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U. Drescher
Members of the Eph family - the Eph receptor tyrosine kinases and
their ligands the Ephrins - are predominantly and widely expressed in
the developing and adult nervous system (Zhou 1998). In early development, Ephrins and the corresponding Eph receptors are often found
expressed complementarily, subdividing the embryo into broad structural domains (Gale et al. 1996). As the Eph family appears to exert its
function by a repellent mechanism, the complementary expression of
ligands and receptors indicates a patterning function of this family; for
example, the growth ofaxons, or the movement of cells, expressing a
certain receptor is restricted to regions of the embryo devoid of the
corresponding ligand class.
In recent years, the Eph family has been shown to be involved in a
number of processes during neural development, the development of
topographic projections, and the segmental restriction of neural crest
cells, motor axons, and hindbrain segments, to name just a few. Processes outside the nervous system in which this gene family exerts its
function include angiogenesis.
9.2 Receptor-Ligand Interactions in the Eph Family
At present, 14 different receptors and 8 ligands are recognized for the
Eph family, subdivided into 2 classes on the basis of both sequence
homologies and binding specificities: the EphA subclass containing
glycosyl-phosphatidylinositol (GPI) - anchored EphrinA ligands interacting with EphA receptors and the EphB subclass with transmembraneanchored EphrinB ligands interacting with a complementary set of
EphB receptors. This subdivision is followed relatively strictly, and few
exceptions to this classification, such as the EphA4 receptor which is
able to bind to both classes of Ephrin ligands, have been reported.
Within each of the two subclasses, the interaction between receptors
and ligands appears to be highly promiscuous, e.g., each receptor is able
to bind virtually all ligands of the corresponding subclass and vice
versa. This is indicated, for example, by the fact that soluble receptor or
ligand affinity probes (RAP, LAP; Flanagan and Leder 1990) often pick
up the entire set of ligands or receptors during staining of sections.
However, on detailed examination, there is partially considerable variation in the binding affinities between receptors and ligands (e.g., Gale
U. Drescher
Members of the Eph family - the Eph receptor tyrosine kinases and
their ligands the Ephrins - are predominantly and widely expressed in
the developing and adult nervous system (Zhou 1998). In early development, Ephrins and the corresponding Eph receptors are often found
expressed complementarily, subdividing the embryo into broad structural domains (Gale et al. 1996). As the Eph family appears to exert its
function by a repellent mechanism, the complementary expression of
ligands and receptors indicates a patterning function of this family; for
example, the growth ofaxons, or the movement of cells, expressing a
certain receptor is restricted to regions of the embryo devoid of the
corresponding ligand class.
In recent years, the Eph family has been shown to be involved in a
number of processes during neural development, the development of
topographic projections, and the segmental restriction of neural crest
cells, motor axons, and hindbrain segments, to name just a few. Processes outside the nervous system in which this gene family exerts its
function include angiogenesis.
9.2 Receptor-Ligand Interactions in the Eph Family
At present, 14 different receptors and 8 ligands are recognized for the
Eph family, subdivided into 2 classes on the basis of both sequence
homologies and binding specificities: the EphA subclass containing
glycosyl-phosphatidylinositol (GPI) - anchored EphrinA ligands interacting with EphA receptors and the EphB subclass with transmembraneanchored EphrinB ligands interacting with a complementary set of
EphB receptors. This subdivision is followed relatively strictly, and few
exceptions to this classification, such as the EphA4 receptor which is
able to bind to both classes of Ephrin ligands, have been reported.
Within each of the two subclasses, the interaction between receptors
and ligands appears to be highly promiscuous, e.g., each receptor is able
to bind virtually all ligands of the corresponding subclass and vice
versa. This is indicated, for example, by the fact that soluble receptor or
ligand affinity probes (RAP, LAP; Flanagan and Leder 1990) often pick
up the entire set of ligands or receptors during staining of sections.
However, on detailed examination, there is partially considerable variation in the binding affinities between receptors and ligands (e.g., Gale