In situ hybridization reveals that Syx1A transcripts are present throuhgout precellularized embryos though they are most prevalent at the posterior pole. After cellularization, Syx1A transcripts are present in all cells and appear to be concentrated near the cell membrane. In stage 9 embryos, transcripts are observed in the anterior and posterior midgut invaginations as well as in the ventral neuroblasts and the ectoderm.

Syx1A transcripts are expressed in a complex pattern throughout development. Up to six transcripts are observed at any given stage on northern blots. In early embryos, the 3.5, 4.2, and 8.0kb transcripts are abundant. In 3-9hr embryos, the 4.2, 8.0, and 9.0kb transcripts predominate. The 7.0 and 12.0kb transcripts appear after 9hr. In first instar larvae, 5 transcripts are prominent. In second and third instar larvae, the number of abundant transcripts is reduced to three and two, respectively. During pupation, 5 transcripts reappear and are also seen in adults.

Syx1A expression is widespread in the embryo prior to stage 12. After this, expression in ectodermal cells has faded and expression is observed mainly in the anterior and posterior midguts, the garland cells, and the CNS. By stage 14, the major sites of expression are the CNS and the garland cells. Weaker expression is observed in the PNS.

Syx1A protein is detected in germarium regions 2 and 3 outlining the membranes of the cyst cells. It continues to be abundantly expressed in the nurse cells during oogenesis stages S1-S8. Levels fade during stages S8 and S9. In early embryos, Syx1A protein is present ubiquitously but is concentrated at the posterior tip where it accumulates under the pole buds. At mitotic cycle 13, the protein is concentrated in hexagonal-shaped outlines that correspond to the cleavage furrows of the cytoplasmic buds. After cellularization it is present in all of the membranes of all cells. During germband extension, it is present in the mesoderm, ectoderm, and invaginating neurectoderm but is excluded from the amnioserosa. Syx1A protein is also present in the adult brain and the synaptic substations of the visual system. In the brain it is concentrated in neuropil regions and is somewhat enriched at synaptic regions such as the lamina and the medulla.

Syx1A protein is enriched in neuromuscular junction synaptic boutons, but is also expressed at high levels throughout the axons of the peripheral nerves.

syx1a protein is present primarily in the CNS and garland cells though some staining is seen in the ectoderm and the midgut in stages 15-17. In the CNS, staining is most prominent along the longitudinal tracts of the ventral nerve cord and brain but is also found in the commissures of the CNS and the axons of the peripheral nerves. In the periphery of the embryo, staining is seen in neuromuscular junctions and at low levels in some cell bodies.