Sp1 is expressed in the entire leg imaginal disc except in the most proximal ring of cells that will become the body wall. In the antennal disc it is expressed in a medial ring of cells along the proximal-distal axis. No expression is observed in the wing, haltere, or eye discs. Sp1 expression overlaps the expression of btd.

Sp1 is maternally contributed and the earliest embryonic expression is observed in the brain. Later, strong expression is seen in the limb primordia of the antennae and legs and in a punctate pattern in the ventral nerve cord.

Sp1 transcripts are expressed in the nurse cells and transported into the developing oocyte. Transcripts are detected in the early embryo but are not detected by the blastoderm stage. Later in development transcripts are detected in the larval brain and in the ventral imaginal discs (in the antennal but NOT eye disc, and the leg discs).

Sp1 transcripts are expressed in nurse cells during oogenesis and then are transported to the oocyte. They are observed at low levels in preblastoderm embryos but are not detected in the blastoderm. Later they are expressed in the lateral regions of the embryo in the developing peripheral nervous system. In larvae, they are observed in the larval brain and in a subset of imaginal discs. They are found in concentric rings in antennal discs but not eye discs, and in leg discs but not wing discs.