探討澤蛭Helobdella胚胎發育過程中FoxA基因表現的時空分佈

Abstract

早期不同物種之間演化的研究，以物種的形態及生理特徵為依據，用此證明物種之間的親緣關係。兩側對稱動物的胚胎發育過程中，將腸道區域化細分成口部、前腸、中腸以及後腸區域。腸道的結構依照物種適應攝食機制的演化，而有所不同。隨著發育生物學的興起，藉由分子機制的研究發現，在後生動物胚胎endomesoderm中許多轉錄因子保守地參與調節，其中包含了與腸道發育相關的FoxA。因此，藉由同源基因所繪製的系統發生樹，以分子演化的方式預測物種之間的親緣關係，並藉由FoxA的研究探討對於物種腸道發育中的影響。 FoxA全名為Forkhead box A，屬於轉錄因子Fox gene家族，Fox genes早期文獻又稱fork head或HNF-3。在研究文獻指出，Fox家族調控著在胚胎發育過程中內胚層、肝臟、肺臟、以及腹側神經發育的形成。FoxA直向同源的基因在後口動物中，已被證實在腸道發育過程中扮演重要角色，並參與胚胎軸向結構的形成。在原口動物中，FoxA直向同源的基因對於前腸、中腸及後腸的正確發育具有影響力，且在胚胎發育成口部區域有FoxA基因的表現。 本研究以冠輪動物環節動物門的澤蛭Helobdella robusta為研究對象，搭配模式生物間系統發生樹的分析，利用原位雜合技術觀察轉錄因子FoxA在澤蛭胚胎發育前期、中期、晚期過程中，FoxA對於澤蛭胚胎發育過程中時間及空間上所扮演的角色。實驗結果發現，在澤蛭胚胎發育早期，Hro-FoxA3表現在endomesoderm當中，與多毛類在卵裂過程中植物極的表現一致。Hro-FoxA2表現在前腸與後腸區域為FoxA的保守功能。Hro-FoxA1表現於特定神經前趨細胞與在第九時期的Hro-FoxA3表現於腹側神經索處，意味著澤蛭的FoxA同源基因扮演著不同的功能。

According to morphological and physiological characteristics of species to improve genetic relationship in early evolutionary study . Regionalization of gut into pharynx, foregut, midgut and hindgut in Bilateria embryonic development. In recent years, developmental biologists use genetic and molecular techniques to study the embryos development. Orthologs of regulatory genes that specify endomesoderm have different developmental roles in Metazoa. Polychaete annelids have conserved gene expression of transcription factors such as FoxA in endomesoderm. Therefore, study of molecular development can predict phylogenetic relationships and figure out gut formation in embryonic development. Transcription factor Forkhead box A (FoxA) is a Fox gene family member. Fox family regulates embryonic development in endoderm, liver, lung, and the formation of the ventral neural development. In protostomes, FoxA orthologs gene has conserved expression in pharynx, forgut, midgut and hindgut region. FoxA orthologs gene not only plays an important role in gut development, but also involved ventral nerve cord formation in deuterostomes. This study use a in situ hybridization to observe expression patterns of FoxA genes during embryonic development of the leech Helobdella. The results show that Hro-FoxA3 express in endomesoderm during cleavage stage. Hro-FoxA2 conservatively express in foregut and hindgut region. Hro-FoxA1 express in specific neuronal precursor cells and Hro-FoxA3 express in ventral nerve cord during late stage. It is means FoxA orthologs play different role during leech embryonic development.