Distribution of slob mRNA. Frontal sections of Drosophila heads were probed with digoxigenin labeled RNA probes for slob. (A) Low magnification to survey entire head section. Antisense slob probes hybridized to the photoreceptors, optic lobe, PI neurons and the surrounding brain cortex. (B) High levels of expression detected in the photoreceptors, lamina and medulla. (C) slob message appears in the PI region. The arrows point to the dorsal medial PI neurons. (D-F) Digoxigenin labeled sense probes of slob reveal no significant labeling. The three panels correspond to the head sections of (A-C).