The expression of teneurin-4 in the avian embryo.

The teneurins are a family of four transmembrane proteins expressed in the developing vertebrate nervous system, though the Drosophila teneurin ten-m is also a pair-rule gene. Whole-mount in situ hybridization was used to localize teneurin-4 transcripts in the chicken embryo. The earliest signal is detected at stage 19 in the somites and limb buds. By stage 20 teneurin-4 transcripts are detected in temporal periocular mesenchyme, branchial arches, diencephalon and somites. Teneurin-4 expression in the limbs changes dramatically during development. Between stages 19 and 21 teneurin-4 expression is concentrated proximally in the zone of polarizing activity. Between stages 24 and 26 teneurin-4 is expressed in the mesenchyme of the anterodistal part of the limb. As in Drosophila, vertebrate teneurins are expressed not only in the nervous system, but also in non-neuronal tissues during pattern formation.