Assignment of SYNJ1 to human chromosome 21q22.2 and Synj12 to the murine homologous region on chromosome 16C3-4 by in situ hybridization.

Synaptojanin 1 is a polyphosphoinositide phosphatase highly enriched in nerve terminals (McPherson et al., 1996). The NH2-terminal two thirds of the protein encode two distinct inositol phosphatase modules (a 5)-phosphatase domain and a Sac1-like phosphatase domain), while its proline-rich tail interacts with SH3 and EH domain-containing proteins (McPherson et al., 1996; Haffner et al., 1997; Guo et al., 1999; Cremona et al., 1999). Based on its subcellular localization, the putative function of some of its interactors and genetic studies in yeast, synaptojanin 1 was proposed to play a role in clathrin-mediated synaptic vesicle endocytosis, actin function and signaling (Cremona and De Camilli, 1997). Recent studies on knockout mice have shown that the synaptojanin 1 gene is an essential gene whose inactivation produces alteration of synaptic vesicle recycling. In particular, synaptojanin 1, via its effect on the phosphoinositide metabolism, appears to act as a negative regulator of clathrin coats (Cremona et al., 1999). The gene symbol for the human synaptojanin 1 gene is SYNJ1 and the murine gene symbol is Synj1. The mouse gene Synj1 has been previously mapped to mouse X chromosome region D (observation in Woscholski et al., 1998). Our hybridization results refute the X chromosome assignment and extend the known homology between human chromosome 21q22 and mouse chromosome 16C3–4. The mouse gene for synaptojanin 2 (Synj2) was localized elsewhere (chromosome 17A2–3.1, Khvotchev and Sudhof, 1998). Recently, human intersectin, a synaptojanin 1 interactor, has been assigned upstream to the SYNJ1 gene (chromosome 21q22.1→q22.2, Guipponi et al., 1998).