Signaling by Bone Morphogenetic Proteins and Smad1 Modulates the Postnatal Differentiation of Cerebellar Cells

Abstract

Previous studies have demonstrated that bone morphogenetic proteins (BMPs) activate the Smad1 signaling pathway to regulate cell determination and differentiation in the embryonic nervous system. Studies examining gene and protein expression in the rat cerebellum suggest that this pathway also regulates postnatal differentiation. Using microarrays, we found that Smad1 mRNA expression in the cerebellum increases transiently at postnatal day 6 (P6). Immunohistochemistry and Western blots showed that Smad1 and BMP4 proteins are present in the cerebellum, and that their expression also changes postnatally. The proteins are detectable at P4 -P6, a stage at which most cerebellar cells reside in the external germinal layer (EGL), where they extensively differentiate. The levels become maximal at P8 -P10, when neurons begin to migrate from the EGL into their mature positions in the internal granule layer. In cerebellar cultures prepared at P6 or P10, BMP4 activates Smad1 signaling to modulate cell differentiation. Brief BMP4 application caused Smad1 translocation from the neuronal cytoplasm into the nucleus, where it is known to regulate transcription in association with Smad4. Longer BMP4 treatment promoted the differentiation of both neuronal and non-neuronal cells. By 3 d, neuronal processes appeared more fasciculated, and the level of synaptotagmin, a protein found in synaptic vesicles, increased. In addition, many astroglial cells became more branched and stellate in morphology. The BMP-induced changes were reduced by treatment with antisense oligonucleotides to Smad1 or Smad4. These findings in vivo and in culture suggest that BMP4 and Smad1 signaling participate in regulating postnatal cerebellar differentiation.

Autogenous regulation of a network of bone morphogenetic proteins (BMPs) mediates the osteogenic differentiation in murine marrow stromal cells

“…Numerous experiments in a variety of in vitro models have demonstrated that multiple BMPs, used individually or in various combinations can induce the differentiation of a wide variety of tissues including bone, cartilage, adipose tissue, and muscle [4,8,21,22]. BMP-2 and BMP-7 have further been demonstrated to enhance bone healing in vivo in animals and humans in settings such as spinal fusion, fracture repair and distraction osteogenesis [23][24][25].…”

Cerebellar granule cell precursors can differentiate into astroglial cells

“…It is unknown whether some GCPs also develop into astroglial cells in vivo. Although it has been shown that both Shh (12)(13)(14) and BMPs (23,33) are expressed in Purkinje cells and in the EGL, it is not known whether the levels of these proteins are sufficient to induce some GCPs to develop into astroglial cells. Such differentiation could easily be missed because only a small proportion of GCPs are induced to become astroglial cells in culture by Shh and BMPs.…”

“…Taken together, these results suggest that immature GCPs treated with Shh-N and BMP2 differentiate first into the GFAPand neuronal marker-positive cells and then finally into GFAPpositive, S100-␤-positive, neuronal marker-negative, and differentiated astroglial cells. initiate the program of granule cell specification, and Angley et al (23) provided evidence that BMP4 might participate in regulating postnatal granule cell and astroglial cell differentiation. Several laboratories have shown that Shh produced and released by Purkinje cells is a potent mitogen for GCPs (12)(13)(14)(15)24).…”

“…Also, Dahmane and Ruiz-i-Altaba (13) reported that Shh induces the differentiation of Bergmann glia. Because both BMPs (23) and Shh (12)(13)(14) are expressed in the postnatal cerebellum, we examined the effect of both factors administered together to cultured GCPs. We find that a small proportion of the GCPs differentiate into astroglial cells in the presence of both BMPs and Shh but not in the presence of either protein alone.…”

TGF-β Family Signaling in Neural and Neuronal Differentiation, Development, and Function

“…Hindbrain roof plate cultures express Bmp6, Bmp7, and Gdf7 and these factors are sufficient to induce cerebellar granule neurons (Alder et al 1999;Machold et al 2007). BMP-4 and BMP-6 stimulate differentiation and promote survival of granule neurons (Angley et al 2003;BarnedaZahonero et al 2009), whereas targeted inactivation of Bmpr1a and Bmpr1b in mice results in fewer cerebellar granule neurons, causing a smaller cerebellar cortex without foliation (Qin et al 2006). Application of noggin to the developing midbrain -hindbrain border results in complete loss or dorsal shift of Phox2-positive neurons.…”