Fig. 1. Expression patterns of the Ubx, Abd-A and Abd-B proteins on the AP axis of the fat body. (A) Patterns produced by antibodies directed against the BX-C encoded proteins on the AP axis of Drosophila larval fat body. Green arrows indicate the larval gonads. (Top) The Ubx pattern in the fat body of a third instar male larva. The expression of the Ubx protein starts from the anterior bridge (white arrows) and ends in a region situated posterior to the gonad (white arrows) while the anterior of the fat body (large arrowheads) and the salivary glands (small arrowheads) appear devoid of signal. (Middle) Expression pattern of Abd-A in the fat body of a third instar female larva. This protein is accumulated more posteriorly than Ubx (arrows) but anteriorly partially overlaps the Ubx domain. Note that Abd-A is not expressed in all nuclei within its domain. (Bottom) The expression pattern of Abd-B in the fat body of a third instar female larva. This protein is the most posteriorly expressed of the three (arrows). However, its anterior limit of expression does partially overlap with the expression of the other two proteins. As with Abd-A, the protein is not expressed in all the nuclei of its domain. Note that the same immunopatterns were observed in both male and female fat bodies. However, the male gonads showed a low level of immunostaining with all the antibodies, while the female gonads lack any staining. At present, it is not possible to determine if this difference is due to a sex specific function of the homeotic proteins in the gonadal mesoderm or to the difference in size of the gonads in the two sexes. (B) The topological relationship of the Ubx, Abd-A and Abd-B staining patterns with the cuticular ectodermal segments (top). The most anterior expression of the Ubx corresponds approximately to T3 while the posterior border is approximately situated in the A6 segment. The Abd-A protein is expressed in a region co-extensive with segments A3-A7. At its anterior limit it is expressed along two external lines of cells in a region corresponding to segment A2. The Abd-B protein is expressed from a region corresponding to the middle of A4 to the posterior end of the fat body. Note that while Ubx seems to be expressed homogeneously along its domain, Abd-A and Abd-B are expressed only in subsets of cells within their domains of accumulation. Another point of interest is that the immunopatterns seem to suggest that the three proteins could be simultaneously expressed in most nuclei in a region corresponding to segments A4-A6. This point deserves to be better analyzed by tripe labelling when appropriate primary antibodies become available.

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