Drosophila JAK/STAT pathway reveals distinct initiation and reinforcement steps in early transcription of Sxl.
X-linked signal elements (XSEs) communicate the dose of X chromosomes to the regulatory-switch gene Sex-lethal (Sxl) during Drosophila sex determination. Unequal XSE expression in precellular XX and XY nuclei ensures that only XX embryos will activate the establishment promoter, SxlPe, to produce a pulse of the RNA-binding protein, SXL [1]. Once XSE protein concentrations have been assessed, SxlPe is inactivated and the maintenance promoter, SxlPm, is turned on in both sexes; however, only in females is SXL present to direct the SxlPm-derived transcripts to be spliced into functional mRNA [2, 3]. Thereafter, Sxl is maintained in the on state by positive autoregulatory RNA splicing [2]. Once set in the stable on (female) or off (male) state, Sxl controls somatic sexual development through control of downstream effectors of sexual differentiation and dosage compensation [1, 4]. Most XSEs encode transcription factors that bind SxlPe, but the XSE unpaired (upd) encodes a secreted ligand for the JAK/STAT pathway [5-7]. We show that although STAT directly regulates SxlPe, it is dispensable for promoter activation. Instead, JAK/STAT is needed to maintain high-level SxlPe expression in order to ensure Sxl autoregulation in XX embryos. Thus, upd is a unique XSE that augments, rather than defines, the initial sex-determination signal.
Avila
Frank W
FW
Department of Biology, Texas A&M University, 3258 TAMU, College Station, TX 77843, USA.
Erickson
James W
JW
D000818:Animals; D004330:Drosophila / Q000196:embryology* / Q000235:genetics / Q000378:metabolism; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000378:metabolism; D005260:Female; D018507:Gene Expression Regulation, Developmental; D053612:Janus Kinases / Q000378:metabolism*; D008297:Male; D016601:RNA-Binding Proteins / Q000235:genetics*; D050791:STAT Transcription Factors / Q000378:metabolism*; D019849:Sex Determination Processes; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014960:X Chromosome
D029721:Drosophila Proteins; D016601:RNA-Binding Proteins; D050791:STAT Transcription Factors; C067777:Sxl protein, Drosophila; D014157:Transcription Factors; C115570:upd1 protein, Drosophila; D053612:Janus Kinases; C085845:hop protein, Drosophila