Regulation of bHLH-PAS protein subcellular localization duringDrosophilaembryogenesis

Abstract

The Drosophila Single-minded and Tango basic-helix-loop-helix-PAS protein heterodimer controls transcription and embryonic development of the CNS midline cells, while the Trachealess and Tango heterodimer controls tracheal cell and salivary duct transcription and development. Expression of both single-minded and trachealess is highly restricted to their respective cell lineages, however tango is broadly expressed. The developmental control of subcellular localization of these proteins is investigated because of their similarity to the mammalian basic-helix-loop-helix-PAS Aromatic hydrocarbon receptor whose nuclear localization is dependent on ligand binding. Confocal imaging of Single-minded and Trachealess protein localization indicate that they accumulate in cell nuclei when initially synthesized in their respective cell lineages and remain nuclear throughout embryogenesis. Ectopic expression experiments show that Single-minded and Trachealess are localized to nuclei in cells throughout the ectoderm and mesoderm, indicating that nuclear accumulation is not regulated in a cell-specific fashion and unlikely to be ligand dependent. In contrast, nuclear localization of Tango is developmentally regulated; it is localized to the cytoplasm in most cells except the CNS midline, salivary duct, and tracheal cells where it accumulates in nuclei. Genetic and ectopic expression experiments indicate that Tango nuclear localization is dependent on the presence of a basic-helix-loop-helix-PAS protein such as Single-minded or Trachealess. Conversely, Drosophila cell culture experiments show that Single-minded and Trachealess nuclear localization is dependent on Tango since they are cytoplasmic in the absence of Tango. These results suggest a model in which Single-minded and Trachealess dimerize with Tango in the cytoplasm of the CNS midline cells and trachea, respectively, and the dimeric complex accumulates in nuclei in a ligand-independent mode and regulates lineage-specific transcription. The lineage-specific action of Single-minded and Trachealess derives from transcriptional activation of their genes in their respective lineages, not from extracellular signaling.

The bHLH-PAS transcriptional complex Sim:Tgo plays active roles in late oogenesis to promote follicle maturation and ovulation

“…The nuclear localization of Tgo coincides with the expression of Sim at stages 10B-12 and stage 14 (Fig 1B-E), which is consistent with our previous report (Knapp et al, 2020). Previous work showed that Tgo nuclear localization depends on Sim in CNS midline precursor cells (Ward et al, 1998). To test whether Sim is also required for Tgo nuclear localization in follicle cells, we examined the Tgo expression in sim -knockdown follicle cells.…”

“…Previous work showed that Tgo nuclear localization depends on Sim in CNS midline precursor cells (Ward et al, 1998). To test whether Sim is also required for Tgo nuclear localization in follicle cells, we examined the Tgo expression in sim-knockdown follicle cells.…”

“…Tgo can not only heterodimerize with Sim but also with other bHLH-PAS proteins including Trachealess and Spineless (Ohshiro and Saigo, 1997; Emmons et al, 1999). The process of dimerization is critical for Tgo nuclear localization (Ward et al, 1998), while the specific PAS domain confers the transcriptional specificity (Zelzer et al, 1997). Despite these studies, little is known about Sim and Tgo’s role in adult physiology and reproduction.…”

Transcriptional regulation of peripheral glial cell differentiation in the embryonic nervous system of drosophila

“…Although jaywalker has been described earlier (Salzberg et al, 1994), we suggest renaming the jaywalker alleles as tango alleles due to the extensive literature on tango (Crews, 1998). Tango encodes a PAS‐bHLH protein and is known to act as an interaction partner of the several other PAS‐bHLH proteins: Single Minded, which controls CNS midline formation, Trachealess, which controls tracheal development, and Sima, which controls hypoxic responses (Lavista‐Llanos et al, 2002; Ohshiro and Saigo, 1997; Ward et al, 1998).…”

“…6). In most cells, it is expressed within the cytoplasm and in only a few tissues, such as the trachea and the CNS midline, Tango is localized within the nucleus (Ward et al, 1998). In addition, some peripheral glial cells express nuclear Tango protein (see Fig.…”