Pair-rule gene expression in the somitic stage chick embryo: association with somite segmentation and border formation

Abstract

In vertebrates, metameric organization is highlighted by the formation of somites from mesenchymal cells of the segmental plate which then differentiate into dermamyotomal and sclerotomal tissues. The resegmentation of the sclerotome into rostra1 and caudal halves follows, coincident with the production of specific extracellular matrix molecules at the abutment of these two cell types. Ultimately, cells from the caudal sclerotome migrate ventrally and contribute to the chondrogenic prevertebrae. The objective of this work is to investigate the molecular steps regulating these events. Our study is focused on the paired-box containing genes, which have been implicated in delineating boundaries early in development. A chick embryo system, which is readily accessible to manipulation and observation during early development, is used in this study. We have identified the existence of the paired-box motif in the chicken genome by polymerase chain reaction and hybridization with the mouse Pax i paired-box sequence. Expression of paired-box genes occurs early in development as shown by Northern analysis, and is localized by in situ hybridization to the edge of each somite, a patch at the central core of each somite, and the periphery of the neural tube. This specific spatial pattern of expression is consistent with the hypothesis that the pair-rule genes function as effecters of border formation in the early embryo. Moreover, the patch of positive cells at the center of a resegmenting somite appear to migrate ventrally, and may contribute to structures of the prevertebrae. These findings are relevant to our understanding of the mechanism of somite resegmentation and implicate the involvement of pair-rule genes in the process.

Chicken Pax-1 gene: structure and expression during embryonic somite development

“…5A, B, E), strongly indicating that it is associated with the sclerotomal component of the somite, and that it is subsequently a characteristic of the caudal condensing half of the sclerotome. This pattern is in agreement with our previous in situ hybridization findings using histological sections probed with the murine Pax-1 paired-box sequence [32], the recent findings by Johnson et al [24], and Ebensperger et al [18], as well as Dietrich and Gruss [15]. Specifically, Pax-1 expression is associated with those sclerotomal cells which are condensing and initiating ventral migration toward the notochord.…”

“…A number of investigators have conjectured that expression of Pax-1 is a requisite feature of the ventralization of the somite, i.e., the formation of the sclerotome [16,24,27,50]. In addition, we have previously proposed that the Pax-1 gene product may act to delineate or maintain the boundary of the sclerotome, as well as circumscribing the re-segmentation borders of the sclerotome [32]. The latter proposed role is extrapolated from our detection of Pax-1 first in the central cells of the somitocoel, which is situated in the middle of the somite (also reported by Johnson et al [24]), and then finally preferentially in the condensing caudal half of the sclerotome.…”

Engineering Musculoskeletal Grafts for Multi-Tissue Unit Repair: Lessons From Developmental Biology and Wound Healing

“…During trunk musculoskeletal development, somites are initially comprised of sclerotome and dermomyotome regions only but subsequently subdivide into the sclerotome, syndetome, myotome, and dermatome, which contribute toward bone, tendon, muscle, and skin elements, respectively ( Cserjesi et al, 1995 ; Schweitzer et al, 2001 ; Wolpert et al, 2002 ; Mitchell and Sharma, 2005 ; Thomopoulos et al, 2010 ; Berendsen and Olsen, 2015 ; Endo, 2015 ; Jensen et al, 2018 ). Patterning signals including Sonic hedgehog (SHH; Fan and Tessier-Lavigne, 1994 ; Bumcrot and McMahon, 1995 ; Musumeci et al, 2015 ), Noggin ( Berendsen and Olsen, 2015 ; Musumeci et al, 2015 ), Wingless/Integrated (Wnt), Neutrophin, and Fibroblast growth factor (FGF) as well as transcription factors including paraxis, paired box protein (PAX)-1, and PAX-9 are crucial to somite development ( Love and Tuan, 1993 ; Smith and Tuan, 1995 ; Barnes et al, 1996a , b , 1997 ; LeClair et al, 1999 ; Alexander and Tuan, 2010 ). Within the sclerotome, cells form mesenchymal condensations that contribute to skeletal formation indirectly ( via cartilaginous endochondral bone formation) or directly ( via intramembranous bone formation; Berendsen and Olsen, 2015 ).…”

“…Within the sclerotome, cells form mesenchymal condensations that contribute to skeletal formation indirectly ( via cartilaginous endochondral bone formation) or directly ( via intramembranous bone formation; Berendsen and Olsen, 2015 ). Disrupting Pax1 expression using antisense oligonucleotides or valproic acid disrupts sclerotomal differentiation to cause skeletal defects ( Love and Tuan, 1993 ; Smith and Tuan, 1995 ; Barnes et al, 1996a , b , 1997 ; LeClair et al, 1999 ; Alexander and Tuan, 2010 ). As somite development progresses, a group of cells migrate away from the dorso-lateral edges of the dermomyotome toward the original boundary of the sclerotome and dermomyotome ( Musumeci et al, 2015 ).…”

The dysmorphic cervical spine in Klippel-Feil syndrome: interpretations from developmental biology

“…[4,53,54] These two genes (Pax-1 and -9) control segmentation of the somites and sclerotomes to establish intervertebral boundaries. [33] In particular, the Pax-1 gene has been found to be pivotal in the reorganization of the sclerotome. [11] Normally, signaling from the intact notochord and/or the floor plate of the neural tube (by signal proteins such as Sonic hedgehog; see Left-Right Asymmetrical Fusion) is necessary for the occurrence of sufficient Pax-1 gene expression in somites and in sclerotomes during primary segmentation, which, in turn, is required for the formation of the ventral parts of the vertebrae [30,60] (Fig.…”