The expression of teneurin-4 in the avian embryo: potential roles in patterning of the limb and nervous system.

Teneurins are type II transmembrane proteins that play important roles in pattern formation in Drosophila, axon fasciculation and organogenesis in Caenorhabidits elegans, and neuronal pathfinding in the visual system of the mouse. There is evidence that a peptide derived from a proteolytic event near the C-terminus of teneurins leads to formation of an active neuropeptide, while processing at and near the transmembrane domain leads to shedding of the extracellular domain into the extracellular matrix and the generation of an intracellular fragment that is transported to the nucleus. In vertebrates there are four teneurins. Here, we have studied the expression of teneurin-4 in the chicken embryo. An antiserum against part of the intracellular domain of teneurin-4 recognizes several low molecular weight bands on immunoblots of embryonic chicken brain homogenates, indicating that teneurin-4 is likely to be processed at one or more predicted proteolytic cleavage sites. Antisera against the EGF-like repeats of the extracellular domain label some mesenchyme in the early embryo, and near basement membranes this labeling partially overlaps with anti-laminin (gamma 1 chain) immunostaining. At embryonic day 7, anti-teneurin-4 labels bundles of axons in the nasal, but not temporal retina. Later in development, retinal expression switches so that teneurin-4 is found in the temporal, but not nasal, ganglion cell layer. Teneurin-4 immunolocalization was also compared with other teneurins in the developing limb, where each teneurin is expressed in distinctive regions. These patterns of expression suggest roles for teneurin-4 in patterning and neuronal pathfinding in the avian embryo.