根據世界衛生組織（World Health Organization）統計，約15%的夫婦受到不孕症的影響，在男性不孕症病人常見其Y染色體長臂上有片段的缺失，此片段為AZF區域包含DAZ基因，DAZ的同源基因DAZL位於三號染色體，會專一性表現於生殖細胞，是一個含有RNA-recognition motif與DAZ repeat的RNA binding protein，在DAZL基因剔除的動物模式實驗發現會造成生殖細胞的缺失，文獻也指出DAZL會結合不同基因的mRNA進行後轉錄作用的調控，藉由促進不同基因之mRNA的轉譯作用在生殖細胞精子形成過程中行使不同的功能，顯示DAZL在生殖細胞的發育與分化扮演重要的角色。實驗室之前在患有無精子症與少精症的台灣男性不孕症病人篩選到數個核苷酸突變與單一核苷酸多型性的變異，特別是在核苷酸386 (T54A) 位置由adenine變成guanine，此單一核苷酸多型性在不孕症病人較為盛行。為了闡明單一核苷酸多型性對DAZL功能的影響，首先我們先利用RNA免疫沉澱分析並結合deep-sequencing技術篩選DAZL可能作用的mRNA，得到NUDT21、NUP50、KLHL12、KDELR1、VAPA、ABHD2、SUPT5H、MLL3、ATP6AP2等可能是DAZL調控的transcripts，其中NUDT21在文獻中指出會高量表現在老鼠生殖細胞且參與在精子形成過程中的alternative polyadenylation的機制，因此選定NUDT21作為探討DAZL調控機制的標的。利用核酸醣體免疫沉澱分析，結果顯示DAZL透過後轉錄機制調控NUDT21的表現，藉由抑制NUDT21的轉譯作用在生殖細胞扮演重要的角色，但當T54A單一核苷酸多型性DAZL大量表現時會降低與NUDT21的結合作用，因而無法抑制NUDT21的轉譯作用，顯示生殖細胞的DAZL可能會與不同蛋白質結合，來調控不同的基因參與精子形成過程的作用，而單一核苷酸多型性可能會影響與DAZL作用的結合蛋白，進而影響DAZL與下游RNA的結合能力，在後轉錄作用層面進行不同的調控。

Infertility affects 15% of all couples. Deleted in Azoospermia (DAZ) gene was isolated from the AZFc region of the human Y chromosome that is frequently deleted in infertile men. DAZ-like (DAZL) is an autosomal homolog located on chromosome 3p24. In human beings, DAZL expresses in germ cells with different developmental stages, from spermatogonia, meiotic spermatocytes to mature spermatozoa. Although DAZL is essential for spermatogenesis, the exact function remains undefined. It has been proposed that DAZL binds with mRNA expressed in germ cells and control spermatogenesis at the level of translation. However, specific target mRNAs regulated by DAZL in vivo are not clear. Using RNA immunoprecipitation combined with high-throughput sequence analysis, a number of target transcripts, including NUDT21, NUP50, KLHL12, KDELR1, VAPA, ABHD2, SUPT5H, MLL3 and ATP6AP2, were identified. Among these transcripts the regulation of NUDT21, one of the CFIm subunit, by DAZL was studies. NUDT21 are highly expressed in mouse male germ cells and involve in alternative polyadenylation directed by noncanonical poly(A) signals during spermatogenesis. Previously, we have identified several mutations and single nucleotide polymorphisms (SNP) of DAZL, which associated with spermatogenic failure. To characterize the functional role of DAZL polymorphisms or mutations, RNA-IP and S6-IP were used to examine the binding activity and translational efficiency of NUDT21, respectively. The binding activity was increased while the translational efficiency was decreased in the existence of normal DAZL. In contrast, the polymorphism of DAZL, A to G transition at nucleotide 386, was associated with decreased binding activity and increased translational efficiency for NUDT21. These data support NUDT21 as a candidate target of DAZL-mediated translation and suggest that DAZL may indirectly participate in alternative polyadenylation during spermatogenesis.

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