Spatio-temporal patterns of differentiation of whole heads of the embryonic chick as revealed by binding of a FITC-coupled peanut-agglutinin (FITC-PNA).

The spatio-temporal expression of specific binding sites for FITC-labeled peanut agglutinin (Arachis hypogaea) in frozen sections of whole embryonic heads of the chick between embryonic day 2 (E2) and embryonic day 8 (E8) is described. PNA-binding sites are present already at E2 on the external limiting membrane and the ventricular boundary of the neural wall. With progressing differentiation fluorescent bands are formed from the outside of the neural wall radiating inside, forming second layers inside the CNS at later stages. The visual system (retina and tectum) shows remarkably little PNA-binding activity until about E7/8, a time when binding sites in the other brain areas are already most abundant. In the telencephalon a fuzzy distribution of fluorescence is found. A possible significance of this finding for fiber guidance from the retina to the tectum is briefly discussed. Local high activities can be observed in different parts of the brain. Intense bands of PNA-fluorescence on parts of the epidermis, along the eye cups, around the fore- and hindbrain and in the medial part of the mesenchyme delineate early biochemical compartments foreshadowing the succeeding ossification.