YSL-specific genes show a variety of expression patterns in embryos from gastrula through the 24-h stage. Each group of panels for one particular clone is enclosed by a black line, with the clone name attop left; stages are shown at bottom right. Clone 1091 has similarity to fructose-1,6-bisphosphatase and is expressed in the YSL at all stages tested (A,B). Clone 1279 is highly homologous to the HNF4 transcription factor. It is expressed in the YSL during early stages (C,D) but not by 24 h (E); expression seen at 24 h is not in the YSL. Clone 1327 has similarity to 4f2/CD98. It is expressed in the entire YSL at early stages (F,G), becomes restricted to posterior YSL at the 3-somite stage (H,I, arrowhead), and expression in the YSL is lost by the 15-somite stage (J); anterior non-YSL expression is indicated by an asterisk. Clone 2834 has similarity to amino acid transporter, solute carrier family 7. It is uniquely expressed in the outer YSL at the shield stage (K, arrowhead). Expression gradually decreases (L) and is lost by 24 h (M). Clone 3371, which is similar to transketolase, is not expressed at gastrula (N) but later becomes expressed in the posterior YSL (O). Clone 3427 is an unidentified sequence that is expressed in the YSL at the shield stage (P) and disappears from the YSL at 24 h but gains a new expression domain in the nervous system (Q). Clone 3525 is similar to, and probably represents, transferrin. It is expressed in the YSL in all stages (R–T); inset in T shows a section, confirming YSL expression. Clone 5041 is an unidentified sequence showing a punctate expression pattern at shield stage (U) and especially at 24 h (W). YSL expression was confirmed by sectioning a shield stage (V) and 24-h embryo (W, inset); the section inV is parasagital and slightly oblique, reducing the thickness of the blastoderm relative to the yolk. Clone 5157 is similar to phosphoenolpyruvate carboxykinase 1 and is expressed in the YSL at all stages tested (X, Y). (40%) 40% epiboly stage; (sh) shield stage; (3s) 3-somite stage; (15s) 15-somite stage; (24h) 24-h stage; (28h) 28-h stage.
