Expression pattern of the Rsk2, Rsk4 and Pdk1 genes during murine embryogenesis

https://doi.org/10.1016/S1567-133X(03)00004-8Get rights and content

Abstract

The ribosomal S6 kinase family members RSK2 (RPS6KA3) and RSK4 (RPS6KA6) belong to the group of X chromosomal genes, in which defects cause unspecific mental retardation (MRX) in humans. In this study, we investigated the spatiotemporal expression pattern of these genes during mouse development with emphasis to midgestation stages. Additionally, we analyzed the expression of the phosphoinositide-dependent protein kinase-1 gene, Pdk1 (Pspk1), which is essential for the activation of Rsk family members and thus regulates their function. During midgestation we observed specifically enhanced expression of Rsk2 first in somites, later restricted to the dermatomyotome of the somites, then in the sensory ganglia of cranial nerves and in the dorsal root ganglia of the spinal nerves. High Rsk2 expression in the cranial nerve ganglia persists throughout development and is correlated with Pdk1 expression. In the brain of 2-day-old mice, Pdk1 is expressed in the cortical plate of the cerebral cortex and in the stratum pyramidale of the hippocampus, whereas Rsk2 expression is lower in these structures. For Rsk4 ubiquitous expression at lower levels was observed throughout development.

Section snippets

Results and discussion

The 90 kDa ribosomal S6 family of serine/threonine kinases mediates cellular signaling downstream of the mitogen-activated protein kinase (MAPK) cascade. They are activated by extracellular regulated kinases (ERK1 and 2), Jun kinase, and other cellular stress stimuli. Consequently, a wide variety of cellular functions for RSK proteins has been proposed (Frödin and Gammeltoft, 1999). These range from cell cycle control to gene regulation by direct histone H3 phosphorylation and activation of

Experimental procedures

Embryos were isolated from pregnant C57Bl/6 mice at the times indicated and fixed in 4% paraformaldehyde in phosphate-buffered saline at 4 °C prior to cryostat sectioning. Ten-micrometer sections were mounted on slides. RNA in situ hybridization was performed on whole-body sections from embryos at 9.5–17.5 dpc and specific sections from 2-day-old mice. To investigate the expression pattern of the mouse Pdk1 gene, IMAGE clone 2648327 (AW323652) was used. The 1.9 kb insert of this clone spans the

Acknowledgements

This research project was supported by the Deutsche Forschungsgemeinschaft (HA1082/16-1, 16-2).

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    In these cells, Rsk2 immunoreactivity was primarily localized to the cell soma, with some immunoreactivity in nuclei, consistent with its known subcellular localization (Anjum and Blenis, 2008). Rsk2 was also expressed in cells that had migrated out of the VZ/SVZ into the cortical mantle, consistent with expression in postmitotic neurons, as previously reported (Zeniou et al., 2002; Kohn et al., 2003). Detectable Rsk2 immunoreactivity was decreased at later embryonic timepoints, consistent with the Western blot analysis (data not shown).

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    Thus, as of January 2005, Unigene listed 16 RSK4 ESTs, 289 RSK1 ESTs, 282 RSK2 ESTs, and 351 RSK3 ESTs (www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=unigene), indicating that low RSK4 protein expression is due to low RSK4 mRNA levels. In agreement with this conclusion, Kohn et al. (41) noted that RSK4 shows relatively broad but low expression compared with RSK2 in fetal mouse tissues. Since RSK4 appears to be constitutively activated in cells and may function to suppress Ras-ERK signal transduction and cell proliferation, the expression level of RSK4 may be low in most cell types to allow cell growth.

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