title: Muscle cell fate choice requires the T-box transcription factor midline in Drosophila.
abstract: Drosophila Midline (Mid) is an ortholog of vertebrate Tbx20, which plays roles in the developing heart, migrating cranial motor neurons, and endothelial cells. Mid functions in cell-fate specification and differentiation of tissues that include the ectoderm, cardioblasts, neuroblasts, and egg chambers; however, a role in the somatic musculature has not been described. We identified mid in genetic and molecular screens for factors contributing to somatic muscle morphogenesis. Mid is expressed in founder cells (FCs) for several muscle fibers, and functions cooperatively with the T-box protein H15 in lateral oblique muscle 1 and the segment border muscle. Mid is particularly important for the specification and development of the lateral transverse (LT) muscles LT3 and LT4, which arise by asymmetric division of a single muscle progenitor. Mid is expressed in this progenitor and its two sibling FCs, but is maintained only in the LT4 FC. Both muscles were frequently missing in mid mutant embryos, and LT4-associated expression of the transcription factor Krüppel (Kr) was lost. When present, LT4 adopted an LT3-like morphology. Coordinately, mid misexpression caused LT3 to adopt an LT4-like morphology and was associated with ectopic Kr expression. From these data, we concluded that mid functions first in the progenitor to direct development of LT3 and LT4, and later in the FCs to influence whichever of these differentiation profiles is selected. Mid is the first T-box factor shown to influence LT3 and LT4 muscle identity and, along with the T-box protein Optomotor-blind-related-gene 1 (Org-1), is representative of a new class of transcription factors in muscle specification.
authors.affiliation: Stowers Institute for Medical Research, Kansas City, Missouri 64110.
authors.forename: Ram P
authors.initials: RP
authors.lastname: Kumar
authors.affiliation: Program in Developmental Biology, Memorial Sloan Kettering Cancer Center, New York, New York 10065.
authors.forename: Krista C
authors.initials: KC
authors.lastname: Dobi
authors.affiliation: Program in Developmental Biology, Memorial Sloan Kettering Cancer Center, New York, New York 10065.
authors.forename: Mary K
authors.initials: MK
authors.lastname: Baylies
authors.affiliation: Stowers Institute for Medical Research, Kansas City, Missouri 64110 Department of Anatomy and Cell Biology, University of Kansas School of Medicine, Kansas City, Kansas 66160 sma@stowers.org.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Abmayr
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000235:genetics; D004330:Drosophila / Q000196:embryology / Q000235:genetics*; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D051741:Kruppel-Like Transcription Factors / Q000378:metabolism; D024510:Muscle Development / Q000235:genetics*; D009928:Organ Specificity; D020825:T-Box Domain Proteins / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics
chemical_list: D029721:Drosophila Proteins; C495572:H15 protein, Drosophila; C497244:Kr protein, Drosophila; D051741:Kruppel-Like Transcription Factors; D020825:T-Box Domain Proteins; D014157:Transcription Factors; C495571:mid protein, Drosophila
keywords: Tbx20; differentiation; founder cell; midline; muscle identity