高國龍
摘要:卵巢因子對卵母細(xì)胞發(fā)育的影響已成為發(fā)育生物學(xué)研究的主要內(nèi)容,卵巢產(chǎn)生的大量生長因子通過自分泌/旁分泌方式對生發(fā)泡破裂(Germinal Vesicle Breakdown,GVBD)、第一極體釋放、胚胎發(fā)生及早期胚胎發(fā)育發(fā)揮調(diào)控作用。對卵巢因子調(diào)控作用的深入研究有助于進(jìn)一步了解卵母細(xì)胞成熟及早期胚胎發(fā)育過程中的細(xì)胞通訊系統(tǒng)網(wǎng),尋找治療不孕不育的新途徑和新方法,為體外成熟、體外受精及胚胎干細(xì)胞分化制定更加優(yōu)化的培養(yǎng)環(huán)境。概述了目前卵巢因子在小鼠卵母細(xì)胞發(fā)育調(diào)控中的研究進(jìn)展。
關(guān)鍵詞:小鼠;卵巢因子;卵母細(xì)胞;胚胎;發(fā)育
中圖分類號(hào):S811文獻(xiàn)標(biāo)識(shí)碼:A文章編號(hào):0439-8114(2012)06-1085-04
The Effects of Ovarian Factor on the Development of Mouse Oocytes
GAO Guo-long
(College of Life Science, Guizhou Normal University, Guiyang 550001,China)
Abstract: The study on the effects of ovarian factors on the development of oocytes had become the main content of developmental biology, ovarian production of growth factors further act as paracrine and/or autocrine factors during GVBD, extrusion of the first polar body, early embryogenesis and early embryonic development. Studies on ovarian factors contribute to further understanding of intercellular communication networks in the development of oocytes and early embryos, and these networks could lead to new approaches in the treatment of infertility, and facilitate future formulation for the optimal culture conditions for in vitro maturation, in vitro fertilization and embryonic stem cell derivation. Progress of ovarian factors in mouse oocytes development was summarized.
Key words: mouse; ovarian factor; oocytes; embryos; development
隨著人類不孕不育及動(dòng)物胚胎工程領(lǐng)域體外受精和體細(xì)胞克隆技術(shù)研究的逐漸深入,卵母細(xì)胞發(fā)育機(jī)制已經(jīng)成為發(fā)育生物學(xué)研究的重要內(nèi)容之一[1,2],人們通過對細(xì)胞間通訊系統(tǒng)的研究來提高卵母細(xì)胞的發(fā)育潛能[3-6]。
大量的研究證實(shí),內(nèi)分泌激素可以刺激卵巢產(chǎn)生大量的生長因子,促使卵母細(xì)胞成熟及發(fā)育,顆粒細(xì)胞和卵母細(xì)胞也可以產(chǎn)生類似卵巢因子的生長因子促使卵母細(xì)胞進(jìn)一步發(fā)育[4,5],現(xiàn)在卵巢因子對卵母細(xì)胞發(fā)育的影響已成為發(fā)育生物學(xué)研究的主要內(nèi)容。本文就目前小鼠卵母細(xì)胞發(fā)育過程中發(fā)現(xiàn)的卵巢因子的種類、對卵母細(xì)胞發(fā)育的影響作用、調(diào)控方式及所用到的研究方法等綜述如下。
1卵巢因子的發(fā)現(xiàn)及其作用
在哺乳動(dòng)物中,發(fā)育卵泡中的初級卵母細(xì)胞被阻滯在第一次減數(shù)分裂前期的雙線期,卵母細(xì)胞處于該階段長達(dá)數(shù)月甚至數(shù)年。隨著排卵前內(nèi)分泌激素分泌水平的逐漸提高,卵母細(xì)胞繼續(xù)減數(shù)分裂,進(jìn)而表現(xiàn)出生發(fā)泡破裂(Germinal vesicle breakdown,GVBD)、染色質(zhì)濃縮及第一極體釋放等有助于受精和早期胚胎發(fā)育的特征。GVBD和第一極體釋放是卵母細(xì)胞核成熟的標(biāo)志,除此之外,卵母細(xì)胞也需要細(xì)胞質(zhì)組分的變化來實(shí)現(xiàn)胞質(zhì)成熟,才有利于隨后的胚胎發(fā)生,并為植入前胚胎的發(fā)育做好準(zhǔn)備[7,8]。
雖然排卵前的促黃體素(Luteinizing hormone, LH)對卵母細(xì)胞成熟起最重要和最直接的作用,但由于生殖細(xì)胞缺乏LH受體,LH和人絨毛膜促性腺激素(Human chorionic gonadotropin,HCG)等并沒有直接作用于卵母細(xì)胞。LH/HCG對卵母細(xì)胞的調(diào)節(jié)功能可能是通過對LH敏感的體細(xì)胞的旁分泌因子來調(diào)控,或者是將卵丘細(xì)胞或顆粒細(xì)胞產(chǎn)生的細(xì)胞信號(hào)通過細(xì)胞間的緊密連接向卵母細(xì)胞傳遞來完成[9]。后來的研究證實(shí),內(nèi)分泌激素LH刺激卵巢產(chǎn)生大量卵巢因子,以促進(jìn)GVBD的發(fā)生,而顆粒細(xì)胞和卵丘細(xì)胞也可以產(chǎn)生相似的生長因子[4,5],這些因子有利于卵母細(xì)胞受精及植入前胚胎的繼續(xù)發(fā)育。同時(shí),早期胚胎發(fā)育過程也包括機(jī)體通過自分泌/旁分泌途徑產(chǎn)生的大量生長因子和細(xì)胞因子的參與[3,10]。
通過對特定基因及其表達(dá)蛋白的檢測分析,人們不但在卵巢、顆粒細(xì)胞、卵丘細(xì)胞和卵母細(xì)胞中檢測到卵巢因子的表達(dá),而且在妊娠動(dòng)物的輸卵管和子宮組織中也檢測到卵巢因子及其受體蛋白的表達(dá)。卵巢因子不但促使GVBD和第一極體釋放,進(jìn)而完成卵母細(xì)胞核成熟,還有可能通過自分泌/旁分泌對胚胎發(fā)生及早期胚胎發(fā)育產(chǎn)生調(diào)控作用。進(jìn)一步研究卵巢因子在卵母細(xì)胞發(fā)育中的調(diào)控作用有助于了解卵母細(xì)胞成熟及早期胚胎發(fā)育過程中的細(xì)胞通訊系統(tǒng)網(wǎng),尋找治療不孕不育的新途徑和新方法,為體外成熟、體外受精及早期胚胎發(fā)育制定更加優(yōu)化的培養(yǎng)環(huán)境。
2主要卵巢因子
2.1BDNF
BDNF(Brain-derived neurotrophic factor)最初是從豬腦純化的小分子堿性蛋白質(zhì),是一種腦源性神經(jīng)營養(yǎng)因子,其對神經(jīng)細(xì)胞的生長發(fā)育及保護(hù)修復(fù)有著重要作用,是神經(jīng)營養(yǎng)因子家族(NTFs)的一個(gè)成員。BDNF分子質(zhì)量為13 ku,由兩個(gè)成熟亞基以非共價(jià)結(jié)合方式形成同源活性二聚體,成熟亞基含有119個(gè)氨基酸殘基。同源活性二聚體作為配體,結(jié)合受體后,誘導(dǎo)細(xì)胞膜上的酪氨酸蛋白激酶受體B(TrkB)形成二聚體和磷酸化,進(jìn)一步激活細(xì)胞內(nèi)信號(hào),發(fā)揮其生物學(xué)效應(yīng)[11,12]。與神經(jīng)生長因子不同,BDNF主要在中樞神經(jīng)系統(tǒng),維持神經(jīng)脊和外胚層基板的感覺神經(jīng)元,這些神經(jīng)元對神經(jīng)生長因子無反應(yīng)。
近年來的研究發(fā)現(xiàn),BDNF與哺乳動(dòng)物的繁殖機(jī)能有著密切的聯(lián)系,人們發(fā)現(xiàn)BDNF及其高親合力受體TrkB在卵巢組織中表達(dá),而且其表達(dá)水平和卵母細(xì)胞發(fā)育潛能關(guān)聯(lián)性很高。家雞排卵前卵巢卵泡膜細(xì)胞表達(dá)BDNF,家雞排卵前顆粒細(xì)胞和小鼠的卵母細(xì)胞膜上分別有TrkB表達(dá),TrkB基因敲除的大鼠卵泡發(fā)育不良[13-15]。在對哺乳動(dòng)物小鼠和人的研究中,人們發(fā)現(xiàn)排卵前LH分泌量的上升刺激卵泡顆粒細(xì)胞產(chǎn)生大量BDNF,BDNF促使卵母細(xì)胞第一極體釋放并進(jìn)一步誘導(dǎo)胞質(zhì)成熟[16,17]。關(guān)于BDNF在卵巢中的表達(dá)及其對卵巢功能的影響研究,無論從基礎(chǔ)研究還是臨床研究的角度都具有重大利用價(jià)值。
2.2GDNF
GDNF(Glial cell line-derived neurotrophic factor)是膠質(zhì)細(xì)胞源性神經(jīng)營養(yǎng)因子,是幾種不同類型的神經(jīng)元中第一個(gè)被確定的存活因子[18,19]。GDNF成熟肽均有134個(gè)氨基酸殘基,活性形式為二硫鍵連接的同源二聚體糖蛋白,能促進(jìn)神經(jīng)元尤其是多巴胺能神經(jīng)元的生長分化,是治療神經(jīng)退化性疾病如帕金森癥的潛在有效藥物。GDNF家族神經(jīng)營養(yǎng)因子信號(hào)傳導(dǎo)是通過復(fù)合受體途徑實(shí)現(xiàn)的,復(fù)合受體由兩部分組成,第一部分是糖基化的磷脂酰肌醇(GPI)錨定到細(xì)胞表面的蛋白分子,稱為GDNF家族受體(GDNF family receptor-alpha1,GFRA),另一部分是由原癌基因c-ret編碼的蛋白產(chǎn)物(Ret proto-oncogene,Ret),它是一種受體酪氨酸激酶[20]。
雖然GDNF及其受體主要在神經(jīng)系統(tǒng)中大量表達(dá),但人們也在幾種邊緣組織中發(fā)現(xiàn)GDNF及其受體,其中就包括卵巢和睪丸組織[21]。在睪丸組織中,GDNF參與精原細(xì)胞增殖及分化的調(diào)控[22]。通過DNA芯片分析,GDNF在卵巢、卵丘細(xì)胞和顆粒細(xì)胞中均有表達(dá),并且其表達(dá)水平在排卵前明顯上升[16]。在對小鼠的研究中發(fā)現(xiàn),GDNF作為主要生長因子促進(jìn)精原干細(xì)胞的增殖[23]。GDNF及其受體GFRA和Ret在卵母細(xì)胞、卵管和子宮中均有大量表達(dá),GDNF促使小鼠卵母細(xì)胞第一極體的釋放,并通過抑制胚胎細(xì)胞的凋亡促使2細(xì)胞胚胎向囊胚階段發(fā)育[6]。
2.3INSL3
INSL3(Insulin-like factor 3)是胰島素樣因子3,是松弛素-胰島素激素家族的成員之一,由睪丸間質(zhì)細(xì)胞在整個(gè)生命周期內(nèi)穩(wěn)定分泌產(chǎn)生的一種激素,被認(rèn)為可能是比睪丸激素水平更敏感的,能顯示間質(zhì)細(xì)胞功能狀況的指標(biāo)。INSL3基因或其受體基因LGR8/GREAT若發(fā)生突變,則可能會(huì)導(dǎo)致男性患隱睪病[24]。除睪丸組織外,其他類型的組織中也有LGR8/GREAT基因的表達(dá),在發(fā)育成熟的間質(zhì)細(xì)胞中檢測到INSL3,說明LGR8/GREAT-INSL3激素系統(tǒng)在成年個(gè)體內(nèi)可能還擔(dān)負(fù)其他生理功能。在之后的研究中,人們發(fā)現(xiàn)INSL3在出生前后的睪丸間質(zhì)細(xì)胞和出生后的卵巢中特異地表達(dá)[25],排卵前的卵母細(xì)胞中卵巢因子INSL3表達(dá)水平上升,卵巢因子INSL3在卵母細(xì)胞成熟中發(fā)揮了重要作用,其可以激活卵母細(xì)胞外圍體細(xì)胞中INSL3的受體,引起卵母細(xì)胞cAMP水平下降,對GVBD的發(fā)生具有明顯的促進(jìn)作用[4,5]。
2.4Endothelin-1
Endothelin最早是從培養(yǎng)的豬主動(dòng)脈內(nèi)皮細(xì)胞中分離純化出的活性多肽,由21個(gè)氨基酸組成,分子質(zhì)量為2 400 u,N端是2個(gè)二硫鍵將1-15、3-11位置的半胱氨酸連接起來,C端是一些疏水性氨基酸的殘基。Endothelin屬于結(jié)構(gòu)同源肽家族,包括Endothelin-1、Endothelin-2和Endothelin-3,其差別在于個(gè)別氨基酸的殘基。多項(xiàng)研究證實(shí),Endothelin不僅存在于血管內(nèi)皮,維持基礎(chǔ)血管張力與心血管系統(tǒng)的穩(wěn)定,也廣泛存在于包括生殖內(nèi)分泌系統(tǒng)在內(nèi)的各種組織和細(xì)胞中,其在生殖過程中參與生殖活動(dòng)調(diào)控的作用被多次研究報(bào)道[26-30]。在對大鼠的研究中,Endothelin-1能夠有效降低氧化亞氮對早期胚胎的損傷[31]。通過對排卵前卵巢基因芯片的全基因組分析,人們發(fā)現(xiàn)Endothelin-1在小鼠卵巢組織的表達(dá)水平很高,Endothelin-1可以促進(jìn)排卵前卵母細(xì)胞GVBD的發(fā)生[27]。Endothelin有2個(gè)G蛋白偶聯(lián)受體EDNRA 和 EDNRB。EDNRA 對Endothelin-1有很高的特異性,但EDNRB對Endothelin-1、Endothelin-2 和Endothelin-3均具有一致的親和力[32,33]??梢越Y(jié)合Endothelin-1、Anti-endothelin-1及Endothelin-1特異性受體EDNRA,對Endothelin-1在卵母細(xì)胞發(fā)育中的調(diào)控作用進(jìn)行深入研究。
3主要研究方法
通過卵巢因子、卵巢因子特異性受體及卵巢因子抗體,結(jié)合基因芯片、實(shí)時(shí)熒光定量PCR、ELISA、免疫組化、卵母細(xì)胞體外成熟、體外受精、早期胚胎體外培養(yǎng)、囊胚內(nèi)細(xì)胞團(tuán)細(xì)胞數(shù)量及細(xì)胞凋亡評估等,可以對卵巢因子在GVBD、第一極體釋放、胚胎發(fā)生及早期胚胎發(fā)育中的自分泌/旁分泌調(diào)控作用進(jìn)行深入研究。
3.1卵巢因子在細(xì)胞及組織中表達(dá)分析
運(yùn)用基因芯片分析鑒定卵巢因子及其特異性受體在卵巢的表達(dá),通過實(shí)時(shí)熒光定量PCR對卵巢因子及其特異性受體在卵巢轉(zhuǎn)錄物進(jìn)行分析,進(jìn)一步驗(yàn)證基因芯片的結(jié)果,ELISA檢測卵巢因子及其特異性受體蛋白在卵巢、輸卵管和子宮組織中的表達(dá)。分離卵巢表面卵泡中的卵丘細(xì)胞、顆粒細(xì)胞和卵母細(xì)胞,以實(shí)時(shí)熒光定量PCR技術(shù)檢測卵巢因子及其特異性受體在3種細(xì)胞的轉(zhuǎn)錄物,運(yùn)用免疫組織化學(xué)方法定位卵巢因子及其特異性受體蛋白在3種細(xì)胞中的表達(dá)。
3.2卵母細(xì)胞核成熟評價(jià)
卵巢獲取卵丘卵母細(xì)胞復(fù)合體(COCs),通過添加卵巢因子及其抗體,對COCs和裸卵進(jìn)行體外培養(yǎng),研究卵巢因子對卵母細(xì)胞GVBD及第一極體釋放的影響,驗(yàn)證卵巢因子是否充當(dāng)旁分泌因子調(diào)控卵母細(xì)胞的核成熟。
3.3卵母細(xì)胞胞質(zhì)成熟評價(jià)
獲?。茫希茫螅?xì)胞在添加和不添加特定卵巢因子的環(huán)境中培養(yǎng),體外成熟培養(yǎng),然后進(jìn)行體外受精及早期胚胎體外培養(yǎng),評估卵母細(xì)胞受精及受精卵發(fā)育至2細(xì)胞、桑葚胚、囊胚的能力。
3.4細(xì)胞增殖和囊胚細(xì)胞凋亡的評價(jià)
培養(yǎng)液中添加卵巢因子,體外培養(yǎng)早期胚胎,收集擴(kuò)展囊胚,使用TUNEL法處理細(xì)胞,評估卵巢因子對細(xì)胞增殖和細(xì)胞凋亡的影響,通過卵巢因子抗體進(jìn)一步驗(yàn)證卵巢因子的作用。
4存在問題
雖然目前人們研究發(fā)現(xiàn)了許多卵巢因子,并對卵巢因子在卵母細(xì)胞發(fā)育中的調(diào)控作用開展了大量研究,也取得了一些研究成果,但這些研究大多集中在卵母細(xì)胞核成熟階段(GVBD和第一極體釋放),對卵巢因子在卵母細(xì)胞發(fā)育后期的研究較少,從胚胎發(fā)生及早期胚胎發(fā)育角度研究卵巢因子的自分泌/旁分泌調(diào)控作用及其機(jī)制的報(bào)道不多[6,16]。同時(shí),大多研究只是涉及單一卵巢因子對卵母細(xì)胞發(fā)育的影響,對不同卵巢因子在卵母細(xì)胞發(fā)育調(diào)控過程中是互相協(xié)同、階段性分工還是互相拮抗認(rèn)識(shí)不清,對包括BDNF、GDNF、INSL3和Endothelin-1在內(nèi)的卵巢因子,在卵母細(xì)胞發(fā)育調(diào)控過程中的相互作用還有待進(jìn)一步研究。
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