See the embryonic expression pattern of tap at the Berkeley Drosophila Genome Project Patterns of Gene Expression Site.
In the lineage that gives rise to the external sense organs of the peripheral nervous system, the first division of the sensory mother cell gives rise to two second-order precursors, one of which will produce the outer cells that form the external structures of the organ (trichogen and tormogen cells) while the other will form the inner cells of the organ (sheath cells and neurons). In the case of the abdominal chemosensory organs, the lineage produces two types of neurons: two bipolar neurons, which extend their dendrite within the external structures of the organ, and one multidendritic neuron (md) whose dendrites extend under the epidermis and are not connected to the external structure of the organ. Outer and inner cells were distinguished by double labelling with anti-Tap and with 22C10 monoclonal antibody, which labels the membranes of all sensory neurons. The cell containing the Tap protein is localized in the clusters of neurons, and is therefore not one of the outer cells (Gautier, 1997).
Analysis was concentrated on the ventral abdominal poly-innervated organ, the papilla p6, because its two bipolar neurons and their sib md neuron form a small cluster of three cells. The multidendritic neuron is ventral to the other two and is called v'pda. The two bipolar neurons that innervate p6 are dorsal-most and have been collectively called v'es2, since there has been no way to distinguish them from one other. The results suggest that the anterior and posterior v'es2 behave differently, however, and they have been termed v'aes2 (anterior) and v'pes2 (posterior). The anti-Tap antibody appears to label v'aes2, the anterior-most of the two v'es2 neurons. The sheath cell is closely apposed to the neurons, however, and the possibility that Tap is present in the sheath cell cannot be excluded. However, anti-Prospero antibody labels the nuclei of the sheath cells, and anti-Pros and anti-Tap antibodies recognize different cells, confirming that tap is expressed in one of the neurons and not in the sheath cell (Gautier, 1997)
Tap is expressed at a late stage in the development of one type of adult chemosensory organ, the gustatory bristles of the leg, wing and proboscis. tap is also expressed very early in the development of a second type of chemosensory receptor, the olfactory organs of the antenna. The results of behavioral experiments suggest that the ectopic expression of tap affects the response to sugar and salt. The sensitivity to sugar is impared and the sensitivity to salt is increased. It must be noted that the resonse to salt is but an inhibition of the response to sugar, so that the two effects may actually reflect the same cause (Ledent, 1998).
In the pupal wing, immunolabeling reveals expression of Tap from 16 to 22 hours after puparium formation (APF), at the time when the expression of Pox-n is subsiding. Either single cells or pairs of cells are labeled; in the latter case, one cell is usually more intensely labelled than the other cell. Tap is first expressed in a single cell, then in a pair, and finally maintained in only one. The sub-epidermal location of these cells suggests that they are neurons. These results suggests that Tap is first expressed in the neural precursor, then transiently in both daughter cells. It is thought that Tap is expressed in leg chemosensory organs around 10-14 h APF, a period when imaginal discs are refractory to immunolabeling. Tap is expressed in a few cells of the everting leg disc, at positions that suggest that they correspond to the neurons innervating the Keilin organs (Ledent, 1998).
In the case of the proboscis, the precursors of chemosensory organs appear in three waves, at respectively 0, 6, and 24 h APF. At 16 h many clusters of Pox-n-expressing cells are observed. Those clusters near the midline comprise several cells, and correspond to the first wave of precursors. Most other clusters comprise 2-3 cells, and correspond to the precursors of the second wave. This pattern is identical to that observed in the enhancer-trap line A37, which labels all cells of the sensory lineages, suggesting that all organs of the proboscis express Pox-n. The presence of Tap protein is observed from 18 h APF onwards, in single cells or pairs of cells corresponding to the organs of the first wave. Thus in the proboscis as well as in the wing, Tap is expressed in a pattern that largely overlaps the pattern of Pox-n expression, at stages that are consistent with the idea that Tap is expressed at the time chemosensory neurons are just about to, or are beginning to differentiate (Ledent, 1998).
Tap-positive cells are observed in everting antennal discs, at three sites near the base of the third antennal segment. The number of labelled cells at each site increases progressively during the first 6 h APF, from 1-3 to more than 10. This pattern parallels the appearance of precursor cells in this segment as seen in the A101 enhancer-trap line A101, suggesting that Tap is expressed in one subset of olfactory precursors. The position of the labeled cells is consistent with the idea that they may correspond to three large groups of basiconic sensilla found near the junction between the third and the second antennal segment (Ledent, 1998).
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date revised: 16 August 2008
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