Circulatory System and Fat Body
The organization of the dorsal vessel in the mature embryo is comparable to that in the third instar larva (see Fig. 1 of Rizki 1978a; Rugendorff et al. 1994). In the embryo, the dorsal vessel consists of a tube that extends from the region immediately be
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Chapter 5 Circulatory System and Fat Body
5.1 Structure of the Dorsal Vessel in the Mature Embryo The organization of the dorsal vessel in the mature embryo is comparable to that in the third instar larva (see Fig. 1 of Rizki 1978a; Rugendorff et al. 1994). In the embryo, the dorsal vessel consists of a tube that extends from the region immediately behind the supraesophageal commissure up to the arthrodial membrane in aJ, where it inserts by means of two caudally directed muscles, which connect the posterior tip of the dorsal vessel to an attachment site in a8 (Figs. 5.1, 5.2F). One distinguishes two main sections of the dorsal vessel; one is anterior, extending up to a4, corresponding to the so-called aorta, while the other is posterior, extending throughout as and a6, and called the heart. At any given cross-sectional level, the lumen of the tube is formed by only two cells, one on each side; this lumen is wider in its caudal, cardiac portion than in its anterior, aortic portion. The tube formed by the cardial cells is surrounded by smaller, round, pericardial cells that extend continuously along both aorta and heart; cardial and pericardial cells are both of mesodermal origin (Bodmer et al. 1989; Hartenstein and Jan 1992), and develop from the two longitudinal rows of cells at the dorsal edge of the main mass of somatic mesodermal cells, called mesodermal crests (Poulson 1950), which meet and fuse at the midline with the homologous cells of the other side (Fig. 5.2). Within anterior regions, the dorsal vessel is surrounded by the lymph glands, which in the embryo seem to consist of only two cell masses, rather than three or more as in the third-ins tar larva (Rizki 1978a; Fig. 5.1). In front of the lymph glands, the dorsal vessel runs through the ring gland to terminate by means of filamentous insertions immediately behind the supraoesophageal commissure (Rizki 1978a). Enhancer-trap lines show that the lymph glands develop from the mesodermal crests corresponding to the
J. A. Campos-Ortega et al., The Embryonic Development of Drosophila melanogaster © Springer-Verlag Berlin Heidelberg 1997
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Chapter 5
Circulatory System and Fat Body
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5.1 Structure of the Dorsal Vessel in the Mature Embryo Fig. 5.1 Structure of the dorsal vessel of a stage 17 embryo, dorsal view (A). The dorsal vessel extends in the dorsal midline from segment t3 to a6. Alary muscles (al) attach the dorsal vessel to the apodemes. The dorsal vessel, consisting of the heart posteriorly and the aorta anteriorly, is formed by the cardioblasts (ea), in association with a bilateral row of pericardial cells (pc). In its anterior portion, the dorsal vessel is flanked by the lymph glands (lg) and ring gland (rg). B-G, B' and G' depict the development of the dorsal vessel in transverse sections. During stage 12
(B, B'), precursors of the dorsal vesamnioserosa cells remain attached to sel appear in the lateral part of the the cardioblasts. During late stage 16 mesoderm (ms), called the mesoder- (F), the tr
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