Appum, a Drosophila Homolog of pumilio in the Pea Aphid: Cloning, Developmental Expression, and Presumptive Roles in Posterior Patterning

Appum：果蠅pumilio同源基因在豌豆蚜之選殖、發育表現、參與胚胎後端形塑之角色探討

鍾成侑(Chen-Yo Chung) ； 陳柔含(Jou-Han Chen) ； 張俊哲(Chun-Che Chang)

《台灣昆蟲》 33卷3-4期 (2014/02) Pp. 237-252

https://doi.org/10.6661/TESFE.2013017

摘要

已知形態發生素（morphogens）之濃度梯度為許多動物早期胚胎發育所使用之位置訊息。此一梯度之建立，端賴聚集在胚胎當中的信使核糖核酸（mRNA）轉譯是否受到準確的抑制調控。以果蠅早期胚胎發育為例，抑制母系hunchback（hb）mRNA之轉譯乃透過Nanos（Nos）及Pumilio（Pum）這兩個蛋白質所組成的複合體，結合hb mRNA的3'非轉譯區（3' untranslated region, 3' UTR）所致。由於Nos在合胞囊胚（syncytial blastoderm）的後端濃度最高，因此hb轉譯抑制之強度也由後端至前端逐次遞減，與Nos之梯度反向。這樣一來，Hb蛋白的濃度梯度遂由前到後被建立起來。除了果蠅，以Nos/Pum複合體來抑制基因轉譯之機制也被發現在其它的模式動物當中。因此，我們推測豌豆蚜亦保有此一機制，並於其中選殖到果蠅pumilio的同源基因Appum，以及運用全體原位雜合技術偵測Appum mRNA在無性世代卵、胚的發育表現。實驗結果顯示：在卵與胚胎發育的過程中Appum的三個mRNA異構物皆呈現均勻分布之現象。由此推測，Appum之功能並不倚賴mRNA的非對稱聚集，或藉由局部訊息誘導使mRNA集中。結合先前所發現之Aphb/ApHb與Apnos/ApNos發育表現結果，我們剖析了ApPum蛋白在胚胎後端形成過程所可能扮演的角色。希冀上述針對Appum所進行之實驗和討論，能為日後ApPum之功能解析奠定重要基礎。

關鍵字

胚胎發育 ； 基因異構物 ； 原位雜合 ； 孤雌胎生 ； 轉譯抑制

並列摘要

Gradients of morphogens act as positional information to set the body plan during early development in many animals. Formation of a morphogen gradient usually relies on translational control of mRNA. During early embryogenesis in Drosophila, for example, translational repression of maternal hunchback (hb) is mediated by the 3' untranslated region (UTR) bound by the complex of Nanos (Nos) and Pumilio (Pum). The anteroposterior gradient of Hb thus forms in the syncytium because a reverse gradient of Nos is established from posterior to anterior. Apart from Drosophila, the Nos/Pum-mediated translational repression has been identified in other animal models. We thus assume that this mechanism is also conserved in the asexual pea aphid Acyrthosiphon pisum. In this study we cloned Appum, a Drosophila homolog of pum in the pea aphid, and analyzed its developmental expression in asexual oocytes and embryos. Whole-mount in situ hybridization showed that three isoforms of Appum mRNA were evenly expressed throughout oogenesis and embryogenesis, suggesting that function of Appum mRNA does not dependent on asymmetric localization or local signal induction. Combining the known expression patterns of Aphb/ApHb and Apnos/ApNos, we proposed potential roles of ApPum in posterior patterning of the asexual pea aphid. Taken together, we expect that this study can pave a path for functional assay of ApPum in the future.

並列關鍵字

embryogenesis ； gene isoforms ； in situ hybridization ； parthenogenetic viviparity ； translational repression