STAT3 promotes motor neuron differentiation by collaborating with motor neuron-specific LIM complex

Abstract

The motor neuron (MN)-hexamer complex consisting of LIM homeobox 3, Islet-1, and nuclear LIM interactor is a key determinant of motor neuron specification and differentiation. To gain insights into the transcriptional network in motor neuron development, we performed a genome-wide ChIP-sequencing analysis and found that the MN-hexamer directly regulates a wide array of motor neuron genes by binding to the HxRE (hexamer response element) shared among the target genes. Interestingly, STAT3-binding motif is highly enriched in the MN-hexamer-bound peaks in addition to the HxRE. We also found that a transcriptionally active form of STAT3 is expressed in embryonic motor neurons and that STAT3 associates with the MN-hexamer, enhancing the transcriptional activity of the MN-hexamer in an upstream signal-dependent manner. Correspondingly, STAT3 was needed for motor neuron differentiation in the developing spinal cord. Together, our studies uncover crucial gene regulatory mechanisms that couple MN-hexamer and STAT-activating extracellular signals to promote motor neuron differentiation in vertebrate spinal cord.he combinatorial action of transcription factors is a prevalent strategy for achieving cellular complexity in the CNS. However, how the combinatorial action of transcription factors leads to the expression of distinct batteries of terminal differentiation genes, which together establish a specific cellular identity; how the cell fate-specifying transcription factors interact with extracellular cues remain unclear. To address these questions, it is essential to identify both the cis-regulatory elements in the genome, which recruit a specific combination of transcription factors, and the target genes associated with those cis-regulatory elements.One of the best examples of combinatorial transcription codes has emerged from studies of spinal motor neuron (MN) development (1). Two LIM-homeodomain (LIM-HD) factors, LIM homeobox 3 (Lhx3) and Islet-1 (Isl1), are vital for directing MN fate specification in the developing spinal cord (2-5). During this process, two Isl1:Lhx3 dimers bind to nuclear LIM interactor (NLI, also known as LDB for LIM domain binding) that has a self-dimerization domain, thereby forming the MN-hexamer complex ( Fig. 1A and Fig. S1A) (2, 6). The combinatorial expression of Lhx3 and Isl1 is capable of triggering MN specification in chick spinal cord, ES cells (ESCs), and induced pluripotent stem cells (2,(6)(7)(8). In contrast to MNs, during the specification of V2 interneurons, two Lhx3s and two NLIs form a tetrameric complex, which directs the V2-interneuron fate (Fig. S1A) (2, 9). Thus, the combinatorial action of Lhx3 and Isl1, via the formation of the MN-hexamer, is critical to determine MN identity over V2-interneuron fate. However, key questions remain unanswered. First, does the MN-hexamer directly control terminal differentiation genes that are required for consolidating the functional identity of MNs? Second, does the MN-hexamer collaborate with other transcription factors and/or extracellu...

Effects of STAT3 inhibitors on neural functional recovery after spinal cord injury in rats

“…The STAT3 inhibitor significantly upregulated the expression of NF-200 and β-tubulin ш. A study has reported that IL-6 and the activity of its signaling partner establish a positive feedback mechanism with PAR1 that may promote IL-6-STAT3 signaling to levels sufficient to elicit fulminant astrogliosis, including increases in levels of the astroglial intermediate filament proteins GFAP and vimentin (18,19) In contrast to the current study, other studies have reported that STAT3 promotes motor neuron differentiation by collaborating with a motor neuronspecific LIM complex (21). STAT3 performs different roles during neural stem cell maintenance and motor neuron differentiation.…”

Identification of STAM1 as a novel effector of ventral projection of spinal motor neurons

“…These studies, combined with MN transcriptome analyses (Lee et al, 2012;Mazzoni et al, 2013), revealed that the ISL1-LHX3 complex directly regulates the expression of a wide range of downstream effector genes that function not only in cell fate specification but also in subsequent maturation steps of MN differentiation, such as cell migration, axon pathfinding and synapse formation. As a result, the roles of individual target genes of the ISL1-LHX3 complex in MN specification and differentiation/maturation have finally begun to be dissected (Cho et al, 2014;Lee et al, 2012Lee et al, , 2013Mazzoni et al, 2013). Interestingly, v-MNs in embryos deficient in both LHX3 and LHX4 reorients their axonal projections dorsally, whereas the misexpression of LHX3 in d-MNs reorients their axonal projections ventrally (Sharma et al, 1998).…”

“…LIM homeobox 3 (LHX3) and Islet 1 (ISL1), two LIMhomeodomain (LIM-HD) factors, play crucial roles in directing MN fate specification and differentiation in developing spinal cord (Lee et al, 2013;Pfaff et al, 1996;Sharma et al, 1998;Tanabe et al, 1998;Thaler et al, 2002). During these processes, two ISL1: LHX3 dimers bind to nuclear LIM interactor (NLI; also known as LDB for LIM-domain binding), which has a self-dimerization domain, and form a hexameric complex, named the ISL1-LHX3 complex ( Fig.…”

“…1A) (Lee et al, 2013). To understand better the role of the ISL1-LHX3 complex in spinal MN specification and differentiation, a genome-wide mapping of ISL1-LHX3 complexbinding sites has been recently performed using chromatin immunoprecipitation sequencing (ChIP-seq) (Lee et al, 2013;Mazzoni et al, 2013). These studies, combined with MN transcriptome analyses (Lee et al, 2012;Mazzoni et al, 2013), revealed that the ISL1-LHX3 complex directly regulates the expression of a wide range of downstream effector genes that function not only in cell fate specification but also in subsequent maturation steps of MN differentiation, such as cell migration, axon pathfinding and synapse formation.…”

“…During these processes, two ISL1: LHX3 dimers bind to nuclear LIM interactor (NLI; also known as LDB for LIM-domain binding), which has a self-dimerization domain, and form a hexameric complex, named the ISL1-LHX3 complex ( Fig. 1A) (Lee et al, 2013). To understand better the role of the ISL1-LHX3 complex in spinal MN specification and differentiation, a genome-wide mapping of ISL1-LHX3 complexbinding sites has been recently performed using chromatin immunoprecipitation sequencing (ChIP-seq) (Lee et al, 2013;Mazzoni et al, 2013).…”