XBtg2 is required for notochord differentiation during early Xenopus development

Abstract

The notochord is essential for normal vertebrate development, serving as both a structural support for the embryo and a signaling source for the patterning of adjacent tissues. Previous studies on the notochord have mostly focused on its formation and function in early organogenesis but gene regulation in the differentiation of notochord cells itself remains poorly defined. In the course of screening for genes expressed in developing notochord, we have isolated Xenopus homolog of Btg2 (XBtg2). The mammalian Btg2 genes, Btg2/PC3/TIS21, have been reported to have multiple functions in the regulation of cell proliferation and differentiation but their roles in early development are still unclear. Here we characterized XBtg2 in early Xenopus laevis embryogenesis with focus on notochord development. Translational inhibition of XBtg2 resulted in a shortened and bent axis phenotype and the abnormal structures in the notochord tissue, which did not undergo vacuolation. The XBtg2-depleted notochord cells expressed early notochord markers such as chordin and Xnot at the early tailbud stage, but failed to express differentiation markers of notochord such as Tor70 and 5-D-4 antigens in the later stages. These results suggest that XBtg2 is required for the differentiation of notochord cells such as the process of vacuolar formation after determination of notochord cell fate.

Btg1 and Btg2 gene expression during early chick development

“…This may be also the case for the expression of Btg genes in the notochord. In Xenopus, Btg2 is expressed in the notochord and translational blockade of this gene results in alterations of the notochord development (Sugimoto et al, 2005). However, we did not detect Btg2 expression in the chick notochord.…”

“…3A,C, and see also Fig. 1F), as reported for its homologues: Xenopus, XBtg2 (Sugimoto et al, 2005), zebrafish Btg-b (Sakaguchi et al, 2001), and mouse Btg2 (Park et al, 2004). In addition, Btg2 mRNA was also detected in the posterior region of the newly formed somites at HH11 (Fig.…”

“…Knock-out mice for Btg1 are not yet available and Btg2Ϫ/Ϫ mice have minor defects in vertebral patterning (Park et al, 2004). Morpholino injection of Btg genes in Xenopus embryos disrupts some aspects of anterior neural development and notochord differentiation (Sugimoto et al, 2005(Sugimoto et al, , 2007Wessely et al, 2005). It has been suggested that some redundant function may exist between different members of the family (Park et al, 2004;Wessely et al, 2005).…”

“…Information about developmental expression of Btg genes is still fragmentary and limited to individual genes in specific developmental processes in amphioxus, xenopus, zebrafish, and mouse (Iacopetti et al, 1994(Iacopetti et al, , 1999Holland et al, 1997;Buanne et al, 2000;Chen et al, 2000;Saka et al, 2000;Sakaguchi et al, 2001;Thisse et al, 2001;Hammerle et al, 2002;Canzoniere et al, 2004;Park et al, 2004;Thisse and Thisse, 2004;Sugimoto et al, 2005Sugimoto et al, , 2007Wessely et al, 2005;Feng et al, 2007), and there is no detailed description of the expression pattern of any member of the family in the chick embryo. To gain insights on the function of these genes during development, and since Btg1 and Btg2 are the more closely related genes in the family, we sought to analyse and compare their expression profile during early stages of chick development.…”

TIS21 /BTG2/PC3 as a link between ageing and cancer: cell cycle regulator and endogenous cell death molecule

“…in Xenopus (Xbtg2) has revealed notochord abnormality, such as short and bent axis of notochord, and failure of differentiation markers of notochord in the later stages, suggesting that XBtg2 was required for the differentiation of notochord cells such as the process of vacuolar formation after determination of notochord cell fate (Sugimoto et al 2005). Furthermore, TIS21 / BTG2 also plays a role in paraxial mesoderm development in zebrafish (Sakaguchi et al 2001).…”