背部開口基因Raw為果蠅心肌細胞正常分化所需

Abstract

研究顯示raw為果蠅背部閉合所需，raw籍由影響Dpp基因在胚胎背部的表而執行其功能，raw突變果蠅胚胎背部成開口狀，由於Dpp為維持心臟發育基因(tinman, tin)在背部中胚層表的主要因子，因此我們認為raw可能也俱有心臟發育的功能，以免疫抗體染色方法，我們發現數種心肌細胞，會因raw功能的缺失而消失，這些包括表現enen-skipped(Eve)、Odd-skipped(Odd)及seven-up(Svp)圍心細胞。我們並且注意到形成這些細胞的先趨細胞在胚胎發育的過程中是存在的，但這些細胞在胚胎發育的晚則不復存在，顯見raw並不影響心肌先趨細胞的特化，而是與其正常分化有關。此外先前研究顯示raw可限制Dpp表於外胚層背部閉合的前導細胞，Dpp會因raw功能的缺失而過度表現，由於Dpp是直接調控tin在中層表現的信息因子，我們的確也發現tin大量的表現在raw突變胚胎中。除Dpp外wingless(Wg)也與果蠅心臟發育有關，而當raw功能缺失時Wg的表現也消失，我們推測Wg表現的消失與心肌細胞在胚胎發育晚期的不正常分化有關，更多的研究將可証實我們的推論。

Previous studies have shown that raw functions in dorsal closure by restricting the expression of Dpp in dorsal ectoderm. In the raw mutant embryos the dorsal ectoderm was not closed. Since Dpp also functions in heart development by maintaining the cardiogenic gene, tinman (tin) in the underlying dorsal mesoderm, we believed that raw may play a role in heart development of insect. In this study we have found that raw is indeed required for proper differentiation of various cardial cell types, including even-skipped pericardial cells (EPCs), Odd positive pericardial cells, cardial cells, which are missing in raw mutant embryos. The precursor cells are formed initially, but missing during late embryogenesis, suggesting raw is not required for specification of these cardial cells but, is required for the survival of cardial cell types. As described above raw limit the expression of Dpp in leading edge of the embryos, loss-of-function of raw results in the ectopic expression of Dpp in dorsal ectoderm. Together with the fact that Dpp directly regulates the expression of tin in mesoderm. We expect that tin may ectopic express in mesoderm. Indeed we have observed that tin is ectopically expressed in raw mutant embryos. In addition, we have found that Wg signaling, which is also essential for cardiogenesis of Drosophila, is missing in raw mutant background. We have hypothesized that loss of Wg signaling may count for the loss of various cardial cell types in raw mutants. More studies are in progress to investigate the possibility.