[Are embryonic forms of NCAM homeobox receptors?].

In a previous study we demonstrated that the homeobox peptide pAntp was able to penetrate into rat embryonic neurons in culture thus provoking their morphological differentiation [1]. In the present work we have started to analyse the process of penetration of the homeobox peptide. As illustrated in Figure 1 pAntp migrating as a homogeneous 7 kDa band could be recovered in the nuclear fraction 2 hrs. only after its addition to cultured embryonic neurons (lane 2). Penetration and nuclear targeting were quantitatively blocked by preincubating pAntp with its cognate recognition sequence present in the promoter of Hox-1.3 (lane 3) or by incubating the cells with an antibody directed against the NCAM-specific alpha 2-8 polysialic acid (lane 4). Similar inhibitions were observed when the peptide was incubated with double stranded DNA or added to cells deprived of alpha 2-8 polysialic acid by EndoN treatment (not shown). As illustrated in Figure 2, the strong pAntp-induced neurite growth was antagonized when pAntp internalization was prevented by the EndoN removal of PSA. This effect of EndoN was not due to the enzyme itself since morphological differentiation was not inhibited if EndoN was added after pAntp penetration (Fig. 2B). Polysialic acid is composed of long chains of neuraminic acids, each pyranose ring carrying a negatively charged carboxylic group linked to carbon in position 1. NMR studies of the molecule in solution have demonstrated that the alpha 2-8 link between each pyranose ring allows specific and stable helical conformation [2].(ABSTRACT TRUNCATED AT 250 WORDS)