The regeneration of P2 olfactory sensory neurons is selectively impaired following methyl bromide lesion

The capacity of the peripheral olfactory system to recover after injury has not been thoroughly explored. P2-IRES-tauLacZ mice were exposed to methyl bromide, which causes epithelial damage and kills 90% of the P2 neurons. With subsequent neuronal regeneration, P2 neurons recover within their usual territory to equal control numbers by 1 month but then decline sharply to roughly 40% of control by 3 months. At this time, the P2 projection onto the olfactory bulb is erroneous in several respects. Instead of converging onto 1 or 2 glomeruli per surface, small collections of P2 axons innervate multiple glomeruli at roughly the same position in the bulb as in controls. Within these glomeruli, the P2 axons are aggregated near the edge, whereas the remainder of the glomerulus contains olfactory marker protein (+), non-P2 axons, violating the one receptor-one glomerulus rule normally observed. The aggregates are denser than found in control P2-innervated glomeruli, suggesting that the P2 axons may not be synaptically connected. Based on published literature and other data, we hypothesize that P2 neurons lose out in an activity-based competition for synaptic territory within the glomeruli and are not maintained at control numbers due to a lack of trophic support from the bulb.

Differential expression of components of the retinoic acid signaling pathway in the adult mouse olfactory epithelium

Position within a tissue often correlates with cellular phenotype, for example, differential expression of odorant receptors and cell adhesion molecules across the olfactory mucosa (OM). The association between position and phenotype is often paralleled by gradations in the concentration of retinoic acid (RA), caused by differential expression of the RA synthetic enzymes, the retinaldehyde dehydrogenases (RALDH). We show here that RALDH-1, -2, and -3 are enriched in the sustentacular cells, deep fibroblasts of the lamina propria, and the superficial fibroblasts, respectively, of the ventral and lateral OM as compared to the dorsomedial OM. The shift from high to low expression of the RALDHs matches the boundary defined by the differential expression of OCAM/mamFasII. Further, we found that RA-binding proteins are expressed in the epithelium overlying the RALDH-3 expressing fibroblasts of the lamina propria. Both findings suggest that local alterations in RA concentration may be more important than a gradient of RA across the epithelial plane, per se. In addition, RALDH-3 is found in a small population of basal cells in the ventral and lateral epithelium, which expand and contribute to the neuronal lineage following MeBr lesion. Indeed, transduction with a retrovirus expressing a dominant negative form of retinoic acid receptor type alpha blocks the reappearance of mature, olfactory marker protein (OMP) (+) olfactory neurons as compared to empty vector. These results support the notion of a potential role for RA, both in maintaining the spatial organization of the normal olfactory epithelium and in reestablishing the neuronal population during regeneration after injury.

Shaping BMP morphogen gradients through enzyme-substrate interactions

Bone morphogenetic proteins (BMPs) regulate dorsal/ventral (D/V) patterning across the animal kingdom; however, the biochemical properties of certain pathway components can vary according to species-specific developmental requirements. For example, Tolloid (Tld)-like metalloproteases cleave vertebrate BMP-binding proteins called Chordins constitutively, while the Drosophila Chordin ortholog, Short gastrulation (Sog), is only cleaved efficiently when bound to BMPs. We identified Sog characteristics responsible for making its cleavage dependent on BMP binding. "Chordin-like" variants that are processed independently of BMPs changed the steep BMP gradient found in Drosophila embryos to a shallower profile, analogous to that observed in some vertebrate embryos. This change ultimately affected cell fate allocation and tissue size and resulted in increased variability of patterning. Thus, the acquisition of BMP-dependent Sog processing during evolution appears to facilitate long-range ligand diffusion and formation of a robust morphogen gradient, enabling the bistable BMP signaling outputs required for early Drosophila patterning.

Hepatocyte growth factor disrupts cell contact and stimulates an increase in type 3 inositol triphosphate receptor expression, intracellular calcium levels, and apoptosis of rat ovarian surface epithelial cells

The present studies revealed that hepatocyte growth factor (HGF) disrupts cell contact, increases both type 3 IP3 receptor and intracellular calcium ([Ca2+]i) levels and induces apoptosis of rat ovarian surface epithelial cells (ROSE-179 cells). Type 3 IP3 receptor was only increased in cells that lost cell contact. Disrupting cell contact by depleting extracellular calcium (Ca2+) also resulted in an increase in [Ca2+]i levels and an increase in apoptosis. These responses were prevented by the addition of 0.7 mM Ca2+. Actinomycin D and cycloheximide prevented apoptosis that resulted from Ca2+ removal. In situ hybridization studies revealed that type 3 IP3 receptor was expressed at relatively low levels by ROSE-179 cells cultured with Ca2+ but at high levels in the absence of Ca2+. ROSE-179 cells cultured in Ca2+-free medium with type 3 IP3 receptor antisense oligonucleotide lost cell contact but did not show an increase in either type 3 IP3 receptor protein, [Ca2+]i, or apoptosis. The nonsense oligonucleotide did not alter these responses to Ca2+ removal. Thus, the disruption of cell contact by either HGF or Ca2+ depletion increases the expression of type 3 IP3 receptor, which causes an increase in [Ca2+]i and the apoptotic death of ROSE-179 cells.