[xMLP is an early response calcium target gene in neural determination in Xenopus laevis]

In vertebrates, neural induction occurs during gastrulation when ectodermal cells choose between two fates, neural and epidermal. In Xenopus, neural induction has been regarded as a default pathway as it occurs, in dorsal ectoderm, when ventralizing signals (mainly Bone Morphogenesis Proteins, BMPs, potent epidermal inducers) are inhibited by dorsalizing signals, including factors such as noggin, chordin, and follistatin. However, our previous studies demonstrated that an instructive signal triggered by the activation of L-type voltage-sensitive calcium channels, resulting in a transient increase in intracellular free calcium, appears to be a necessary and sufficient requirement to induce the competent ectoderm toward the neural pathway. Here we further explore the relationship between the Ca2+ transient signals observed and the expression of early neural genes. We have performed a subtractive approach to identify the genes which are transcribed early after the calcium signal and involved in neural determination. We have analyzed a candidate gene (xMLP) which encodes a MARCKS-like protein, a substrate for PKC. We show that this gene is activated by a calcium transient signals and induced by noggin overexpression. xMLP is expressed at the right time in presumptive neural territories. The putative role of xMLP in the process of neural induction is discussed.