Expression was examined at four phases of embryonic stage 5. slp1 is initially expressed in a nonperiodic gap-like pattern in the anterior, which begins to resolve into stripes in phase 2 (5-17'); however, the full 7-stripe pattern arises only during phase 3 (17-30'). The stripes emerge fully refined, with sharp, evenly spaced stripes.

slp1 is expressed in 14 two-cell-wide stripes, corresponding to the two posterior-most cells in parasegments 1-13 as well as a stripe 0 that is anterior to parasegment 1. There is also expression in a band of dorsal cells anterior to the presegmental region.

slp1 transcripts first appear in 0-3hr embryos and show maximal expression in 3-6hr embryos. Levels fall off steadily until the end of embryogenesis. Transcripts are also expressed in first and third instar larvae. slp1 transcripts are first detected by in situ hybridization in a dynamic gap-gene-like pattern in stage 4 embryos. From stage 5, a metameric pattern develops with six 2-cell-wide stripes appearing posterior to the head stripe. The anterior stripes appear first, followed by more posterior stripes. Stripes also develop ventrally first and then spread dorsally. The stripes remain unconnected on the dorsal side. After the primary stripes are fully established, secondary stripes develop in alternate segments. They also accumulate from anterior to posterior. They are detected laterally first and then spread in the dorsal and ventral directions but never connect on the dorsal side. By stage 6, the secondary stripes are established. They are weaker and don't extend as far dorsally as the primary stripes. During germ band extension, the stripes broaden to 4-5 cells and an additional stripe appears at the tip of the germ band. Segmentally repeated lateral cell clusters that are connected to the ventral stripes by thin stalks also express slp1. A complex pattern of slp1 expression is also observed in the head during germ band extension. The metameric pattern fades as the germ band retracts. Expression is lost in the stalk regions connecting the lateral clusters. New expression is observed in epidermal cells forming ventrolateral oblong cell clusters and in dorsal epidermal cells that will fuse at the dorsal midline. This staining fades as dorsal closure is completed. slp1 expression is also observed after germ band retraction in the proventriculus and in the ventral nerve cord. The patterns of slp1 and slp2 gene expression are very similar but slp2 expression is slightly time delayed relative to slp1 and has minor spatial differences. Double labeling with slp and either ftz, en, or eve probes reveals that slp1 and slp2 are expressed in the posterior half of each parasegment just anterior to the parasegmental boundary.

slp1 transcripts are expressed in a gap gene pattern, then a pair-rule stripe pattern, then a segment polarity gene pattern in early embryos. The same pattern is observed for slp2 transcripts.

slp1 protein is expressed in the same subset of medulla forming neuroblasts as slp2.

slp1-protein is expressed in the developing larval medulla in intermediate neuroblasts, which weakly co-express klu-protein. The expression level of slp1-protein gradually decreases from lateral to medial neuroblasts.

At embryonic stage 11, slp1 is localized to the anterior compartment of segments.

Expression in procephalic neuroblasts stage 9-11: tritocerebrum - d2, d6, d7, v3; deuterocerebrum - d1, d4, d7, d8, v2, v3, v5, v6; protocerebrum - ad2, ad8, d8, cd9, cd12, cd19, cv4, cv6, cv8, pd1, pd11, pd15, pd16, pv1, pv3

Stripes alternate with bap and coincide with eve.

At cellular blastoderm, slp1 protein is found in the posterior portion of each even-numbered parasegment, adjacent to but not overlapping eve protein. During gastrulation, secondary stripes appear, just anterior to the ftz stripes. During germband elongation, every parasegment has a slp1 protein stripe adjacent to en, overlapping wg and extending anterior. At stage 10, this stripe is 3-4 cells wide.