Biomedical subjects

A M Koppel

Publications and source records attributed to A M Koppel.

5 recordsLinked to original sources

PubMed1999

A dominant negative receptor for specific secreted semaphorins is generated by deleting an extracellular domain from neuropilin-1.

Neuropilins have recently been characterized as receptors for secreted semaphorins. Here, we report the generation of a dominant negative form of neuropilin-1 by the deletion of one of its extracellular domains. Expression of this variant in cultured primary sympathetic neurons blocks the paralysis of growth cone motility normally induced by SEMA-3A (collapsin-1, semaphorin III, semaphorin D) and SEMA-3C (collapsin-3, semaphorin E) but not that induced by SEMA-3F (semaphorin IV). A truncated form of neuropilin-1 that is missing its cytoplasmic domain fails to act as a dominant negative receptor component. These results suggest that neuropilin-1 is a necessary component of receptor complexes for some, but not all, secreted semaphorin family members. Overexpression of dominant negative neuropilins should provide a powerful new method of blocking the functions of secreted semaphorins.

Animals↗

PubMed1998

Collapsin-1 covalently dimerizes, and dimerization is necessary for collapsing activity.

Chick collapsin-1, the first identified vertebrate member of the semaphorin family of axon guidance proteins, repels specific growth cones. Like all family members, collapsin-1 contains within its sequence a semaphorin domain that is necessary for specifying activity. Two additional structural domains of collapsin-1, the immunoglobulin (Ig) domain and the basic tail, each potentiate collapsin-1 activity. We identify in this study another structural feature of collapsin-1 that is necessary for its function. Collapsin-1 covalently dimerizes, and dimerization is necessary for collapse activity. This dimerization is mediated through a cysteine at residue 723, between the Ig domain and basic tail. The semaphorin domain alone is not active since it cannot dimerize. The collapsing activity of the semaphorin domain can be reconstituted when made as a chimeric construct with an immunoglobin Fc domain, which promotes dimerization.

Chromatography, High Pressure Liquid↗

PubMed1997

A role for collapsin-1 in olfactory and cranial sensory axon guidance.

Collapsin-1 is a member of the semaphorin family of signaling molecules that acts as a repellent for growing spinal sensory axons. We have constructed a chimeric collapsin-1/alkaline phosphatase probe to visualize putative collapsin-1 receptors in vitro and in situ. As predicted by the activity profile of collapsin-1, the probe binds spinal sensory tracts, ventral spinal roots, and the sympathetic chain but does not bind retinal axons. In addition, we find that the probe binds sensory axons arising from the olfactory epithelium and some, but not all, cranial sensory nerves. As predicted by these binding studies, in vitro assays demonstrate that primary olfactory sensory, trigeminal, and jugular ganglion growth cones collapse in the presence of soluble collapsin-1. Comparing the expression pattern of collapsin-1 with the trajectories of collapsin-1 responsive axons suggests that in both the spinal cord and the olfactory bulb, collapsin-1 prevents premature entry of sensory axons into their target and helps determine the final location of sensory terminations.

Alkaline Phosphatase↗

PubMed1997

A 70 amino acid region within the semaphorin domain activates specific cellular response of semaphorin family members.

The semaphorin family contains secreted and transmembrane signaling proteins that function in the nervous, immune, and cardiovascular systems. Chick collapsin-1 is a repellent for specific growth cones. Two other secreted members of the semaphorin family, collapsin-2 and -3, are structurally similar to collapsin-1 but have different biological activities. Semaphorins contain a 500 amino acid family signature semaphorin domain. We show in this study that (1) the semaphorin domain of collapsin-1 is both necessary and sufficient for biological activity, (2) the semaphorin domain contains a 70 amino acid region that specifies the biological activity of the three family members, and (3) the positively charged carboxy terminus potentiates activity without affecting specificity. We propose that semaphorins interact with their receptors through two independent binding sites: one that mediates the biological response and one that potentiates it.

Amino Acid Sequence↗

PubMed1997

Secreted chick semaphorins bind recombinant neuropilin with similar affinities but bind different subsets of neurons in situ.

Collapsin-1, a member of the semaphorin family, activates receptors on specific growth cones, thereby inhibiting their motility. Neuropilin, a previously cloned transmembrane protein, has recently been identified as a candidate receptor for collapsin-1. We have completed the cloning of chick collapsin-3 and -5 and show that collapsin-1, -2, -3, and -5 bind to overlapping but distinct axon tracts. We infer that in situ, there are distinct receptors with different affinities for collapsin-1, -2, -3, and -5. In contrast, these four collapsins all bind recombinant neuropilin with similar affinities. Strong binding to neuropilin is mediated by the carboxy third of the collapsins, while the semaphorin domain confers their unique binding patterns in situ. We propose that neuropilin is a common component of a semaphorin receptor complex, and that additional differentially expressed receptor components interact with the semaphorin domains to confer binding specificity.

Animals↗