unpaired3 （upd3）目前被推測為Janus Kinase （Jak） / Signal Transducer and Activator of Transcription （STAT） 訊息傳遞鏈配體。JAK/STAT訊息傳遞鏈在發育過程中扮演著極為重要的角色，且在演化上哺乳類及果蠅具有相當高度保留性。果蠅的基因組中有3個可能的Jak/STAT 訊息傳遞鏈配體：Upd、Upd2及Upd3。當中以upd調控眼睛發育的研究較為清楚。已知upd可藉由調控Jak/STAT 訊息傳遞鏈，進而影響眼睛的大小。upd在早期眼碟發育過程，具有促進細胞增生的功能。在果蠅眼睛發育過程中，Upd會從眼碟上的凹溝 （morphogenetic furrow, MF） 起始位置分泌，促進果蠅視覺神經開始分化。upd會透過抑制MF分化的負向因子wingless （wg），且促進正向調控因子decapentaplegic （dpp） 的表現，來影響眼睛發育。而upd2、upd3在果蠅眼睛發育過程中，所扮演的角色仍不清楚。upd2完全喪失功能的果蠅，眼睛大小幾近為正常。然而upd3在果蠅眼睛發育的過程中，所扮演的角色及其調控機制仍不清楚。我的實驗結果發現，upd3大量表達或失去功能時，會影響眼睛的大小。若在upd3突變果蠅中，在眼睛表達upd3 cDNA，則可使眼睛大小恢復。此外，我利用RNA原位雜交方式 （RNA in situ hybridization） 檢測upd3在果蠅眼碟的表現的時間及位置。結果顯示，upd3在早期果蠅眼睛發育時期的確有表現。更進一步檢測upd3是否透過JAK/STAT 訊息傳遞鏈調控眼睛發育，結果發現upd3 可活化JAK/STAT 訊息傳遞鏈。在upd3失去功能的情況下，大量表達Jak （hopTum-l）則可使眼睛大小恢復。綜合以上結果推測，upd3會藉由Jak/STAT訊息傳遞鏈調控眼睛大小。研究upd3影響眼睛發育的調控機制，結果發現upd3會透過促使細胞增生而非影響細胞凋亡，進而影響眼睛大小。另一方面 upd3會經由活化眼睛正向調控因子dpp，但並不影響負向因子wg在眼碟的表達。綜合以上結果，顯示upd3確實為Jak/STAT訊息傳遞鏈的配體，且在果蠅眼睛發育過程中影響細胞增生，並參與視覺神經分化的調控，影響果蠅眼睛的發育。 unpaired3 （upd3） encodes an Unpaired （Upd）-like protein which is a putative ligand of the Janus kinase （Jak） / signal transducer and activator of transcription （STAT） signaling pathway. The JAK/STAT pathway is highly conserved in mammals and Drosophila. It plays multiple distinct roles during developmental processes. There are three unpaired-like genes, upd, upd2 and upd3 in the fly genome. upd is well studied during eye development. It has been shown that upd controls the eye size through the Jak/STAT pathway. Upd is effective for cell proliferation in early eye development. Upd is a secreted protein expressed at the middle of posterior margin of eye disc where differentiation of the photoreceptor neurons starts. It has been shown that upd antagonizes the negative eye regulators wingless (wg) and induces the positive eye regulators decapentaplegic (dpp) expression during eye development. However, the roles of upd2 and upd3 in Drosophila eye development are still unclear. In the upd2 null mutant, the adult eye size is nearly normal. We are interested in whether upd3 is involved in Drosophila eye development. I generated upd3 mutants by P element-mediated excision. The upd3 null mutant is viable and fertile. It showed small eye phenotype. Overexpression of upd3 cDNA induced eye enlargement. These suggest upd3 can control eye size. upd3 expression pattern was detected by RNA in situ hybridization, the result showed upd3 is expressed during Drosophila eye development. To examine whether upd3 controls the eye size through the Jak/STAT pathway, the 10xSTAT92E-GFP reporter was used to detect the Jak/STAT activity. My result showed that upd3 can activate the Jak/STAT activity in vivo. Expression of the constitutive active Jak （hopTum-l） can rescue upd3- small eye phenotype. These results indicated that upd3 acts through the Jak/STAT pathway to control the eye size. To further verify how upd3 regulates eye size, I found upd3 promotes cell proliferation but does not affect apoptosis during eye development. upd3 can induce dpp, the positive eye regulator, but does not affect the wg, the negative eye regulators. These results suggest that upd3 is a ture ligand for the Jak/STAT pathway, promotes cell proliferate and neuron cell differentiation during Drosophila eye development.
