The Ca ² +-induced methyltransferase xPRMT1b controls neural fate in amphibian embryo

Abstract

We have previously shown that an increase in intracellular Ca 2؉ is both necessary and sufficient to commit ectoderm to a neural fate in Xenopus embryos. However, the relationship between this Ca 2؉ increase and the expression of early neural genes has yet to be defined. Using a subtractive cDNA library between untreated and caffeine-treated animal caps, i.e., control ectoderm and ectoderm induced toward a neural fate by a release of Ca 2؉ , we have isolated the arginine N-methyltransferase, xPRMT1b, a Ca 2؉ -induced target gene, which plays a pivotal role in this process. First, we show in embryo and in animal cap that xPRMT1b expression is Ca 2؉ -regulated. Second, overexpression of xPRMT1b induces the expression of early neural genes such as Zic3. Finally, in the whole embryo, antisense approach with morpholino oligonucleotide against xPRMT1b impairs neural development and in animal caps blocks the expression of neural markers induced by a release of internal Ca 2؉ . Our results implicate an instructive role of an enzyme, an arginine methyltransferase protein, in the embryonic choice of determination between epidermal and neural fate. The results presented provide insights by which a Ca 2؉ increase induces neural fate.calcium ͉ neural induction ͉ protein methyltransferase ͉ Xenopus

Ca2+ coding and decoding strategies for the specification of neural and renal precursor cells during development

“…Furthermore, loss-of-function of kcnip1 has been shown to increase the number of proliferating neural precursors; expand the neural plate (as seen by the enlargement of the anterior expression domain of early neural genes prmt1b, zic3 and sox2); inhibit epidermis and neural crest formation as shown by the reduction in expression of k81 and sox8, respectively; and block expression of n-tub, a marker of neuronal differentiation. These data therefore suggest that extension of the neural plate might be controlled by kcnip1 via transcriptional repression of early neural genes such as prmt1b involved in neural fate specification [29], and/or of sox2 required to maintain neural progenitor identity.…”

“…Among these clones, we identified xmlp, prmt1b, xId3 and p54nrb [29]. Xmlp encodes a MARCKS-like protein, which is a substrate for protein kinase C (PKC) [26,28]; prmt1b is the Xenopus homologue of the mammalian arginine methyltransferase PRMT1 gene [29]; xId3 is an HLH factor that acts as dominant negative inhibitor of bHLH transcription factors [30]; and p54nrb encodes an RRM-domain protein characteristic of RNA-binding proteins and it has been implicated in pre-mRNA splicing steps [31].…”

“…Xmlp encodes a MARCKS-like protein, which is a substrate for protein kinase C (PKC) [26,28]; prmt1b is the Xenopus homologue of the mammalian arginine methyltransferase PRMT1 gene [29]; xId3 is an HLH factor that acts as dominant negative inhibitor of bHLH transcription factors [30]; and p54nrb encodes an RRM-domain protein characteristic of RNA-binding proteins and it has been implicated in pre-mRNA splicing steps [31]. The spatio-temporal expression pattern of these genes was shown to be restricted to the neural territories and their expression was triggered following an inhibition of BMP signalling by noggin.…”

“…When prmt1b was over-expressed in the neural territories, the expression of the neural precursor gene zic3 was induced. Conversely, the loss of function of prmt1b inhibited the expression of zic3 and impaired anterior neural development in the whole embryo [29]. An identical phenotype was also obtained when embryos were treated with CaV1.2 channel antagonists [8].…”

“…During the specification of neural progenitors in amphibians, prmt1b has been shown to bind directly to Ca 2+ target without requiring de novo protein synthesis [29]. To date, DREAM (i.e., Downstream Regulatory Element (DRE) Antagonist Modulator), is the only Ca 2+ sensor known to bind specifically to DNA and to directly regulate transcription in a Ca 2+ -dependent manner [77].…”