Bone morphogenetic protein-7 enhances dendritic growth and receptivity to innervation in cultured hippocampal neurons G. S. Withers 1 , D. Higgins 2 , M. Charette 3 and G. Banker 1 1 Center for Research on Occupational and Environmental Toxicology, Oregon Health Sciences University, 3181 Sam Jackson Park Rd, Portland, OR 97201, USA 2 Department of Pharmacology, State University of New York, Buffalo, NY 14214, USA 3 Creative Biomolecules, Hopkinton, MA 01748, USA Keywords: dendrite, neuronal culture, osteogenic protein-1, synapse formation Abstract Members of the bone morphogenetic protein (BMP) family of growth factors are present in the central nervous system during development and throughout life. They are known to play an important regulatory role in cell differentiation, but their function in postmitotictelencephalicneuronshasnotbeeninvestigated.Toaddressthisquestion,weexaminedculturedhippocampalneurons followingtreatmentwithbonemorphogeneticprotein-7(BMP-7,alsoreferredtoasosteogenicprotein-1).Whenaddedatthetimeof plating, BMP-7 markedly stimulated the rate of dendritic development. Within 1day, the dendritic length of BMP-7-treated neurons wasmorethantwicethatofcontrols.BythreedaysthedendriticarborsofBMP-7-treatedneuronshadattainedalevelofbranching similartothatof2-week-oldneuronsculturedunderstandardconditions.Several®ndingsindicatethatBMP-7selectivelyenhances dendriticdevelopment.Whiledendriticlengthwassigni®cantlyincreasedinBMP-7-treatedneurons,thelengthoftheaxonwasnot.In addition,themRNAencodingthedendriticproteinMAP2wassigni®cantlyincreasedbyBMP-7treatment,butthemRNAfortubulin was not. Finally, BMP-7 did not enhance cell survival. Because dendritic maturation is a rate-limiting step in synapse formation in hippocampal cultures, we examined whether BMP-7 accelerated the rate at which neurons became receptive to innervation. Using two separate experimental paradigms, we found that the rate of synapse formation (assessed by counting synapsinI-positive presynapticvesicleclusters)wasincreasedsigni®cantlyinneuronsthathadbeenexposedpreviouslytoBMP-7.BecauseBMP-7and relatedBMPsareexpressedinthehippocampus in situ,thesefactorsmayplayaroleinregulatingdendriticbranchingandsynapse formation in both development and plasticity. Introduction The last decade has seen remarkable progress toward identifying factors that regulate axonal development (Goodman & Shatz, 1993; Cohen-Cory & Fraser, 1995; Tessier-Lavigne & Goodman, 1996; Causing et al., 1997). Cell±cell interactions are equally important in regulating dendritic development (Chamak et al., 1987; Clendening & Hume, 1990; LeRoux & Reh, 1995; Dijkstra et al., 1999), but far less is known about the molecular signals that mediate this regulation. A series of recent papers, which demonstrate that bone morpho- genetic proteins (BMPs) induce the formation of dendrites by cultured sympathetic neurons (Lein et al., 1995, 1996; Guo et al., 1998), raise the possibility that BMPs could play a more widespread role in regulating dendritic growth. Bone morphogenetic proteins, members of the TGF-beta super- family of growth factors (Kingsley, 1994), were ®rst identi®ed by their ability to stimulate bone growth (Sampath et al., 1992; Sampath & Rueger, 1994), but their localization and function is hardly limited to the skeletal system. Highly conserved in evolution, BMP family members mediate key aspects of embryonic patterning in Drosophila (Marques et al., 1997), zebra®sh (Kishimoto et al., 1997), Xenopus (Glinka et al., 1997) and mouse (Monsoro et al., 1996). The role of BMPs is perhaps best characterized in formation of the fundamental embryonic axes (reviewed in Graff, 1997; Hemmati & Melton, 1997). Recent evidence indicates that BMPs also play important roles in nervous system development (reviewed in Mehler et al., 1997). Several BMPs and their receptors are present in the CNS (Helder et al., 1995; So Èderstro Èm et al., 1996; Ebendal et al., 1998; Zhang et al., 1998; So Èderstro Èm & Ebendal, 1999), where they have been implicated in control of cell number and phenotype (Basler et al., 1993; Mehler & Kessler, 1995; Gross et al., 1996; Furuta et al., 1997; Mabie et al., 1997, 1999; Li et al., 1998; Reiriz et al., 1999). Bone morphogenetic proteins also modulate the phenotype of autonomic neurons (Fann & Patterson, 1994; Shah et al., 1996; Varley & Maxwell, 1996). Taken together, these reports suggest that BMPs and associated proteins orchestrate the differentiation and development of many types of cells. It is now becoming apparent that BMPs also regulate the development of postmitotic neurons. In particular, BMP-7 (also known as osteogenic protein-1, OP-1), as well as several other members of the BMP family (including BMP-2 and BMP-6), induce dendritic development by cultured sympathetic neurons (Lein et al., Correspondence: Dr G. S. Withers, as above. E-mail: withersg@OHSU.edu Received 17 May 1999, revised 7 September 1999, accepted 10 September 1999 European Journal of Neuroscience, Vol. 12, pp. 106±116, 2000 Ó European Neuroscience Association