Alterations in Msx 1 and Msx 2 expression correlate with inhibition of outgrowth of chick facial primordia induced by retinoic acid

Abstract

Spatially-restricted expression domains of Msx 1 and Msx 2 in the developing chick face suggest that they may play a role in epithelial-mesenchymal interactions governing outgrowth of facial primordia. Retinoid application to developing chick faces reproducibly inhibits upper beak outgrowth but the lower beak is unaffected. In the normal face, high levels of Msx gene transcripts in upper and lower beak primordia correlate with regions of outgrowth. Following retinoid treatment, Msx 1 and Msx 2 transcripts are rapidly down-regulated in upper beak primordia where outgrowth is inhibited, but remain largely unchanged in lower beak primordia, where outgrowth is unaffected. Decreases in gene expression precede retinoid-induced morphological changes in the upper beak, suggesting that Msx gene products are involved in mediating the effect of retinoids on facial development.

Fate map of the developing chick face: Analysis of expansion of facial primordia and establishment of the primary palate

“…Application of BMPs to the face increases cell proliferation and induces expression of Msx-1 (Barlow and Francis-West, 1997). Msx-1 is a homeobox-containing gene that has been proposed to play a role in facial outgrowth (Brown et al, 1993(Brown et al, , 1997Mackenzie et al, 1991Mackenzie et al, , 1992Mina et al, 1995;Nishikawa et al, 1994;Suzuki et al, 1991). The pattern of expression of Msx-1 (and the related Msx-2) in the mesenchyme of the face closely correlates with areas, that, from this study, expand most.…”

“…The regions that are affected are those that express the retinoic acid receptor RAR␤ (Rowe et al, 1992). and retinoic treatment also results in reduced levels of Msx-1 and Msx-2 in these regions (Brown et al, 1997).…”

Msx1 and Msx2 promote meiosis initiation

“…Although RA has been shown to promote meiosis (Bowles et al, 2006;Koubova et al, 2006), meiosis can occur without RA signalling (Kumar et al, 2011). Existing literature concerning the role of RA in Msx gene regulation appears to be contradictory (Brown et al, 1997;McGonnell et al, 2001;Shen et al, 1994;Yokouchi et al, 1991). In this study, Msx1 and Msx2 were both overexpressed after RA treatment in the foetal gonads.…”

Morphoregulation of avian beaks: Comparative mapping of growth zone activities and morphological evolution

“…Collagen I expression increased after BMP4 was misexpressed in the cartilage. MSX genes are markers for regions of high proliferation during facial patterning (Brown et al, 1997). Msx1 and -2 have been shown to be expressed in the mesenchyme along the lateral edges of the FNM, MXP, and MDP up to stage 24 (Barlow and Francis-West, 1997).…”