8/3/2023 0 Comments Half wing heartThe transformed metathorax (HT2) shows in about 50% of specimens a dorsal cleft named split thorax. (C) Flies carrying the triple mutation over the TM2, Ubx balancer display a homeotic transformation of T3 to T2 indicated by the presence of additional wings and a second scutellum. (B) Translocations and inversions induced by irradiation led to a chromosomal breakpoint between band 89D and 89E within the balancer chromosome TM2, Ubx (FlyBase: Drysdale et al. The homeotic mutations abx, bx 3, and pbx are located in the third intron and upstream of the Ubx gene and affect cis regulatory elements. (A) Ubx maps to the cytological band 89D. Numbers indicate cells originating from the four pairs of WHPs (A1, first abdominal segment EPC, Even-skipped positive pericardial cell OHS, outflow hanging structure sc, scutellum T2, second thoracic segment T3, third thoracic segment wh, wing heart cartoons of developmental stages adapted from Hartenstein 1993).Ĭytological location of Ubx and its homeotic mutations. WHPs proliferate and undergo passive relocation as well as active migration before their final differentiation into mature wing hearts. (F) Schematic of postembryonic wing heart development. The EPCs anterior to the WHPs remain close to the heart and form the OHS together with the EPCs in A1 (PS6). WHPs lose Tinman expression and relocate in front of the heart. The prospective WHPs are depicted in green, all other EPCs in gray. (E) Schematic representation of stages 13 and 17 embryos illustrating the distribution of EPCs along the anterior–posterior axis. (D) cLSM image of a wing heart expressing handC-GFP (lateral view). (C) Lateral view of a wing heart located in the lateral corner of the scutellum. (B) Epifluorescence image of a pharate adult with bilaterally located wing hearts in the scutellum (dorsal view). The scutellar arm connects the scutellum to the posterior wing vein. (A) Dorsolateral view of an adult thorax showing the location of the scutellum in T2. For permissions, please email: and development of wing hearts. Published by Oxford University Press on behalf of Genetics Society of America. We show that a second pair of functional wing hearts is formed in the transformed third thoracic segment and that all wing hearts originate from the wild-type population of wing heart progenitor cells.ĭrosophila Ubx Ultrabithorax circulation evolution four-winged fly homeotic transformation muscle differentiation myogenesis wing hearts wing maturation. In these flies, the third thoracic segment is homeotically transformed into a second thoracic segment resulting in a second pair of wings instead of the club-shaped halteres. Furthermore, we analyzed the development of wing hearts in the famous four-winged Ultrabithorax (Ubx) mutant, which was first discovered by Ed Lewis in the 1970s. Here we show that the specification of WHPs depends on the regulatory activity of the Hox gene Ultrabithorax. However, adult dipterian flies harbor only one pair of wings and only one pair of associated wing hearts in the second thoracic segment. The embryonic wing heart progenitors originate from two adjacent parasegments corresponding to the later second and third thoracic segments. Mutant flies that lack intact wing hearts are flightless and display malformed wings. This clearing process is essential for the formation of functional wing blades. Immediately after the imaginal ecdysis, these accessory circulatory organs remove hemolymph and apoptotic epidermal cells from the premature wings through their pumping action. In the fruit fly Drosophila melanogaster, proper development of wings requires the activity of so-called wing hearts located in the scutellum of the thorax. Wings are probably the most advanced evolutionary novelty in insects.
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