Abstract
The Drosophila eye-antenna imaginal disc (ead) is a flattened sac of two-layered epithelia, from which most head structures are derived. Secreted morphogens like Wingless (Wg), Hedgehog (Hh), and Decapentaplegic (Dpp) are important for early patterning of ead, but the underlying mechanisms are still largely unknown. To understand how these morphogens function in the ead of early larval stages, we used wg-LacZ and dpp-Gal4 markers for the examination of wild-type and mutant eads. We found that the ead immediately after hatching was crescent-shaped with the Bolwig’s nerve at the ventral edge, suggesting that it consists of dorsal domain. In a subsequent step, transcriptional induction of dpp in the cells along the Bolwig’s nerve was followed by rapid growth of the ventral domain. Both Wg and Hh were required for the formation of the ventral domain. Wg was crucial for the growth of the entire ead, but Hh was essential for cell division only in the dorsal domain. In the ventral domain, Hh regulated dpp transcription. Based on these data, we propose that signaling among distinct groups of cells expressing Wg, Dpp, or Hh in the ead of the first-instar larvae are critical for coordinated growth and patterning of ead.
Highlights
All adult structures are developed from primordia that are initiated from a small number of founder cells whose proliferation and differentiation are controlled by multiple signaling molecules and domain-specific selector proteins [1,2]
1) What is the domain structure of the L1 ead right after hatching? 2) Are there different types of cells in the L1 ead? 3) What are the distinct functions of Hh, Wg and Dpp in the patterning and growth of early eads? 4) Can cells in the L1 ead be correlated with those in the L3 ead? We examined for the first time the expression pattern of L1 and L2 eads in detail, and have shown that different cell types in the L1 ead exhibit distinct responses to morphogens in their growth and patterning
We found that SH53-LacZ driven by dppsh-c was not expressed in L1 and L2 wild-type eads, but detected from the early L3 stage at a very low level in the posterior ventral margin area (Fig. 6B, B’)
Summary
All adult structures are developed from primordia that are initiated from a small number of founder cells whose proliferation and differentiation are controlled by multiple signaling molecules and domain-specific selector proteins [1,2]. The eye-antenna disc (ead) contains primordia for eye, antenna, ocelli, palpus and head cuticles [3,4,5]. Morphogens such as Hedgehog (Hh), Wingless (Wg), and Decapentaplegic (Dpp) are PLOS ONE | DOI:10.1371/journal.pone.0121999. Cell Type-Specific Responses to Morphogens for Early Eye-Antenna Disc important for growth and regional specificity of ead including the initial patterning of the firstinstar (L1) ead [6,7,8,9,10,11,12,13]. Little is understood how ~20 cells of L1 ead respond to these morphogens for their growth and patterning [11]
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