Xenopus bagpipe‐related gene, koza, may play a role in regulation of cell proliferation

Abstract

The homeobox gene koza is a new member of the vertebrate bagpipe-related gene family. Embryonic expression of koza is observed at highest levels in the muscle layer of the somites and, during later development, is restricted to the lateral somitic cells, which correspond to slow twitch muscle tissue. Expression of koza is also observed in the myocardial layer of the heart and in the cement gland. In each of these tissues, koza transcription commences only after the expression of terminal differentiation markers. By injection of synthetic mRNA, we show that overexpression of koza leads to an apparent decrease in the number of cells in the somites. No reduction in cell number is observed when koza is present in neural tissues, suggesting that koza exhibits some tissue specificity in regulation of cell proliferation. Embryonic manipulations show that restriction of koza expression to the slow twitch muscle layer is independent of axial structures but is, at least partly, regulated by signals arising in ectodermal tissue. Finally, in Drosophila, bagpipe expression is regulated by the hedgehog signaling pathway. By using ectopic expression, we show that koza transcription is positively regulated by banded hedgehog. This result indicates that regulation of bagpipe expression by hedgehog signaling is evolutionarily conserved.

A novel role forlbx1inXenopushypaxial myogenesis

“…Owing to the lack of the eh1 domain, it would not be able to repress the target gene. A similar phenotype to lbx1 eh-overexpression is observed when the bagpipe homologue koza is overexpressed in Xenopus (Newman and Krieg, 2002). Bagpipe is a member of the NK-class of transcription factors.…”

Inhibition of the cell cycle is required for convergent extension of the paraxial mesoderm during Xenopus neurulation

“…Composite images of αPH3 stained sections were generated as described (Leise and Mueller, 2002). SYTOX Green (Molecular Probes) nuclear staining was performed on mounted MyoD and XNot sections as described (Newman and Krieg, 2002). Nuclei were counted using a Zeiss AxioScope with a 20× objective.…”

“…2D, panels 1 and 2), and for in situ analyses against MyoD (panels 3 and 4) and XNot (data not shown) to delineate the paraxial and axial mesoderm, respectively (Dosch et al, 1997;Saka and Smith, 2001;von Dassow et al, 1993). Subsequently, the MyoD and XNot sections were treated with the nuclear dye SYTOX Green to detect the position and number of nuclei (panels 5, 6, and data not shown) (Newman and Krieg, 2002). Examination of sagittal sections shows that depletion of Wee2 caused an increase in the number of mitotic nuclei in the paraxial mesoderm by stage 18 of development (compare panels 1 and 2).…”

Evolutionary innovation in the vertebrate jaw: A derived morphology in anuran tadpoles and its possible developmental origin

“…Xenopus laevis has two Nkx3.1 genes, one of which has been dubbed koza. (33) These two genes apparently separated from each other very recently in the evolution of Xenopus. There is no evidence for involvement of koza in the development of craniofacial cartilages.…”

“…The function of koza might instead be to negatively regulate cell proliferation within somites. (33) In mouse, Nkx3.1 also regulates cell proliferation, as demonstrated in prostate and palatine gland development. (34,35) It should be noted that zax and Bapx1 orthologues also have several functions distinct from craniofacial development.…”