REGULAR ARTICLE Avian pelvis originates from lateral plate mesoderm and its development requires signals from both ectoderm and paraxial mesoderm Yegor Malashichev & Bodo Christ & Felicitas Pröls Received: 11 July 2007 / Accepted: 12 November 2007 / Published online: 18 December 2007 # Springer-Verlag 2007 Abstract The pelvic girdle is composed of three skeletal elements: ilium, pubis, and ischium. In comparison with other parts of the postcranial skeleton, its development is not well known to date. To elucidate the embryonic origin of the avian pelvic girdle and the signaling centers that control its development, we have performed extirpation and quail-to- chick grafting experiments. The results reveal that the entire pelvic girdle originates from the somatopleure at somite levels 26 to 35. No somitic cell contribution to skeletal elements of the pelvis has been detected. Removal of the surface ectoderm covering the lateral plate mesoderm has revealed that ectodermal signals control the development of the pelvic girdle, especially the formation of the pubis and ischium. The impaired development of the ischium and pubis correlates with the downregulation of Pax1 and Alx4, two transcription factors that control the normal development of the ischium and pubis. Although of somatopleural origin, the develop- ment of the ilium depends on somitic signals. Insertion of a barrier between somites and somatopleure disrupts the expression of Emx2 and prevents normal development of the ilium but does not affect the expression of Pax1 or Alx4 and the development of the pubis and ischium. Thus, the development of the ilium, but not of the pubis and ischium, depends on somitic and ectodermal signals. Keywords Pelvic girdle . Somites . Somatopleure . Emx2 . Pax1 . Alx4 . Chick (White Leghorn, Gallus gallus domesticus) . Japanese quail (Coturnix japonicus) Introduction The vertebrate limb bud is a well-established model in developmental biology. Nevertheless, the development of the proximal elements of the appendicular skeleton, i.e., the limb girdles is not well understood. Some data are available concerning the developmental (Chevallier 1977; Huang et al. 2000; Matsuoka et al. 2005) and evolutionary (Burke 1991a,b; Vickaryous and Hall 2006) origin of the shoulder girdle and the genes controlling its development (Selleri et al. 2001; Pröls et al. 2004; Kuijper et al. 2005). However, our knowledge of the development of the pelvic girdle, especially the ilium, remains controversial (Chevallier 1977; Malashichev et al. 2005). The avian pelvic girdle consists of three bones, viz. the ilium, pubis, and ischium, whose structure and morphological devel- opment have been previously described (Mehnert 1887; Johnson 1893; Baumel et al. 1979; Malashichev et al. 2005). In the avian embryo, the ilium is the first visible skeletal element of the pelvic girdle and can be detected as early as HH-stage 26 (Hamburger and Hamilton 1951) as a local mesenchymal condensation at the position of the prospective Cell Tissue Res (2008) 331:595–604 DOI 10.1007/s00441-007-0556-6 This work was supported by the Alexander von Humboldt Stiftung, by grants from the President of the Russian Federation and by the Russian Foundation for Basic Research (a06-04-49721) to Y.M., and by the Deutsche Forschungsgemeinschaft (SFB 592 A1) to B.C. Y. Malashichev (*) Department of Vertebrate Zoology, Faculty of Biology and Soil Sciences, St. Petersburg State University, Universitetskaya nab., 7/9, St. Petersburg 199034, Russia e-mail: malashichev@gmail.com Y. Malashichev : B. Christ : F. Pröls Institut für Anatomie und Zellbiologie, Abteilung Molekulare Embryologie, Universität Freiburg, Albertstrasse 17, 79104 Freiburg, Germany F. Pröls e-mail: felicitas.proels@anat.uni-freiburg.de