Fernandes J J, Celniker S E, VijayRaghavan K
Molecular Biology Unit, TIFR, Bombay, India.
Dev Biol. 1996 Jun 15;176(2):166-84. doi: 10.1006/dbio.1996.0125.
Using markers that are expressed at muscle attachment sites, we have examined the early pupal development (first 36 hr) of Indirect Flight Muscle (IFM) attachments in the fruit fly Drosophila melanogaster. Expression of the Drosophila homologs of vertebrate integrins, the Position-Specific (PS) antigens, is known to differentially mark epidermal (PS1alpha) and muscle (PS2alpha) components of the developing IFM attachment sites. During myogenesis, PS2alpha is detected transiently in imaginal myoblasts that fuse with persistent larval muscles to give rise to the Dorsal Longitudinal Muscles (DLMs), but not in myoblasts that fuse de novo to give rise to the Dorso Ventral Muscles. The integrins are not expressed at attachment sites when the muscle fibers first make their appearance (12-20 hr). Following muscle-epidermal contact, PS1 and PS2 are detected at muscle attachment sites. PS1 expression is at the muscle ends and also in the long epidermal processes that connect the developing muscle fibers to their sites of attachment in the epidermis, while PS2 expression is restricted to the muscle ends. Epidermal cells that will contribute to the adult attachment sites are defined as early as the third larval instar. Both anterior and posterior sites of attachment of the IFMs are marked by the expression of reporter beta-galactosidase activity in a P-element line B14.0, which is an insertion at the stripe locus. B14.0 (stripe) is seen in distinct domains in the wing and leg imaginal discs which give rise to the thoracic cuticle. The expression is maintained during pupal development. The B14.0 (stripe) expressing epidermal cells contact the developing muscle fibers, leading to the formation of the myotendon junction. We show that the dorsal and ventral attachment sites of one group of IFMs, the DVMs arise from two different imaginal discs (wing and leg, respectively), which may explain the differential effect of mutations such as bendless on these muscles. Attachment sites for the other group of IFMs, the DLMs, on the other hand, arise from one imaginal disc (wing). B14.0 (stripe) expression defines epidermal cells of the adult attachment sites and is likely to function during early events leading to the formation of muscle-epithelial contacts. The PS integrins are detected at later stages, suggesting a role in the stabilization and maturation of the muscle-epidermal contacts into myotendon junctions.
利用在肌肉附着位点表达的标记物，我们研究了果蝇黑腹果蝇间接飞行肌（IFM）附着结构的早期蛹发育阶段（最初36小时）。已知脊椎动物整合素的果蝇同源物，即位置特异性（PS）抗原，可差异性地标记发育中的IFM附着位点的表皮成分（PS1α）和肌肉成分（PS2α）。在肌生成过程中，PS2α在与持久性幼虫肌肉融合以形成背纵肌（DLM）的成虫成肌细胞中短暂检测到，但在重新融合以形成背腹肌（DVM）的成肌细胞中未检测到。当肌纤维首次出现时（12 - 20小时），整合素在附着位点不表达。肌肉与表皮接触后，在肌肉附着位点检测到PS1和PS2。PS1在肌端以及将发育中的肌纤维连接到其在表皮中的附着位点的长表皮突起中表达，而PS2的表达仅限于肌端。最早在幼虫第三龄期就可确定将形成成虫附着位点的表皮细胞。IFM的前后附着位点均由P因子系B14.0中的报告基因β - 半乳糖苷酶活性表达标记，该系是在条纹基因座处的插入。在产生胸角质层的翅和腿成虫盘中，B14.0（条纹）在不同区域可见。这种表达在蛹发育过程中持续存在。表达B14.0（条纹）的表皮细胞与发育中的肌纤维接触，导致肌腱连接的形成。我们表明，一组IFM即DVM的背侧和腹侧附着位点分别来自两个不同的成虫盘（翅和腿），这可能解释了诸如无弯曲等突变对这些肌肉的不同影响。另一方面，另一组IFM即DLM在翅上的附着位点来自一个成虫盘（翅）。B14.0（条纹）表达确定了成虫附着位点的表皮细胞，并且可能在导致肌肉 - 上皮接触形成的早期事件中发挥作用。PS整合素在后期被检测到，表明其在肌肉 - 表皮接触稳定并成熟为肌腱连接的过程中发挥作用。
