Early maskers of neuronal differentiation in DRG: Islet-1 expression precedes that of Hu

The Hu and Islet-1 proteins are early markers of neuronal differentiation in the avian embryo. We here examine which of these markers is expressed first in avian dorsal root ganglia (DRG). Recently we showed that neural tube and DRG cells express Islet-1 after leaving the cell cycle, while sympathetic ganglion cells express Islet-1 while still dividing. Others have shown that Hu is found in cells that take up BrDU in the DRG, suggesting that it is expressed even earlier in the differentiation process than Islet-1. In this study we double-label sections for Hu and Islet-1 at several stages of embryonic development, using a simple antigen retrieval method in paraffin sections. At early stages many more cells are Islet-1(+) than Hu(-). In addition, although many cells express both markers, some Islet-1(+)/Hu(-) cells are observed but the converse is never found. At later stages, almost all DRG neurons express both markers, although a few Islet-1(+)/Hu(-) cells are still observed. Staining for Hu and Islet-1 at a later stage than previously reported shows that neither marker is expressed in DRG satellite cells. Our results suggest that Islet-1 is a useful marker for DRG neurons at earliest embryonic stages, and is likely to be expressed in DRG neurons before the Hu antigen. (C) 2000 Elsevier Science B.V. All rights reserved.