Newman CS and Krieg PA (2002), Xenopus bagpipe-related gene, koza, may play a ...

XB-ART-6117

Dev Dyn 2002 Dec 01;2254:571-80. doi: 10.1002/dvdy.10186.

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

Newman CS , Krieg PA .

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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.

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Species referenced: Xenopus
Genes referenced: actc1 actl6a mlc1 mlh1 myh1 myh4 myh6 myl11 nkx3-1 shh

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Figure 4. Expression profile of somitic markers by whole-mount in situ hybridization. Embryos are midneurula (stage [st.] 18, A,D), late neurula (st. 28, B,E,H), or early tail bud (st. 33, C,F,G,I). All images are lateral views with the exception of A and D, which are dorsal views. In all cases, anterior is to the left. A-C: Embryos stained for koza expression. D-F: Embryos assayed for myosin light chain (MLC) expression. Note the more posterior extent of MLC staining relative to the koza expression domain, particularly at midneurula. G: Double staining for both koza and alpha -cardiac actin. Areas of overlap appear as dark blue. Cells expressing only alpha -cardiac actinare light blue. Note the region of light blue staining in the posterior-most paraxial mesoderm. H,I: Embryos assayed for MHC E19 expression. Like MLC, the MHC E19 probe stains paraxial cells posterior to the koza expression domain.

Figure 5. Histologic analysis of embryos stained for somitic markers. All sections are transverse, through the middle of the trunk. A-D: Embryos stained for koza at late neurula (stage [st.] 28, A), early tail bud (st. 32, B), late tail bud (st. 40, C), and mid-tail bud (st. 37, D). Note the progressively more restricted pattern of koza expression. D: koza transcripts are visible in the myocardial layer of the heart (arrow) but not in the endocardium (arrowhead). E: Early tail bud embryo (st. 32) stained for MHC E19. Note that the pattern of expression is very similar to that of a similarly staged embryo stained for koza (B). F: Late tail bud embryo (st. 40) probed for myosin light chain (MLC). In contrast to koza at this stage (C), MLC is expressed throughout the myotome. Scale bars = 200 microns in A-F.