Fork head and Sage maintain a uniform and patent salivary gland lumen through regulation of two downstream target genes, PH4alphaSG1 and PH4alphaSG2

Development. 2006 Sep;133(18):3517-27. doi: 10.1242/dev.02525. Epub 2006 Aug 16.

Abstract

(Fkh) is required to block salivary gland apoptosis, internalize salivary gland precursors, prevent expression of duct genes in secretory cells and maintain expression of CrebA, which is required for elevated secretory function. Here, we characterize two new Fkh-dependent genes: PH4alphaSG1 and PH4alphaSG2. We show through in vitro DNA-binding studies and in vivo expression assays that Fkh cooperates with the salivary gland-specific bHLH protein Sage to directly regulate expression of PH4alphaSG2, as well as sage itself, and to indirectly regulate expression of PH4alphaSG1. PH4alphaSG1 and PH4alphaSG2 encode alpha-subunits of resident ER enzymes that hydroxylate prolines in collagen and other secreted proteins. We demonstrate that salivary gland secretions are altered in embryos missing function of PH4alphaSG1 and PH4alphaSG2; secretory content is reduced and shows increased electron density by TEM. Interestingly, the altered secretory content results in regions of tube dilation and constriction, with intermittent tube closure. The regulation studies and phenotypic characterization of PH4alphaSG1 and PH4alphaSG2 link Fkh, which initiates tube formation, to the maintenance of an open and uniformly sized secretory tube.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / metabolism
  • Basic Helix-Loop-Helix Transcription Factors / physiology*
  • Cyclic AMP Response Element-Binding Protein A / genetics
  • Cyclic AMP Response Element-Binding Protein A / metabolism
  • Drosophila Proteins / analysis
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism*
  • Drosophila Proteins / physiology
  • Drosophila melanogaster / embryology
  • Drosophila melanogaster / genetics
  • Drosophila melanogaster / metabolism*
  • Electrophoretic Mobility Shift Assay
  • Forkhead Transcription Factors
  • Gene Expression Regulation, Developmental / genetics
  • Immunohistochemistry
  • In Situ Hybridization
  • Microscopy, Confocal
  • Microscopy, Electron, Transmission
  • Morphogenesis / genetics
  • Morphogenesis / physiology
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Nuclear Proteins / physiology*
  • Procollagen-Proline Dioxygenase / genetics
  • Procollagen-Proline Dioxygenase / metabolism
  • Salivary Glands / metabolism*
  • Salivary Glands / ultrastructure
  • Salivary Proteins and Peptides / genetics
  • Salivary Proteins and Peptides / metabolism
  • Salivary Proteins and Peptides / physiology*
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Transcription Factors / physiology*

Substances

  • Basic Helix-Loop-Helix Transcription Factors
  • Cyclic AMP Response Element-Binding Protein A
  • Drosophila Proteins
  • Forkhead Transcription Factors
  • Nuclear Proteins
  • Sage protein, Drosophila
  • Salivary Proteins and Peptides
  • Transcription Factors
  • fkh protein, Drosophila
  • Procollagen-Proline Dioxygenase