Control of the temporal and spatial Uncx4.1 expression in the paraxial mesoderm of avian embryos

Abstract

Uncx4.1 is a homeobox containing transcription factor that determines the development of the pedicles of the neural arches, transverse processes and proximal ribs. In this paper we characterize the expression pattern of Uncx4.1 during chick embryogenesis with special focus on its expression in the paraxial mesoderm. In the presomitic mesoderm, Uncx4.1 is expressed in the caudal halves of the somites I and II. In the newly formed somites, Uncx4.1 expression remains in the caudal somite halves but becomes restricted to the somitocoele and the ventral epithelial wall. After somite compartmentalization, Uncx4.1 is expressed in the caudal half of the sclerotome in a well defined spatial and temporal pattern. Micromanipulations revealed that Uncx4.1 expression in the presomitic mesoderm is independent of signals from the axial structures and presumably induced by the intrinsic Notch/Delta driven oscillator activity that determines craniocaudal somite polarity. In contrast, in the maturing somite Uncx4.1 expression depends on signals from the axial structures. The notochord-floor plate complex is essential for maintaining Uncx4.1 expression in the caudal somite half. The neural tube is necessary for providing sufficient Uncx4.1 positive sclerotomal material to enable development of pedicles of the neural arches and transverse processes.

Role of noggin as an upstream signal in the lack of neuronal derivatives found in the avian caudal-most neural crest

“…Interestingly, the DRG facing the grafted caudal-most somites were irregularly segmented, smaller and more dorsally located than the normal DRG, as was found following the transplantation of a series of posterior half-somites at the place of the entire somites (Kalcheim and Teillet, 1989). However, normal striped Uncx4.1 expression (Schrägle et al, 2004) indicated that the caudal-most somites presented anterior and posterior compartments (Fig. 5H,HЈ), as did the more rostral somites.…”

“…The following chick-specific riboprobes were used: Bmp4 (Francis-West et al, 1994), Cad6B and Cad7 (Nakagawa and Takeichi, 1995), FoxD3 (Dottori et al, 2001;Kos et al, 2001), Msx1 and Msx2 (Coelho et al, 1991;Coelho et al, 1992), Ngn1 and Ngn2 (Perez et al, 1999), Nog (Reshef et al, 1998), Pax3 (Goulding et al, 1993), Snail2 (Nieto et al, 1994), Sox9 (Cheung and Briscoe, 2003), Sox10 (Cheng et al, 2000), Uncx4.1 (Schrägle et al, 2004), Wnt1 and Wnt3a (Megason and McMahon, 2002). The following mousespecific riboprobe was used: mouse (m) Nog (McMahon et al, 1998).…”

The Neural Tube Is Required to Maintain Primary Segmentation in the Sclerotome

“…Size truncation of vertebral bodies has been reported after whole neural tube ablation [Schrägle et al, 2004], confi rming that the neural tube plays a role, although minor, in the development of vertebral bodies. We speculate that the truncations may be a consequence of reduced levels of SHH, which after the removal of the right side of the neural tube is only secreted from the remaining left side of the fl oorplate and the notochord.…”

“…The original studies concluded that the more neural tissue was removed, the less cartilage developed, resulting in increasingly abnormal vertebrae [Strudel, 1967;Hall, 1977], and a recent study reports the complete loss of neural arches after removal of the whole neural tube at the level of the anterior presomitic mesoderm [Schrägle et al, 2004]. Fusion of neural arches after neural tube ablation at the level of already formed somites has also previously been documented [Strudel, 1967;Hall, 1977].…”

“…Hypoplastic cartilage development of the vertebrae has previously been observed after removal of neural tube tissue [Strudel, 1967;Hall, 1977;Schrägle et al, 2004]. The original studies concluded that the more neural tissue was removed, the less cartilage developed, resulting in increasingly abnormal vertebrae [Strudel, 1967;Hall, 1977], and a recent study reports the complete loss of neural arches after removal of the whole neural tube at the level of the anterior presomitic mesoderm [Schrägle et al, 2004].…”