Activity-dependent neuroprotective protein: a novel gene essential for brain formation

Abstract

We have recently cloned the novel homeobox-containing activity-dependent neuroprotective protein (ADNP). In the current study, mouse ADNP was shown to be expressed at the time of neural tube closure, detected at E7.5 and increased on E9.5. Expression was augmented in the brain (E12.5), sustained throughout embryogenesis and regulated by VIP. To assess the function of ADNP, knockout mice were established. Detailed analysis revealed cranial neural tube closure failure and death on E8.5–9.0 of the ADNP-knockout embryos. The expression of Oct4, a gene associated with germ-line maintenance was markedly augmented in the knockout embryos. In contrast, the expression of Pax6, a gene crucial for cerebral cortex formation, was abolished in the brain primordial tissue of the knockout embryos. Thus, Pax6 and Oct4 constitute a part of the mechanism of action of ADNP on brain formation, inhibiting germ-line division while activating morphogenesis. In conclusion, ADNP is identified here as a new key gene essential for organogenesis in the developing embryo and may be implicated as a clinical target associated with proper neurodevelopment.

Introduction

Activity-dependent neuroprotective protein (ADNP) [1], [28] was recently identified as a vasoactive intestinal peptide (VIP)-responsive gene during postnatal brain development [1]. VIP has dramatic effects on embryonic growth at the time of neural tube closure (E8.5–9) [13] and affects brain development and function [9], [14], [27]. VIP provides a neuroprotective milieu [3] by activating glial cells. VIP expression is developmentally determined [8], increases with brain maturation [7] stimulates synapse formation [2] and decreases with aging [8]. The ADNP gene is highly conserved in the mouse [1], human [28] and rat [23], and abundantly expressed in the brain and the body [1], [28]. Pronounced ADNP mRNA expression in the hippocampus [1], cerebral cortex [1], [28] and cerebellum [28] suggests an involvement for the protein in brain metabolism. The deduced protein structure of ADNP contains a homeobox domain profile that includes a nuclear export signal, indicating that ADNP may have nuclear and extracellular functions [12], [28]. ADNP also contains a small eight amino acid peptide sequence termed NAP (NAPVSIPQ) a motif identified by peptide scanning that protects neurons, at femtomolar concentrations, against a wide variety of toxic substances in vitro and in vivo, in models of neuronal injury [1], [10], [11], [17], [20], [24]. The current study was set out to investigate the physiological function of ADNP.