ems transcripts are expressed at roughly 69-75% egg length in the cellular blastoderm embryo. Beginning at gastrulation, they are expressed in a set of stripes just anterior to the cephalic furrow. Expression of ems in the protocerebral domain of the head is mostly gone by stage 9.

ems transcripts are detected at all developmental stages except adult on northern blots. The peak of expression occurs between 6 and 12 hours of embryogenesis and a second smaller peak is seen in second instar larvae. Transcripts are first detected by in situ hybridization at the syncytial blastoderm stage in a stripe that extends from 70-76% egg length dorsally and 74-89% egg length ventrally. At the cellular blastoderm stage, expression fades in the ventral part of the stripe and to a lesser extent dorsally. At stages 6 and 7, @ems transcripts are expressed anterior to and along the cephalic furrow and in the anlagen for the intercalary and antennal segments and in part of the procephalic lobe. At stage 8, they are observed in lateral regions along the extending germ band and in an anterior dorsal patch at 85-90% egg length. During stage 9, expression is seen in 16 regions along the extended germ band and in the mandibular, intercalary, and antennal segments. By stage 10, staining in the gnathal segments corresponds to the anterior part of each segment and the staining in the abdominal segments occurs around the tracheal pits. Staining is also observed in the primordia of the posterior spiracles. Staining in the optic lobe primordium begins at stage 12. By stage 13, expression is seen in lateral cells of the CNS and in a row of cells immediately posterior to the forming segmental furrows. In stage 14, expression is restricted to the anterior part of the mandibular lobe, the antenno-maxillary complex, the subesophageal ganglion, and the posterior spiracles

ems transcripts are expressed in all stages tested with a peak in 6-12 hr embryos, and high levels in 3rd instar larvae and pupae.

At 0 hr APF, ems is detected in superficial cells located along the periphery of the antennal disc, in the second antennal segment, and at the base of the presumptive arista probably within the epidermal cells of the disc. In the third antennal segment of the disc, initial ems expression is observed at 0 hr APF, and by 2 hr APF this increases to include cells in four semi-circular domains. Expression in these domains broadens by 5 hours APF. ems levels diminish by 8 hr APF and it is undetectable by 12 hr APF. ems is present in a subset of amos-expressing cells but does not overlap ato expression. The time course of onset is similar to amos but it is down regulated earlier. ems is also expressed in a subset of lz-expressing cells and transiently in a subset of the sens-expressing proneural domains from which SOPs are selected. In summary, ems is expressed, together with amos, in a subset of proneural clusters in the third segment of the antennal disc. Its expression is transient in SOPs that are selected from these clusters indicating that it may be involved in the development of a subset of the trochoid and/or bas iconic olfactory sense organs.

ems protein is detected in discrete domains in the procephalic ectoderm of stage 9-11 embryos, including initially 3 domains between the anterior part of the mandibular segment and the posterior of the ocular segment. One of these domains further splits. Additional small domains of expression are observed in another region of the ocular segment and in a dorsal patch of procephalic ectoderm. Expression in procephalic neuroblasts stage 9-11: tritocerebrum - d6; deuterocerebrum - d3, d6, v3, v7; protocerebrum - cv5, pd2, pd5, pd8, pd10, pd15

In stage 6 embryos, the ems protein expression domain is posterior to that of tll, with a 1-2 cell unlabled gap between. By embryonic stage 10, ems protein is distributed in a segmentally striped pattern. At this stage, ems expression colocalizes with tll in the intercalary segment, and is adjacent to tll in the antennal and ocular segments. At stage 15, ems expression is adjacent to tll expression in the embryonic brain.

ems is expressed in two independently regulated patterns that are described in detail. The head specific pattern initiates prior to cellular blastoderm and continues to early germband extension. The metameric pattern initiates after gastrulation and includes expression in lateral neuroblasts, in ectodermal cells at the anterior lateral borders of each segment and in the filzkorper primordia. The region of ems expression in the head is anterior and adjacent to the Dfd expression stripe. In bcd mutants, the blastoderm head specific ems staining is absent while the later metameric pattern is unaffected.