅｍｉａｉｎｈｉｂｉｔｏｒｙｆａｃｔｏｒ,ＬＩＦ)和碱性成纤维细胞生长因子 (ＢｓａｉｃＦｉｂｒｏｂｌａｓｔＧｒｏｗｔｈＦａｃｔｏｒ,ｂＦＧＦ)具有刺激细胞增殖的作用[1～ 4] ,但大都是对单一因子进行研究。本实验探讨用这三种生长因子的不同组合观察对小鼠精原干细胞增殖的作用 ,以期定性和定量的探讨出体外培养初期三种因子对小鼠精原干细胞生长的影响 ,为小…     

Proliferation and differentiation of bovine type A spermatogonia during long-term culture

The present study was aimed at developing a method for long-term culture of bovine type A spermatogonia. Testes from 5-mo-old calves were used, and pure populations of type A spermatogonia were isolated. Cells were cultured in minimal essential medium (MEM) or KSOM (potassium-rich medium prepared according to the simplex optimization method) and different concentrations of fetal calf serum (FCS) for 2-4 wk at 32 degrees C or 37 degrees C. Culture in MEM resulted in more viable cells and more proliferation than culture in KSOM, and better results were obtained at 37 degrees C than at 32 degrees C. After 1 wk of culture in the absence of serum, only 20% of the cells were alive. However, in the presence of 2.5% FCS, approximately 80% of cells were alive and proliferating. Higher concentrations of FCS only enhanced numbers of somatic cells. In long-term culture, spermatogonia continued to proliferate, and eventually, type A spermatogonial colonies were formed. The majority of colonies consisted mostly of groups of cells connected by intercellular bridges. Most of the cells in these colonies underwent differentiation because they were c-kit positive, and ultimately, cells with morphological and molecular characteristics of spermatocytes and spermatids were formed. Occasionally, large round colonies consisting of single, c-kit-negative, type A spermatogonia (presumably spermatogonial stem cells) were observed. For the first time to our knowledge, a method has been developed to allow proliferation and differentiation of highly purified type A spermatogonia, including spermatogonial stem cells during long-term culture.     

Proliferation and differentiation of spermatogonial stem cells in the w/wv mutant mouse testis

Mutations in the dominant-white spotting (W; c-kit) and stem cell factor (Sl; SCF) genes, which encode the transmembrane tyrosine kinase receptor and its ligand, respectively, affect both the proliferation and differentiation of many types of stem cells. Almost all homozygous W or Sl mutant mice are sterile because of the lack of differentiated germ cells or spermatogonial stem cells. To characterize spermatogenesis in c-kit/SCF mutants and to understand the role of c-kit signal transduction in spermatogonial stem cells, the existence, proliferation, and differentiation of spermatogonia were examined in the W/Wv mutant mouse testis. In the present study, some of the W/Wv mutant testes completely lacked spermatogonia, and many of the remaining testes contained only a few spermatogonia. Examination of the proliferative activity of the W/Wv mutant spermatogonia by transplantation of enhanced green fluorescent protein (eGFP)-labeled W/Wv spermatogonia into the seminiferous tubules of normal SCF (W/Wv) or SCF mutant (Sl/Sld) mice demonstrated that the W/Wv spermatogonia had the ability to settle and proliferate, but not to differentiate, in the recipient seminiferous tubules. Although the germ cells in the adult W/Wv testis were c-kit-receptor protein-negative undifferentiated type A spermatogonia, the juvenile germ cells were able to differentiate into spermatogonia that expressed the c-kit-receptor protein. Furthermore, differentiated germ cells with the c-kit-receptor protein on the cell surface could be induced by GnRH antagonist treatment, even in the adult W/Wv testis. These results indicate that all the spermatogonial stem cell characteristics of settlement, proliferation, and differentiation can be demonstrated without stimulating the c-kit-receptor signal. The c-kit/SCF signal transduction system appears to be necessary for the maintenance and proliferation of differentiated c-kit receptor-positive spermatogonia but not for the initial step of spermatogonial cell differentiation.     

Increment of murine spermatogonial cell number by gonadotropin-releasing hormone analogue is independent of stem cell factor c-kit signal

Recent studies have demonstrated that GnRH-analogues can stimulate regeneration of spermatogenesis of rats when administered after testicular damages. Although the mechanism of this phenomenon has not been elucidated yet, stem cell factor (SCF) produced by Sertoli cells was proposed to mediate the effects of GnRH-analogues on spermatogonial proliferation and/or survival. In the present study, we quantitatively evaluated the proliferation of spermatogonia and addressed whether SCF mediates the effect of GnRH-analogue on spermatogonial proliferation, using a novel approach combining spermatogonial transplantation and laser confocal microscopic observation. In the first experiment, using wild-type mice as recipients for spermatogonial transplantation, the number of donor spermatogonia per 100 Sertoli cells in each spermatogenic colony was significantly higher in the experimental group of mice treated with leuprorelin, a GnRH-agonist, than that of the control group at 4 and 5 wk after transplantation. In the second experiment, Steel/Steeldickie (Sl/Sld) mutant mice, which lack expression of membrane bound form SCF, were used as recipients. As seen in the first experiment, the number of undifferentiated spermatogonia was significantly higher in leuprorelin-treated than in the control group. Since undifferentiated spermatogonia do not express the receptor of SCF, the present study clearly demonstrates that neither membrane-bound nor secreted forms of SCF are involved in the mechanism of GnRH-analogue's effect on spermatogonial proliferation and/or survival.     

Basic features of bovine spermatogonial culture and effects of glial cell line-derived neurotrophic factor

Spermatogonial stem cells (SSC) are a small self-renewing subpopulation of type A spermatogonia, which for the rest are composed of differentiating cells with a very similar morphology. We studied the development of primary co-cultures of prepubertal bovine Sertoli cells and A spermatogonia and the effect of glial cell line-derived neurotropic factor (GDNF) on the numbers and types of spermatogonia, the formation of spermatogonial colonies and the capacity of the cultured SSC to colonize a recipient mouse testis. During the first week of culture many, probably differentiating, A spermatogonia entered apoptosis while others formed pairs and chains of A spermatogonia. After 1 week colonies started to appear that increased in size with time. Numbers of single (A(s)) and paired (A(pr)) spermatogonia were significantly higher in GDNF treated cultures at Days 15 and 25 (P < 0.01 and 0.05, respectively), and the ratio of A(s) to A(pr) and spermatogonial chains (A(al)) was also higher indicating enhanced self-renewal of the SSC. Furthermore, spermatogonial outgrowths in the periphery of the colonies showed a significantly higher number of A spermatogonia with a more primitive morphology under the influence of GDNF (P < 0.05). Spermatogonial stem cell transplantation experiments revealed a 2-fold increase in stem cell activity in GDNF treated spermatogonial cultures (P < 0.01). We conclude that GDNF rather than inducing proliferation, enhances self-renewal and increases survival rates of SSC in the bovine spermatogonial culture system.     

Apoptosis,onset and maintenance of spermatogenesis: evidence for the involvement of Kit in Kit-haplodeficient mice

Kit/stem cell factor (SCF ) has been reported to be involved in survival and proliferation of male differentiating spermatogonial cells. This kinetics study was designed to assess the role of Kit/SCF during spermatogenesis in mice, and the extent of male programmed germ cell death was measured between 8 and 150 days of age. For this purpose, 129/Sv inbred mice in which one Kit allele was inactivated by an nlslacZ sequence insertion (Kit(W-lacZ/+)) were compared with 129/Sv inbred mice with wild-type alleles at the Kit locus. Four different approaches were used: 1) morphometric study to assess spermatogenesis, 2) flow cytometry to study testicular cell ploidy, 3) in situ end labeling to detect apoptosis, and 4) follow-up of reporter gene expression. Spermatogenesis was lower in Kit(W-lacZ/+) heterozygous mice both at the onset of spermatogenesis and during adulthood. Indeed, greater apoptosis occurred at the onset of spermatogenesis. This was followed in the adult by a smaller seminiferous tubule diameter and a lower ratio between type B spermatogonia and type A stem spermatogonia in Kit(W-lacZ/+) mice compared with Kit(+/+) mice. These differences are probably related to the Kit haplodeficiency, which was the only difference between the two genotypes. Germ cell counts and testicular cell ploidy revealed delayed meiosis in Kit(W-lacZ/+) mice. Reporter gene expression confirmed expression of the Kit gene at the spermatogonial stage and also revealed Kit expression during the late pachytene/diplotene transition. These results suggest involvement of Kit/SCF at different stages of spermatogenesis.     

卵泡刺激素和表皮生长因子对小鼠精原细胞增殖的影响

利用生殖细胞-体细胞体外无血清共培养模型研究了卵泡刺激素(FSH)和表皮生长因子(EGF)对小鼠A型精原细胞增殖的影响。精原细胞在ITS培养液(添加胰岛素、转铁蛋白和亚硒酸钠的DMEM)中培养24h后进行c-kit免疫细胞化学鉴定和EGF及其受体(EGFR)免疫细胞化学检测,72h后测定其形成集落数的情况。结果表明:ITS培养液能维持生殖细胞的活性,增殖细胞核抗原(PCNA)的表达增高。A型精原细胞呈c-kit阳性,EGF和EGFR主要表达于精原细胞。单独的FSH(1～100ng/ml)或EGF(1～10ng/ml)显著促进精原细胞集落数的增加。此外,EGF(0.1ng/ml)联合FSH(10ng/ml)具有加性效应,但更高剂量的EGF(1～10ng/ml)则降低了FSH的刺激作用。结果说明FSH可联合适量的EGF促进精原细胞的增殖。     

Human recombinant stem cell factor promotes spermatogonial proliferation,but not meiosis initiation in organ culture of newt testis fragments

We previously showed that mammalian FSH stimulates the proliferation of newt spermatogonia and induces their differentiation into primary spermatocytes in vitro. In the current study, to examine a possibility that stem cell factor (SCF) is involved in the proliferation of newt spermatogonia and/or their differentiation into primary spermatocytes, human recombinant SCF (rhSCF) was added to organ culture of testicular fragments. rhSCF was found to stimulate the spermatogonial proliferation and the spermatogonia progressed to the seventh generation that is the penultimate stage before primary spermatocyte stage. However, the spermatogonia did not differentiate into primary spermatocytes, but instead died of apoptosis. These results indicate that rhSCF promotes the proliferation of newt spermatogonia, but not the initiation of meiosis.     

性成熟前食蟹猴生精细胞的发育进程

目的阐明性成熟前食蟹猴生精细胞的发育进程。方法分别采集性成熟前不同年龄（0岁、0.5岁、1岁、1.5岁、2岁、2.5岁、3岁、3.5岁、4岁）食蟹猴睾丸,制作石蜡切片,进行HE染色和PAS/H染色。根据生精细胞的染色特性,分析性成熟前食蟹猴生精细胞的发育进程,并对食蟹猴精原干细胞进行初步鉴定。结果 HE染色结果显示,1岁及以下食蟹猴生精上皮上生精细胞仅有精原干细胞（包括Ad、At及Ap型精原细胞）,1.5岁食蟹猴生精上皮上开始出现B型精原细胞,3岁食蟹猴生精上皮上出现精母细胞,4岁食蟹猴生精上皮上出现从精原干细胞到精子的所有生殖细胞。PAS/H染色结果显示,1～2.5岁食蟹猴Ad型精原细胞胞质呈PAS阳性,At型精原细胞胞质呈PAS弱阳性,Ap型精原细胞胞质呈PAS阴性;其他生精细胞及支持细胞胞质呈阴性;0.5岁及以下,3岁及以上食蟹猴生精细胞的胞质PAS/H染色特性与前者存在差异。结论本文详细阐述了性成熟前食蟹猴生精细胞随年龄增长的渐次性发育模式,并建立了性成熟前食蟹猴精原干细胞原位鉴定的一种新方法,这些研究结果为食蟹猴精原干细胞的其他相关研究奠定了基础。     

Recombinant human insulin-like growth factor I stimulates all stages of 11-ketotestosterone-induced spermatogenesis in the Japanese eel, Anguilla japonica, in vitro.

In this study, we examined the in vitro effects of insulin-like growth factor I (IGF-I) in the presence or absence of 11-ketotestosterone (11-KT: the spermatogenesis-inducing hormone) on the proliferation of Japanese eel (Anguilla japonica) testicular germ cells. Initially, a short-term culture (15 days) of testicular tissue with only type A and early type B spermatogonia (preproliferated spermatogonia) was carried out in Leibovitz-15 growth medium supplemented with different concentrations of recombinant human IGF (rhIGF)-I or -II in the presence or absence of 10 ng/ml of 11-KT. Late type B spermatogonia (proliferated spermatogonia) were observed in treatments of 100 ng/ml of both rhIGF-I and -II in combination with 11-KT, indicating the onset and progression of spermatogenesis. In all tested rhIGF-I concentrations (except 0.1 ng/ml) supplemented with 11-KT, late type B spermatogonia were detected in at least one individual. Then, we proceeded with an in vitro 45-day culture of testicular tissue with 100 ng/ml of rhIGF-I in the presence or absence of 10 ng/ml of 11-KT to test the long-term effects of rhIGF-I on the spermatogenetic cycle. The presence of all types of germ cells, including spermatozoa, in the testis cultured with the admixture of the two hormones indicated that the germ cells underwent complete spermatogenesis whereas no germ cell proliferation was observed when the rhIGF-I was applied alone. These results suggest that IGF-I in the presence of 11-KT plays an essential role in the onset, progress, and regulation of spermatogenesis in the testis of the Japanese eel.     

Morphological characteristics of the spermatogonial stem cells in man

The present investigation is concerned with establishing morphological criteria of spermatogonial stem cells in man. Testicular biopsies from patients having undergone semicastration for malignant tumors and radio- and chemotherapy for one year following the operation were studied light and electron microscopically. Those spermatogonial types that survived the treatment were regarded as stem cells in view of the fact that the stem cells, in contrast to the more differentiated spermatogonia, are radiation resistant and less sensitive to various noxious agents. In 7 out of 28 cases examined, a small number of spermatogonia was found adjacent to the basement membrane. The majority of these cells show the characteristic features of pale type A spermatogonia, while a few cells may represent variants of this cell type. The dark type A spermatogonia are almost completely eliminated from the seminiferous tubules. A concept is proposed that the stem cells of the human testis may be derived from the pale type A spermatogonia or the variants of this cell type.     

Paracrine effects of oocyte secreted factors and stem cell factor on porcine granulosa and theca cells <Emphasis Type="Italic">in vitro</Emphasis>

Oocyte control of granulosa and theca cell function may be mediated by several growth factors via a local feedback loop(s) between these cell types. This study examined both the role of oocyte-secreted factors on granulosa and thecal cells, cultured independently and in co-culture, and the effect of stem cell factor (SCF); a granulosa cell derived peptide that appears to have multiple roles in follicle development. Granulosa and theca cells were isolated from 2–6 mm healthy follicles of mature porcine ovaries and cultured under serum-free conditions, supplemented with: 100 ng/ml LR3 IGF-1, 10 ng/ml insulin, 100 ng/ml testosterone, 0–10 ng/ml SCF, 1 ng/ml FSH (granulosa), 0.01 ng/ml LH (theca) or 1 ng/ml FSH and 0.01 ng/ml LH (co-culture) and with/without oocyte conditioned medium (OCM) or 5 oocytes. Cells were cultured in 96 well plates for 144 h, after which viable cell numbers were determined. Medium was replaced every 48 h and spent medium analysed for steroids.     

Synergism between stem cell factor and granulocyte-macrophage colony-stimulating factor on cell proliferation by induction of cyclins

Synergism between stem cell factor (SCF) and granulocyte-macrophage colony-stimulating factor (GM-CSF) has been shown to be essential for hematopoietic cell proliferation. Since HML-2 cells proliferate exponentially in the presence of SCF and GM-CSF together, we analyzed the molecular mechanism of the interaction between these two factors in the cells. An immediate-early gene product, c-myc, was additively upregulated in HML-2 cells by addition of a combination of SCF and GM-CSF. c-myc antisense oligonucleotides effectively suppressed cell proliferation and downregulated the induction of D3, E, A, and B cyclins in HML-2 cells stimulated with the two-factor combination. HML-2 cells arrested at the G0/G1 phase with SCF alone and expressed modest amounts of c-myc and cyclin D3, but not cyclin E. With GM-CSF treatment alone, the cells could not progress to the G2/M phase and expressed c-myc, cyclin D3 and cyclin E but not cyclins A or B. The addition of the counterpart cytokine resulted in cell cycle completion by induction of the deficient cyclins. Taken together, it appears that the induction of c-myc is an indispensable event in the proliferation of HML-2 cells and that the cytokines SCF and GM-CSF interact reciprocally for expression of all cyclins required for cell cycle progression.     

Gfra1 silencing in mouse spermatogonial stem cells results in their differentiation via the inactivation of RET tyrosine kinase

Spermatogenesis is the process by which spermatogonial stem cells divide and differentiate into sperm. The role of growth factor receptors in regulating self-renewal and differentiation of spermatogonial stem cells remains largely unclear. This study was designed to examine Gfra1 receptor expression in immature and adult mouse testes and determine the effects of Gfra1 knockdown on the proliferation and differentiation of type A spermatogonia. We demonstrated that GFRA1 was expressed in a subpopulation of spermatogonia in immature and adult mice. Neither Gfra1 mRNA nor GFRA1 protein was detected in pachytene spermatocytes and round spermatids. GFRA1 and POU5F1 (also known as OCT4), a marker for spermatogonial stem cells, were co-expressed in a subpopulation of type A spermatogonia from 6-day-old mice. In addition, the spermatogonia expressing GFRA1 exhibited a potential for proliferation and the ability to form colonies in culture, which is a characteristic of stem cells. RNA interference assays showed that Gfra1 small interfering RNAs (siRNAs) knocked down the expression of Gfra1 mRNA and GFRA1 protein in type A spermatogonia. Notably, the reduction of Gfra1 expression by Gfra1 siRNAs induced a phenotypic differentiation, as evidenced by the elevated expression of KIT, as well as the decreased expression of POU5F1 and proliferating cell nuclear antigen (PCNA). Furthermore, Gfra1 silencing resulted in a decrease in RET phosphorylation. Taken together, these data indicate that Gfra1 is expressed dominantly in mouse spermatogonial stem cells and that Gfra1 knockdown leads to their differentiation via the inactivation of RET tyrosine kinase, suggesting an essential role for Gfra1 in spermatogonial stem cell regulation.     

Morphology and cell population kinetics of primary spermatogonia in the frog (Rana esculenta) (Amphibia: Anura)

Two morphologically distinct primary spermatogonial cell types were observed in the frog testis and distinguished on the basis of nuclear characteristics. They have been designated the pale and dark types of primary spermatogonia. On the basis of a kinetic analysis, it is proposed that the pale spermatogonia possess the faculty of self-renewal as well as that of forming dark spermatogonia; they are thus bipotential stem cells comparable to the undifferentiated type of mammalian spermatogonia. The dark spermatogonia, in contrast, are committed to a single pathway, i.e. to form secondary sperrnatogonia, and can be defined as differentiated or committed elements of the primary spermatogonial population. The number of stem cell spermatogonia and differentiated spermatogonia vary according to the period of the year, as does the rate of turnover of stem cells, with nearly 60–90% of cells temporarily out of the cell cycle at any given time. It is indicated that the spermatogonial population represents a 'cell renewal system' in a steady state for appreciably long periods of time, however, changing with season in as far as the magnitude of yield of spermatogonial cells is concerned. This implies that an equality should exist between the rate at which stem cells enter cell-cycling and the rate at which daughter cells change their morphological identity.     

A critical stage in spermatogenesis for radiation-induced cell death in the medaka fish, Oryzias latipes

To ensure the high-fidelity transmission by reproductive cells of genetic information from generation to generation, cells have evolved surveillance systems to eliminate genomic lesions by inducing cell suicide and/or DNA repair. In this report, gamma-ray-induced cell death was investigated using the medaka fish, Oryzias latipes, because of the ease with which the differentiation stages of its spermatogenic cells can be identified. After 4.75 Gy gamma irradiation, the maximum rate of death of spermatogonial stem cells was observed at 18 h, and that of differentiating spermatogonia was at 12 h, followed by a peak in the extent of DNA fragmentation detected by the TUNEL assay. Dose-response curves for the death rate showed an obvious increase in the death rate for early-differentiating spermatogonia even after 0.11 Gy irradiation, whereas there were no such increases for spermatogonial stem cells and late-differentiating spermatogonia. In the male germ cells of this fish, the stage during spermatogenesis most sensitive to radiation-induced cell death is in early-differentiating spermatogonia, the immediate descendants of the stem cells. These spermatogonia may have a rigorous surveillance system for genomic lesions induced in spermatogonial stem cells.     

Regulation of proliferation and differentiation in spermatogonial stem cells: the role of c-kit and its ligand SCF

To study self-renewal and differentiation of spermatogonial stem cells, we have transplanted undifferentiated testicular germ cells of the GFP transgenic mice into seminiferous tubules of mutant mice with male sterility, such as those dysfunctioned at Steel (Sl) locus encoding the c-kit ligand or Dominant white spotting (W) locus encoding the receptor c-kit. In the seminiferous tubules of Sl/Sl(d) or Sl(17H)/Sl(17H) mice, transplanted donor germ cells proliferated and formed colonies of undifferentiated c-kit (-) spermatogonia, but were unable to differentiate further. However, these undifferentiated but proliferating spermatogonia, retransplanted into Sl (+) seminiferous tubules of W mutant, resumed differentiation, indicating that the transplanted donor germ cells contained spermatogonial stem cells and that stimulation of c-kit receptor by its ligand was necessary for maintenance of differentiated type A spermatogonia but not for proliferation of undifferentiated type A spermatogonia. Furthermore, we have demonstrated that their transplantation efficiency in the seminiferous tubules of Sl(17H)/Sl(17H) mice depended upon the stem cell niche on the basement membrane of the recipient seminiferous tubules and was increased by elimination of the endogenous spermatogonia of mutant mice from the niche by treating them with busulfan.     

Secretion of stem cell factor and granulocyte-macrophage colony-stimulating factor by mouse embryos in culture: influence of group culture

Previous studies showed that the addition of a growth factor to the culture medium could modulate embryo development. The possible secretion of different factors to the culture medium by the embryo itself, however, has been poorly evaluated. The present study was designed to investigate: (1) the influence of single or group culture on the development of 2-cell mouse embryos (strain CD-1) to the blastocyst stage; (2) the release of granulocyte-macrophage colony-stimulating factor (GM-CSF) and stem cell factor (SCF) into the culture medium by the embryo; and (3) the levels of GM-CSF and SCF in the culture medium from both single and group embryos. Two-cell CD-1 mouse embryos were cultured for 96 h singly or in groups of five embryos per drop. GM-CSF and SCF were assayed by ELISA in the complete culture medium. It was found that embryos cultured in groups gave a higher percentage of total blastocyst formation and hatched blastocyst when compared with single embryo culture. The mouse embryos secreted GM-CSF and SCF to the culture medium. The concentration of these cytokines is significantly higher in the group cultures than the level found in single cultures. In conclusion, mouse embryos in culture secrete GM-CSF and SCF to the culture medium and the concentration of these cytokines increases during communal culture. These factors may be operating in both autocrine and paracrine pathways to modulate embryo development during in vitro culture.     

Spermatogenetic clones developing from repopulating stem cells surviving a high dose of an alkylating agent.

We investigated stem cell renewal and differentiation in 10- and 15-days-old spermatogonial clones developing in mouse seminiferous epithelium after an extremely large cell loss, inflicted by high doses of the alkylating agent Myleran. The spermatogonial clones arise from cells that resemble the Ais spermatogonia but have a larger nuclear diameter. In spite of their mitotic activity these 'repopulating stem cells' lie mainly isolated or in pairs. This explained by migration and differentiation. Migration appeared to occur at random in all directions along the basement membrane of the seminiferous tubule. After one or more divisions of the stem cells, a second type of cell appears, which is called the 'differentiating spermatogomium'. The time elapsing before this type of cell appears, depends on the dose of Myleran: the larger the dose the later differentiation starts. A relation could be demonstrated between the stage of the cycle of the seminiferous epithelium and the start of differentiation. Differentiating cells were found isolated or in groups of two, four, eight or sixteen cells. Hence we concluded that at least up to their fourth division differentiating cells divide synchronously without degenerations. Three types of division of repopulating stem cells were distinguished, producing (1) two repopulating stem cells, (2) one repopulating stem cell and one cell starting spermatogonial differentiation, or (3) two differentiating cells. Type 1 divisions were found most frequently.     

GDNF对精原干细胞增殖及其分化的调控机制

阐述了胶质细胞源性神经营养因子(GDNF)及其受体与精原干细胞增殖和分化的关系。GDNF能够促进未分化的精原细胞增长,并且可以调节精原干细胞自我更新与分化的微环境,参与其分化的第一步,是精原干细胞存活的重要营养因子。