哺乳动物雌性生殖干细胞研究的质疑、进展及挑战

传统观点认为雌性哺乳动物在出生后即失去产生新生殖细胞的能力,但近年来研究人员在多种出生后的哺乳动物卵巢内成功分离并培养到一类生殖细胞,这类细胞具有自我增殖和分化成卵母细胞的能力,从而确认出生后的哺乳类动物卵巢内存在雌性生殖干细胞的事实。该文拟从雌性生殖干细胞的研究历史及发现,生殖界对雌性生殖干细胞的质疑,近年来雌性生殖干细胞的研究进展和应用,以及当前雌性生殖干细胞研究所存在的不足、所面临的机遇与挑战作一评述。     

哺乳动物出生后卵巢中卵子再发生的研究进展

关于哺乳动物出生后卵巢内是否有新的卵子继续发生或者说出生后的卵巢中是否存在生殖干细胞以维持卵子继续发生问题,一直存在争议.占主流的观点是"出生后的卵巢内卵泡不可更新"说,但仍不断有报道对此论断提出挑战.这既是个生殖生物学的重大基础理论问题,又对雌性生殖、生殖医学、生殖期的延长及干细胞研究等许多相关问题有着极大的影响和深远的意义.因此就这一争议性问题的研究进程作简要回顾.     

哺乳动物卵巢中生殖干细胞的研究历史与进展

对于出生后的哺乳动物卵巢中是否存在生殖干细胞以维持卵泡的更新一直争议不断,现就该领域的研究历史及最新进展进行综述.     

小鼠卵巢几个重要发育事件的初步研究

选定多个阶段小鼠卵巢进行切片染色和生殖细胞计数统计等分析,以发现该阶段小鼠卵巢的发育特点。结果显示在胚胎发育第12.5 d的生殖嵴中,大部分的生殖细胞正进行有丝分裂增殖,并以生殖包囊的形式存在;在出生后第2 d的小鼠卵巢中,有大量紧密接触的原始卵泡,表明生殖包囊刚完成重组形成原始卵泡;在第5 d的小鼠卵巢中,原始卵泡仍占有大部分比例,但也有大量的初级卵泡处于发育之中;在出生后第10 d的卵巢中同时有原始卵泡、初级卵泡和次级卵泡的发育;老年小鼠(16个月大)卵巢中已基本没有卵母细胞。     

雌性哺乳动物生殖干细胞：在争议中前进

100多年以来,雌性哺乳动物出生后是否存在生殖干细胞的争议尚无定论．2004年,研究人员从出生后的小鼠卵巢中发现并分离到雌性生殖干细胞(female germline stem cells,FGSCs),挑战了存在近半个世纪的理论：哺乳动物出生后不会对卵母细胞库进行更新．随后很多研究不仅指出哺乳动物出生后卵巢中新生成的卵母细胞源自FGSCs,而且发现如果将FGSCs移植回受体卵巢,它们能够产生功能性的卵母细胞并由此得到健康的后代．可是,有的研究小组重复实验或者精心设计实验,却未得到相同的结果,甚至得出相反的结果．最近,有研究者从育龄女性卵巢中分离到了在体内外都能够分化出功能性卵母细胞的FGSCs,不过这些卵母细胞的受精能力还有待证实．本文回顾了哺乳动物FGSCs的研究历程,并对这一存在已久的争论以及FGSCs研究方向和将来的运用前景展开了评述．     

卵巢相关干细胞研究进展

卵巢是由体细胞和生殖细胞构成的,其发生、发育及功能与相关干细胞的关系非常紧密,但还有很多疑问和争议,如是否存在成体卵巢生殖干细胞等。除了在正常卵巢生理功能中发挥重要作用,卵巢中的干细胞的变异也会导致卵巢肿瘤及其它功能障碍情况的发生,如多囊卵巢综合症、卵巢早衰和不孕不育等。本综述主要讨论近期有关干细胞在卵子、卵巢的发育及卵巢生理和病理情况下的作用的研究进展。     

哺乳动物卵巢卵泡发育调控机制研究进展

卵巢作为雌性哺乳动物的性腺,是由卵母细胞和不同类型的体细胞组成的异质性器官。卵巢在功能上,一方面担负了与雌性个体健康有关的内分泌调节功能,另一方面则承载了产生成熟卵母细胞并繁衍子代的重要任务。而承担上述功能的单位为卵泡,即卵母细胞和卵泡体细胞共同构成的复合体。对于具有较长生殖寿命的哺乳动物而言,卵泡在卵巢内的发育是一个内部协同与外部调控的精密有序过程。其中后期促性腺激素依赖的有腔卵泡发育直接调控生殖周期的产生,而近期越来越多的证据表明早期卵泡的有序发育与雌性生殖寿命维持密切关联。因此,卵泡在体正常发育与雌性个体的健康息息相关;而深入探索卵泡发育调控机制,可直接指导我们认识包括人类在内的雌性哺乳动物生殖寿命的维持机制,并在未来对其进行可能的调控。近年来,伴随着新技术和新方法的产生,特别是基因修饰动物的开发以及新型显微技术的出现,对卵泡发育特别是早期卵泡发育的调控机制研究有了长足的进步。本综述围绕着卵泡在体发育中的关键生理事件,将近年来对卵泡的生理发育调节机制研究进行梳理,并重点聚焦于早期卵泡发育的体内相关调控机制研究进展。     

胎猪卵巢发生过程中的组织学变化

哺乳动物胎儿在出生前, 卵巢发生经历了众多连续的组织学变化, 主要包括原生殖细胞的增殖、分化, 原始卵巢和性索形成, 卵原细胞的增殖、分化和凋亡, 以及原始卵泡的形成、发育和闭锁等.卵巢发生是生殖活动中最初的也是重要的生理事件, 认识这一过程具有特殊的意义.此前, 关于猪胎儿期卵巢发育已经有零星的报道, 但对于卵巢发生过程中的组织学变化尚缺乏连贯和系统的描述.现结合已有的研究报道, 对猪卵巢发生过程中的组织学变化进行了全面的总结, 为相关研究工作提供一定的参考.     

小鼠和人类生殖干细胞形成、特化和维持

哺乳动物胚胎植入子宫后,随着原肠运动的发生,胚胎开始向三个胚层分化,同时生殖细胞开始形成和特化。胚胎最早期的生殖细胞被称为原始生殖细胞(primordial germ cell, PGC),雌雄原始生殖细胞增殖并迁移到生殖嵴,持续增殖后分别进入减数分裂前期和有丝分裂阻滞,分化形成卵原细胞和精原干细胞,经过复杂的发育过程分化形成卵母细胞和精子。该文回顾了小鼠和人类的原始生殖细胞的形成和特化过程,并且对小鼠和人类精原干细胞的分子特征和体外培养体系进行了总结。     

禽类卵泡生殖内分泌机能及其调控

雌禽只有左侧卵巢和输卵管,而右侧卵巢和输卵管在胚胎发育过程中已逐步退化,在生殖功能上也出现了与哺乳动物不同的特征。近年来随着研究的不断深入,发现禽类卵巢卵泡内分泌有许多不同于哺乳动物的活动规律。本文主要以鸡卵泡内分泌活动方面的研究进展,对禽类卵泡在生殖内分泌活动中的作用进行探讨性的概述,并与哺乳动物作一简单比较。 一、卵泡发育过程中的形态学变化 雌禽卵巢位于身体左侧,左肾的前方,通过卵巢系膜韧带悬于腹腔的背壁上,外观象一串葡萄,含有发育不同阶段的许多卵泡。性成熟     

Role for dopamine in malonate-induced damage in vivo in striatum and in vitro in mesencephalic cultures

Defects in mitochondrial energy metabolism have been implicated in the pathology of several neurodegenerative disorders. In addition, the reactive metabolites generated from the metabolism and oxidation of the neurotransmitter dopamine (DA) are thought to contribute to the damage to neurons of the basal ganglia. We have previously demonstrated that infusions of the metabolic inhibitor malonate into the striata of mice or rats produce degeneration of DA nerve terminals. In the present studies, we demonstrate that an intrastriatal infusion of malonate induces a substantial increase in DA efflux in awake, behaving mice as measured by in vivo microdialysis. Furthermore, pretreatment of mice with tetrabenazine (TBZ) or the TBZ analogue Ro 4-1284 (Ro-4), compounds that reversibly inhibit the vesicular storage of DA, attenuates the malonate-induced DA efflux as well as the damage to DA nerve terminals. Consistent with these findings, the damage to both DA and GABA neurons in mesencephalic cultures by malonate exposure was attenuated by pretreatment with TBZ or Ro-4. Treatment with these compounds did not affect the formation of free radicals or the inhibition of oxidative phosphorylation resulting from malonate exposure alone. Our data suggest that DA plays an important role in the neurotoxicity produced by malonate. These findings provide direct evidence that inhibition of succinate dehydrogenase causes an increase in extracellular DA levels and indicate that bioenergetic defects may contribute to the pathogenesis of chronic neurodegenerative diseases through a mechanism involving DA.     

Scurvy in capybaras bred in captivity in Argentine

In order to determine if the absence of vitamin C in the diet of capybaras (Hydrochoerus hydrochaeris) causes scurvy, a group of seven young individuals were fed food pellets without ascorbic acid, while another group of eight individuals received the same food with 1 g of ascorbic acid per animal per day. Animals in the first group developed signs of scurvy-like gingivitis, breaking of the incisors and death of one animal. Clinical signs appeared between 25 and 104 days from the beginning of the trial in all individuals. Growth rates of individuals deprived of vitamin C was considerably less than those observed in the control group. Deficiency of ascorbic acid had a severe effect on reproduction of another population of captive capybaras. We found that the decrease in ascorbic acid content in the diet affected pregnancy, especially during the first stages. The results obtained suggest that it is necessary to supply a suitable quantity of vitamin C in the diet of this species in captivity.     

Changes in lactate dehydrogenase activity in chicken tissues in hyperthyreosis in ontogenesis

The lactate dehydrogenase activity in reactions of lactate oxidation and synthesis was studied in subfractions of the chicken brain, heart and liver at the embryonal, early postembryonal and adult stages of development after thyroxine administration. It has been shown that during embryogenesis thyroxine predominantly enhanced the rate of lactate oxidation in the mitochondrial tissues. A marked increase in the lactate synthesis was found in cytoplasm of the adult chicken tissues. Specificity of enzyme activity alterations was detected in the chicken brain during ontogenesis after thyroxine administration.     

SSTR5 ablation in islet results in alterations in glucose homeostasis in mice

Somatostatin (SST) peptide is a potent inhibitor of insulin secretion and its effect is mediated via somatostatin receptor 5 (SSTR5) in the endocrine pancreas. To investigate the consequences of gene ablation of SSTR5 in the mouse pancreas, we have generated a mouse model in which the SSTR5 gene was specifically knocked down in the pancreatic beta cells (betaSSTR5Kd) using the Cre-lox system. Immunohistochemistry analysis showed that SSTR5 gene expression was absent in beta cells at three months of age. At the time of gene ablation, betaSSTR5Kd mice demonstrated glucose intolerance with lack of insulin response and significantly reduced serum insulin levels. Insulin tolerance test demonstrated a significant increase of insulin clearance in vivo at the same age. In vitro studies demonstrated an absence of response to SST-28 stimulation in the betaSSTR5Kd mouse islet, which was associated with a significantly reduced SST expression level in betaSSTR5Kd mice pancreata. In addition, betaSSTR5Kd mice had significantly reduced serum glucose levels and increased serum insulin levels at 12 months of age. Glucose tolerance test at an older age also indicated a persistently higher insulin level in betaSSTR5Kd mice. Further studies of betaSSTR5Kd mice had revealed elevated serum C-peptide levels at both 3 and 12 months of age, suggesting that these mice are capable of producing and releasing insulin to the periphery. These results support the hypothesis that SSTR5 plays a pivotal role in the regulation of insulin secretion in the mouse pancreas.