Differential activation of Xenopus homeo box genes by mesoderm-inducing growth factors and retinoic acid.

Abstract

What is the nature of positional information during embryogenesis? By using Xenopus homeo box genes as anteroposterior (A-P) markers, we confirm the findings of others that mesoderm-inducing growth factors and retinoic acid (RA) can provide positional information along the axis of the body. Xenopus tissue culturemesoderm-inducing factor (XTC-MIF) selectively activates an anteriorly expressed homeo box gene {XlHbox 1), while basic fibroblast growth factor (bFGF) activates selectively a posteriorly expressed homeo box gene {XlHbox 6). RA activates expression of the posterior gene XlHbox 6, but not of XlHbox 1. This activation, however, requires exposure to growth factors. The data suggest that growth factors and RA may cooperate with each other to provide positional information in vertebrates.

Transcriptional regulation of the HOX4C gene by basic fibroblast growth factor on rheumatoid synovial fibroblasts

“…This evidence suggests that HOX4C plays a distinct role in the initiation of limb formation. Several lines of evidence suggest that FGF has multiple effects on the expression of HOX genes (23,39,40). For example, in the developing mouse limb, Evx-1, a horneobox-containing gene, was recently identified as a downstream gene in the FGF signal transduction pathway in limb patterning (41).…”

“…The initiation of the limb bud has also been linked to the HOX D cluster (21,22). It has been shown that some HOX genes, such as XIHbox 6 and HOXD1, are activated by bFGF in Xenopus (23)(24)(25). Based on the above findings, we postulated that bFGF, through activation of a HOX gene, is involved in the proliferation and transformation of synovial fibroblasts in the rheumatoid joint.…”

Characterization of the Xenopus Hox 2.4 gene and identification of control elements in its intron

“…At the egg stage, at least four genes encoding retinoidresponsive nuclear receptors are already present in Xenopus (Blumberg et al, 1992). As is the case for other members of the Xenopus Hox 2 complex (i.e., Hox 2.5, 2.3, and 2.7; Cho and De Robertis, 1990;Leroy and De Robertis, 1992), treatment of embryos with retinoic acid increases steady state levels of Hox 2.4. Figure 7 presents the results of RNAse protection assays of embryos treated with retinoic acid.…”

“…For the animalhegetal conjugates, stage 8 blastula embryos were dechorionated manually and animal and vegetal fragments were dissected out in an agar dish containing 1 x MBS as described previously (Cho and De Robertis, 1990). For determination of the regionspecific expression of Hox 2.4, stage 14 and 26 embryos were dissected into fragments using a razor blade.…”

“…Induction was stronger at the higher concentration. Retinoic acid was prepared as described by Cho and De Robertis (1990). Embryos were harvested a t the neurula stage and RNA prepared by the homogenization and proteinase K protocol mentioned above (Wright et al, 1987).…”