Suchergebnisse

25 páginas, 8 figuras. ; During development, signal-regulated transcription factors (TFs) act as basal repressors and upon signalling through morphogens or cell-to-cell signalling shift to activators, mediating precise and transient responses. Conversely, at the final steps of neuron specification, terminal selector TFs directly initiate and maintain neuron-type specific gene expression through enduring functions as activators. C. elegans contains 3 types of serotonin synthesising neurons that share the expression of the serotonin biosynthesis pathway genes but not of other effector genes. Here, we find an unconventional role for LAG-1, the signal-regulated TF mediator of the Notch pathway, as terminal selector for the ADF serotonergic chemosensory neuron, but not for other serotonergic neuron types. Regulatory regions of ADF effector genes contain functional LAG-1 binding sites that mediate activation but not basal repression. lag-1 mutants show broad defects in ADF effector genes activation, and LAG-1 is required to maintain ADF cell fate and functions throughout life. Unexpectedly, contrary to reported basal repression state for LAG-1 prior to Notch receptor activation, gene expression activation in the ADF neuron by LAG-1 does not require Notch signalling, demonstrating a default activator state for LAG-1 independent of Notch. We hypothesise that the enduring activity of terminal selectors on target genes required uncoupling LAG-1 activating role from receiving the transient Notch signalling. ; NF research is funded by European ResearcPRE2018-086h Council (ERC StG 281920; ERC COG 101002203), Spanish Government (SAF2017-84790-R) and Generalitat Valenciana (PROMETEO/2018/055). A.M.T holds the PRE2018-086632 fellowship from Spanish Government and A.J the ACIF/2015/398 fellowship from Generalitat Valenciana. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. ; Peer reviewed

14 páginas, 8 figuras, 1 tabla. Material suplementario accesible online. ; Transcription factors that drive neuron type-specific terminal differentiation programs in the developing nervous system are often expressed in several distinct neuronal cell types, but to what extent they have similar or distinct activities in individual neuronal cell types is generally not well explored. We investigate this problem using, as a starting point, the C. elegans LIM homeodomain transcription factor ttx-3, which acts as a terminal selector to drive the terminal differentiation program of the cholinergic AIY interneuron class. Using a panel of different terminal differentiation markers, including neurotransmitter synthesizing enzymes, neurotransmitter receptors and neuropeptides, we show that ttx-3 also controls the terminal differentiation program of two additional, distinct neuron types, namely the cholinergic AIA interneurons and the serotonergic NSM neurons. We show that the type of differentiation program that is controlled by ttx-3 in different neuron types is specified by a distinct set of collaborating transcription factors. One of the collaborating transcription factors is the POU homeobox gene unc-86, which collaborates with ttx-3 to determine the identity of the serotonergic NSM neurons. unc-86 in turn operates independently of ttx-3 in the anterior ganglion where it collaborates with the ARID-type transcription factor cfi-1 to determine the cholinergic identity of the IL2 sensory and URA motor neurons. In conclusion, transcription factors operate as terminal selectors in distinct combinations in different neuron types, defining neuron type-specific identity features. ; This work was funded by the National Institutes of Health [R01NS039996-05 and R01NS050266-03 to O.H.; R01NS076558 to D.A.C.-R.; and R01NS070644 to R.S.M.]; a March of Dimes Foundation Grant (to D.A.C.-R.); the Spanish Government [SAF2011-26273 to N.F.]; a Marie Curie Career Integration Grant (to N.F.); a VAL i+d Fellowship from Generalitat Valenciana (to C.L.-F.); and a European Research Council Starting Grant (to N.F.). N.F. is a National Alliance for Research on Schizophrenia and Depression (NARSAD) Young Investigator. O.H. is an Investigator of the Howard Hughes Medical Institute. Deposited in PMC for release after 6 months. ; Peer reviewed