Mouse testican-2. Expression, glycosylation, and effects on neurite outgrowth

Mouse testican-2 was cloned, sequenced, and shown to be a proteoglycan with a multidomain structure closely similar to that of the human ortholog, previously described as a calcium binding extracellular matrix molecule of the BM-40/SPARC/osteonectin family (Vannahme, C., Schübel, S., Herud, M., Gösling, S., Hülsmann, H., Paulsson, M., Hartmann, U., and Maurer, P. (1999). J. Neurochem. 73, 12-20). Recombinant mouse testican-2 was used to prepare specific antibodies that allowed the detection of testican-2 in various brain structures but also in lung, testis, and in several endocrine glands. Although the testican-2 expressed in EBNA-293 cells carried both heparan sulfate and chondroitin/dermatan sulfate glycosaminoglycan chains, the tissue form always contained only heparan sulfate. Both tissue-derived and recombinant testican-2 carried N-linked glycans. Tissue-derived forms of testican-2 were detected as proteoglycans of varying size, whereas a portion of the molecules produced by EBNA-293 cells were core proteins, lacking glycosaminoglycans. Both the proteoglycan and core protein forms of testican-2 inhibited neurite extension from cultured primary cerebellar neurons and may play regulatory roles in the development of the central nervous system.