Figure 5. EN and ABD-A protein expression in Artemia.

EN is in green and ABD-A is in magenta. Anterior is left for Drosophila, up for Artemia this and subsequent figures. (A) Trunk development in selected Artemia larval stages. The gnathal segments are shown in the L2 and L3 stages, otherwise head structures are not represented in these schematics. After the first molt, segmentation begins in the two gnathal segments (mu and ma). Additional thoracic segments emanate from the posterior growth zone, producing an anterior-posterior gradient of development with anterior segments at a more advanced stage of differentiation than the posterior segments. Thoracomers, trunk segments with limb buds, mark the start of limb formation (e.g. T1 of L3 stage Artemia or T11 of L9 stage Artemia). As limb development proceeds, articulation begins and the trunk segments are now known as thoracopods (e.g. T1 of L4 stage or T10 of L9 stage). The thoracopods undergo elongation and further differentiation so that several podites form for each limb and setae develop and elongate. (B,C) L1 to L9 mixed stages of Artemia were stained with Drosophila embryos ectopically expressing Artemia ABD-ACΔ. Detection of EN protein (B) and Artemia ABD-ACΔ protein (C) in Drosophila embryos at stage 11 are shown. In Artemia, EN stripes (which mark the posterior of each segment) are detected in early stages (D,E,F). Panels G and K shows the midline of a stage L9 Artemia. By the L9 stage (G), EN protein is also detected in a few cells in the neuromeres of each segment (arrowhead). ABD-A protein is not expressed to detectable levels in early stages (H,I,J) but is clearly expressed in neuromeres at stage L9 (K, arrowhead). In the L9 stage (G,K) limbs of trunk segments anterior to T6 are fully differentiated. T6 thoracopods have almost finished differentiation. T8 thoracopods have started articulation (vertical furrows visible in panel K) and T9 thoracomers are just about to initiate articulation. ABD-A protein expression in neuromeres have initiated in a few cells in the T8 trunk segment and within all the neuromere cells in the fully differentiated trunk segments from T6 to T1. mu: maxillulary segment, ma: maxillary segment