Figure 2

Immunohistochemical detection of ALV viral proteins in certified SPF chicken embryos. (A-D) Transversal sections of ED6 chick embryo heads, processed by IHC against p27 viral protein (A and C) and DAPI (B and D). (A-B) Section corresponding to an embryo from Flock 1 that was negative for endogenous viral protein expression. (C-D) Section corresponding to a similar region of another embryo from Flock 1, showing extensive expression of p27 viral protein in the retinal neuroepithelium (rn), surrounding cephalic mesenchyme (cm) and brain neuroepithelium (bn) (vc: vitreal cavity). (E and F) Transversal sections of the retina of two different ED11 embryos from Flock 4 showing discrete columns of p27 positive cells; notice in F that in some cases only a few cells are positive for endogenous viral proteins (onl: outer nuclear layer; inl: inner nuclear layer; gcl: ganglion cell layer). (G) Transversal section through the lens of an ED6 embryo from Flock 2 showing endogenous expression of p27 viral protein (le: lens; dc: developing cornea). (H) Transversal section of the retina of an ED6 embryo from Flock 1 showing co-expression of p19 (red) and p27 (green) (rn: retinal neuroepithelium; vc: vitreal cavity). Notice the columnar pattern of expression, particularly in the retinal neuroepithelium and the lens. (I-J) Transversal section through the brain of an ED11 embryo from Flock 4; (I) bright field image; (J) immunostaining for p27 viral protein. Small, well defined areas of the developing brain (br) showed positive expression of p27 (arrows); these areas showed a symmetrical pattern, being present in both, right and left brain structures (vc: ventricular cavity). Scale bar in (J) corresponds to 150 μm for A-D; 100 μm for E-F and H; 250 μm for G and 450 μm for I-J.