The two vnd transcript isoforms have different transcription profiles on northern blots. vnd-RA is expressed from 3h of embryogenesis and levels decline in larvae and adults. vnd-RB is not observed in embryos and is present at higher levels than vnd-RA at later stages. In adults, vnd-RB is detected in both head and body by RT-PCR while vnd-RA is only detected in heads. vnd transcripts are detected in the adult gut, retina, and lamina by in situ hybridization. While vnd-RA is detected in both retina and lamina, vnd-RB is only detected in the lamina. In third instar larvae, vnd-RA but not vnd-RB transcripts are detected in CNS cells and they are only detected in neuroblasts on the ventral surface of the ventral ganglion.

vnd transcript expression during neuroblast formation is described. After S1 neuroblast delamination at stage 8, a two-cell-wide stripe in the ventral-most neurectoderm continues to express vnd. After S2 neuroblast delamination at stage 9, and at stage 11, vnd expression is restricted to a single-cell-wide row in the ventral-most neurectoderm. In the neuroblast layer, in addition to all ventral neuroblasts, vnd is also detected in three intermediate S2 neuroblasts (NB1-2, NB6-2, NB7-2) located in the posterior compartment of the hemisegment. vnd expression is also detected in neural progeny underlying vnd-positive neuroblasts.

Expression of vnd is first observed in the blastoderm embryo as two longitudinal stripes that flank the prospective mesoderm. In stage 6, a rough pair-rule modulation is seen in the pattern. During stages 7-8, the two stripes fuse at the ventral midline to form the mesectoderm and the ventral-most part of the neurectoderm. During stage 10, the width of the stripes in the neurectoderm decreases and gaps of two or three nonexpressing cells appears with segmental periodicity. In early stage 11, expression is detected mainly in the medial neuroblasts and their progeny and in small clusters of lateral neural cells. During stage 13, CNS expression becomes restricted to stripes of cells perpendicular to the anterior-posterior axis. Transcripts are also detected in the anterior and posterior midgut. In stage 16, expression is lower in the CNS and restricted to discrete cell clusters and persists in the midgut.

vnd protein is detected in larval and adult gut by immunostaining. vnd-PB protein is detected in larval eye disc posterior to the morphogenetic furrow and in adult photoreceptors in the retina and in the lamina. vnd-PA was not detected in the adult fly brain.

Expression of vnd at stage 9 in the procephalic neurectoderm is broad in the ventral region of the antennal, intercalary and ocular segments. As develop proceeds the pattern becomes more restricted and refined. The pattern of neuroblasts arising from the vnd expressing neurectoderm that also express vnd are primarily ventral and display a dynamic pattern of vnd expression.

Expression in procephalic neuroblasts stage 9-11: tritocerebrum - v2-5; deuterocerebrum - d5, v2, v4, v8; protocerebrum - ad4, cv1-9, pv1-3

vnd protein is first detected in blastoderm embryos, in bilateral stripes that will give rise to the ventral column of the CNS. At stage 8, nuclei of ventral midline cells, as well as bilateral ventral column neurectoderm and neuroblasts express vnd protein. Ventral midline expression disappears at stage 9, but ventral column neurectoderm and neuroblast expression remains high. At stage 11, vnd protein is detected in a complex pattern in some of the neuronal progeny of the ventral column neuroblasts; expression is detected in the pCC interneuron, but not in the sibling aCC motorneuron. In addition to expression in some neurons derived from ventral column neuroblasts, vnd protein expression is also detected in dorsally located neurons that may derive from intermediate or dorsal column neuroblasts that do not express vnd.