Cross-repressive Interactions Research Articles

A novel temporal identity window generates alternating Eve+/Nkx6+ motor neuron subtypes in a single progenitor lineage

BackgroundSpatial patterning specifies neural progenitor identity, with further diversity generated by temporal patterning within individual progenitor lineages. In vertebrates, these mechanisms generate “cardinal classes” of neurons that share a transcription factor identity and common morphology. In Drosophila, two cardinal classes are Even-skipped (Eve)+ motor neurons projecting to dorsal longitudinal muscles, and Nkx6+ motor neurons projecting to ventral oblique muscles. Cross-repressive interactions prevent stable double-positive motor neurons. The Drosophila neuroblast 7–1 (NB7–1) lineage uses a temporal transcription factor cascade to generate five distinct Eve+ motor neurons; the origin and development of Nkx6+ motor neurons remains unclear.MethodsWe use a neuroblast specific Gal4 line, sparse labelling and molecular markers to identify an Nkx6+ VO motor neuron produced by the NB7–1 lineage. We use lineage analysis to birth-date the VO motor neuron to the Kr+ Pdm+ neuroblast temporal identity window. We use gain- and loss-of-function strategies to test the role of Kr+ Pdm+ temporal identity and the Nkx6 transcription factor in specifying VO neuron identity.ResultsLineage analysis identifies an Nkx6+ neuron born from the Kr+ Pdm+ temporal identity window in the NB7–1 lineage, resulting in alternation of cardinal motor neuron subtypes within this lineage (Eve>Nkx6 > Eve). Co-overexpression of Kr/Pdm generates ectopic VO motor neurons within the NB7–1 lineage – the first evidence that this TTF combination specifies neuronal identity. Moreover, the Kr/Pdm combination promotes Nkx6 expression, which itself is necessary and sufficient for motor neuron targeting to ventral oblique muscles, thereby revealing a molecular specification pathway from temporal patterning to cardinal transcription factor expression to motor neuron target selection.ConclusionsWe show that one neuroblast lineage generates interleaved cardinal motor neurons fates; that the Kr/Pdm TTFs form a novel temporal identity window that promotes expression of Nkx6; and that the Kr/Pdm > Nkx6 pathway is necessary and sufficient to promote VO motor neuron targeting to the correct ventral muscle group.

Repressive interactions in gene regulatory networks: When you have no other choice.

Tightly regulated gene expression programs, orchestrated by complex interactions between transcription factors, control cell type specification during development. Repressive interactions play a critical role in these networks, facilitating decision-making between two or more alternative cell fates. Here, we use the ventral neural tube as an example to illustrate how cross repressive interactions within a network drive pattern formation and specify cell types in response to a graded patterning signal. This and other systems serve to highlight how external signals are integrated through the cis regulatory elements controlling key genes and provide insight into the molecular underpinning of the process. Even the simplest networks can lead to counterintuitive results and we argue that a combination of experimental dissection and modeling approaches will be necessary to fully understand network behavior and the underlying design principles. Studying these gene regulatory networks as a whole ultimately allows us to extract fundamental properties applicable across systems that can expand our mechanistic understanding of how organisms develop.

Proneural Genes Define Ground State Rules to Regulate Neurogenic Patterning and Cortical Folding

Transition from smooth, lissencephalic brains to highly-folded, gyrencephalic structures is associated with neuronal expansion and breaks in neurogenic symmetry. Here we show that Neurog2 and Ascl1 proneural genes regulate cortical progenitor cell differentiation through cross-repressive interactions to sustain neurogenic continuity in a lissencephalic rodent brain. Using in vivo lineage tracing, we found that Neurog2 and Ascl1 expression defines a lineage continuum of four progenitor pools, with ‘double+ progenitors’ having several unique features (least lineage-restricted, complex gene regulatory network, G 2 pausing). Strikingly, selective killing of double+ progenitors using split-Cre;Rosa-DTA transgenics breaks neurogenic symmetry by locally disrupting Notch signaling, leading to cortical folding. Finally, consistent with NEUROG2 and ASCL1 driving discontinuous neurogenesis and folding in gyrencephalic species, their transcripts are modular in folded macaque cortices and pseudo-folded human cerebral organoids. Neurog2/Ascl1 double + progenitors are thus Notch-ligand expressing ‘niche’ cells that control neurogenic periodicity to determine cortical gyrification.

An anterior signaling center patterns and sizes the anterior neuroectoderm of the sea urchin embryo.

Anterior signaling centers help specify and pattern the early anterior neuroectoderm (ANE) in many deuterostomes. In sea urchin the ANE is restricted to the anterior of the late blastula stage embryo, where it forms a simple neural territory comprising several types of neurons as well as the apical tuft. Here, we show that during early development, the sea urchin ANE territory separates into inner and outer regulatory domains that express the cardinal ANE transcriptional regulators FoxQ2 and Six3, respectively. FoxQ2 drives this patterning process, which is required to eliminate six3 expression from the inner domain and activate the expression of Dkk3 and sFRP1/5, two secreted Wnt modulators. Dkk3 and low expression levels of sFRP1/5 act additively to potentiate the Wnt/JNK signaling pathway governing the positioning of the ANE territory around the anterior pole, whereas high expression levels of sFRP1/5 antagonize Wnt/JNK signaling. sFRP1/5 and Dkk3 levels are rigidly maintained via autorepressive and cross-repressive interactions with Wnt signaling components and additional ANE transcription factors. Together, these data support a model in which FoxQ2 initiates an anterior patterning center that implements correct size and positions of ANE structures. Comparisons of functional and expression studies in sea urchin, hemichordate and chordate embryos reveal striking similarities among deuterostome ANE regulatory networks and the molecular mechanism that positions and defines ANE borders. These data strongly support the idea that the sea urchin embryo uses an ancient anterior patterning system that was present in the common ambulacrarian/chordate ancestor.

Prdm12 specifies V1 interneurons through cross-repressive interactions with Dbx1 and Nkx6 genes in Xenopus

V1 interneurons are inhibitory neurons that play an essential role in vertebrate locomotion. The molecular mechanisms underlying their genesis remain, however, largely undefined. Here, we show that the transcription factor Prdm12 is selectively expressed in p1 progenitors of the hindbrain and spinal cord in the frog embryo, and that a similar restricted expression profile is observed in the nerve cord of other vertebrates as well as of the cephalochordate amphioxus. Using frog, chick and mice, we analyzed the regulation of Prdm12 and found that its expression in the caudal neural tube is dependent on retinoic acid and Pax6, and that it is restricted to p1 progenitors, due to the repressive action of Dbx1 and Nkx6-1/2 expressed in the adjacent p0 and p2 domains. Functional studies in the frog, including genome-wide identification of its targets by RNA-seq and ChIP-Seq, reveal that vertebrate Prdm12 proteins act as a general determinant of V1 cell fate, at least in part, by directly repressing Dbx1 and Nkx6 genes. This probably occurs by recruiting the methyltransferase G9a, an activity that is not displayed by the amphioxus Prdm12 protein. Together, these findings indicate that Prdm12 promotes V1 interneurons through cross-repressive interactions with Dbx1 and Nkx6 genes, and suggest that this function might have only been acquired after the split of the vertebrate and cephalochordate lineages.

Sp8 plays a supplementary role to Pax6 in establishing the pMN/p3 domain boundary in the spinal cord.

Progenitor cells are segregated into multiple domains along the dorsoventral axis of the vertebrate neural tube, and each progenitor domain generates particular types of neurons. Selective cross-repressive interactions between pairs of class I and class II transcription factors play important roles in patterning neural progenitors into domains with clear boundaries. Here, we provide evidence that the zinc-finger protein Sp8 plays a supplementary role to Pax6 in establishing the pMN/p3 domain boundary through mutually repressive interactions with the class II protein Nkx2-2. The ventral limit of Sp8 expression is complementary to the dorsal limit of Nkx2-2 expression at the pMN/p3 boundary. Sp8 and Nkx2-2 exert cross-repressive interactions, and changing the expression of Sp8 and Nkx2-2 is coupled with pMN and p3 progenitor fate conversion. Sp8 exerts its neural patterning activities by acting as a transcriptional activator. The expression of a repressive form of Sp8 results in the selective inhibition of motor neuron generation and the ectopic induction of Nkx2-2 expression. Sp8 expression is positively regulated by, but not completely dependent on, Pax6. Furthermore, whereas loss of Pax6 function alone results in disruption of the pMN/p3 domain boundary only in the rostral levels of the spinal cord, loss of both Sp8 and Pax6 functions results in disruption of the pMN/p3 domain boundary along the whole rostrocaudal axis of the spinal cord. We conclude that Sp8 plays a supplementary role to Pax6 in specifying the pMN over p3 progenitor fate through cross-repressive interactions with Nkx2-2.

Antagonism between the Master Regulators of Differentiation Ensures the Discreteness and Robustness of Cell Fates

The discreteness of cell fates is an inherent and fundamental feature of multicellular organisms. Here we show that cross-antagonistic mechanisms of actions of MyoD and PPARγ, which are the master regulators of muscle and adipose differentiation, respectively, confer robustness to the integrity ofcell differentiation. Simultaneous expression of MyoD and PPARγ in mesenchymal stem/stromal cells led to the generation of a mixture of multinucleated myotubes and lipid-filled adipocytes. Interestingly, hybrid cells (i.e., lipid-filled myotubes) were not generated, suggesting that these differentiation programs are mutually exclusive. Mechanistically, although exogenously expressed MyoD was rapidly degraded in adipocytes through ubiquitin-proteasome pathways, exogenously expressed PPARγ was not downregulated in myotubes. In PPARγ-expressing myotubes, PPARγ-dependent histone hyperacetylation was inhibited in a subset of adipogenic gene loci, including that of C/EBPα, an essential effector of PPARγ. Thus, the cross-repressive interactions between MyoD- and PPARγ-induced differentiation programs ensure discrete cell-fate decisions.

MicroRNA input into a neural ultradian oscillator controls emergence and timing of alternative cell states

Progenitor maintenance, timed differentiation and the potential to enter quiescence are three fundamental processes that underlie the development of any organ system. In the nervous system, progenitor cells show short-period oscillations in the expression of the transcriptional repressor Hes1, while neurons and quiescent progenitors show stable low and high levels of Hes1, respectively. Here we use experimental data to develop a mathematical model of the double-negative interaction between Hes1 and a microRNA, miR-9, with the aim of understanding how cells transition from one state to another. We show that the input of miR-9 into the Hes1 oscillator tunes its oscillatory dynamics, and endows the system with bistability and the ability to measure time to differentiation. Our results suggest that a relatively simple and widespread network of cross-repressive interactions provides a unifying framework for progenitor maintenance, the timing of differentiation and the emergence of alternative cell states.

Cross-Repressive Interactions between SOC1 and the GATAs GNC and GNL/CGA1 in the Control of Greening, Cold Tolerance, and Flowering Time in Arabidopsis

The paralogous and functionally redundant GATA transcription factors GNC (for GATA, NITRATE-INDUCIBLE, CARBON-METABOLISM INVOLVED) and GNL/CGA1 (for GNC-LIKE/CYTOKININ-RESPONSIVE GATA FACTOR1) from Arabidopsis (Arabidopsis thaliana) promote greening and repress flowering downstream from the phytohormone gibberellin. The target genes of GNC and GNL with regard to flowering time control have not been identified as yet. Here, we show by genetic and molecular analysis that the two GATA factors act upstream from the flowering time regulator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) to directly repress SOC1 expression and thereby repress flowering. Interestingly, this analysis inversely also reveals that the MADS box transcription factor SOC1 directly represses GNC and GNL expression to control cold tolerance and greening, two further physiological processes that are under the control of SOC1. In summary, these findings support the case of a cross-repressive interaction between the GATA factors GNC and GNL and the MADS box transcription factor SOC1 in flowering time control on the one side and greening and cold tolerance on the other that may be governed by the various signaling inputs that are integrated at the level of SOC1 expression.

Genetic and Functional Modularity of Hox Activities in the Specification of Limb-Innervating Motor Neurons

A critical step in the assembly of the neural circuits that control tetrapod locomotion is the specification of the lateral motor column (LMC), a diverse motor neuron population targeting limb musculature. Hox6 paralog group genes have been implicated as key determinants of LMC fate at forelimb levels of the spinal cord, through their ability to promote expression of the LMC-restricted genes Foxp1 and Raldh2 and to suppress thoracic fates through exclusion of Hoxc9. The specific roles and mechanisms of Hox6 gene function in LMC neurons, however, are not known. We show that Hox6 genes are critical for diverse facets of LMC identity and define motifs required for their in vivo specificities. Although Hox6 genes are necessary for generating the appropriate number of LMC neurons, they are not absolutely required for the induction of forelimb LMC molecular determinants. In the absence of Hox6 activity, LMC identity appears to be preserved through a diverse array of Hox5–Hox8 paralogs, which are sufficient to reprogram thoracic motor neurons to an LMC fate. In contrast to the apparently permissive Hox inputs to early LMC gene programs, individual Hox genes, such as Hoxc6, have specific roles in promoting motor neuron pool diversity within the LMC. Dissection of motifs required for Hox in vivo specificities reveals that either cross-repressive interactions or cooperativity with Pbx cofactors are sufficient to induce LMC identity, with the N-terminus capable of promoting columnar, but not pool, identity when transferred to a heterologous homeodomain. These results indicate that Hox proteins orchestrate diverse aspects of cell fate specification through both the convergent regulation of gene programs regulated by many paralogs and also more restricted actions encoded through specificity determinants in the N-terminus.

Establishment of Motor Neuron-V3 Interneuron Progenitor Domain Boundary in Ventral Spinal Cord Requires Groucho-Mediated Transcriptional Corepression

BackgroundDorsoventral patterning of the developing spinal cord is important for the correct generation of spinal neuronal types. This process relies in part on cross-repressive interactions between specific transcription factors whose expression is regulated by Sonic hedgehog. Groucho/transducin-like Enhancer of split (TLE) proteins are transcriptional corepressors suggested to be recruited by at least certain Sonic hedgehog-controlled transcription factors to mediate the formation of spatially distinct progenitor domains within the ventral spinal cord. The aim of this study was to characterize the involvement of TLE in mechanisms regulating the establishment of the boundary between the most ventral spinal cord progenitor domains, termed pMN and p3. Because the pMN domain gives rise to somatic motor neurons while the p3 domain generates V3 interneurons, we also examined the involvement of TLE in the acquisition of these neuronal fates.Methodology and Principal FindingsA combination of in vivo loss- and gain-of-function studies in the developing chick spinal cord was performed to characterize the role of TLE in ventral progenitor domain formation. It is shown here that TLE overexpression causes increased numbers of p3 progenitors and promotes the V3 interneuron fate while suppressing the motor neuron fate. Conversely, dominant-inhibition of TLE increases the numbers of pMN progenitors and postmitotic motor neurons.ConclusionBased on these results, we propose that TLE is important to promote the formation of the p3 domain and subsequent generation of V3 interneurons.

Phosphorylation Regulates OLIG2 Cofactor Choice and the Motor Neuron-Oligodendrocyte Fate Switch

SummaryA fundamental feature of central nervous system development is that neurons are generated before glia. In the embryonic spinal cord, for example, a group of neuroepithelial stem cells (NSCs) generates motor neurons (MNs), before switching abruptly to oligodendrocyte precursors (OLPs). We asked how transcription factor OLIG2 participates in this MN-OLP fate switch. We found that Serine 147 in the helix-loop-helix domain of OLIG2 was phosphorylated during MN production and dephosphorylated at the onset of OLP genesis. Mutating Serine 147 to Alanine (S147A) abolished MN production without preventing OLP production in transgenic mice, chicks, or cultured P19 cells. We conclude that S147 phosphorylation, possibly by protein kinase A, is required for MN but not OLP genesis and propose that dephosphorylation triggers the MN-OLP switch. Wild-type OLIG2 forms stable homodimers, whereas mutant (unphosphorylated) OLIG2S147A prefers to form heterodimers with Neurogenin 2 or other bHLH partners, suggesting a molecular basis for the switch.

Mir-17-3p Controls Spinal Neural Progenitor Patterning by Regulating Olig2/Irx3 Cross-Repressive Loop

Neural patterning relies on transcriptional cross-repressive interactions that ensure unequivocal assignment of neural progenitor identity to proliferating cells. Progenitors of spinal motor neurons (pMN) and V2 interneurons (p2) are specified by a pair of cross-repressive transcription factors, Olig2 and Irx3. Lineage tracing revealed that many p2 progenitors transiently express the pMN marker Olig2 during spinal cord development. Here we demonstrate that the repression of Olig2 in p2 domain is controlled by mir-17-3p microRNA-mediated silencing of Olig2 mRNA. Mice lacking all microRNAs or just the mir-17∼92 cluster manifest a dorsal shift in pMN/p2 boundary and impairment in the production of V2 interneurons. Our findings suggest that microRNA-mediated repression of Olig2 mRNA plays a critical role during the patterning of ventral spinal progenitor domains by shifting the balance of cross-repressive interactions between Olig2 and Irx3 transcription factors.

Functional Diversity of ESC-Derived Motor Neuron Subtypes Revealed through Intraspinal Transplantation

Cultured ESCs can form different classes of neurons, but whether these neurons can acquire specialized subtype features typical of neurons in vivo remains unclear. We show here that mouse ESCs can be directed to form highly specific motor neuron subtypes in the absence of added factors, through a differentiation program that relies on endogenous Wnts, FGFs, and Hh-mimicking the normal program of motor neuron subtype differentiation. Molecular markers that characterize motor neuron subtypes anticipate the functional properties of these neurons in vivo: ESC-derived motor neurons grafted isochronically into chick spinal cord settle in appropriate columnar domains and select axonal trajectories with a fidelity that matches that of their in vivo generated counterparts. ESC-derived motor neurons can therefore be programmed in a predictive manner to acquire molecular and functional properties that characterize one of the many dozens of specialized motor neuron subtypes that exist in vivo.

Conserved and novel roles for the Gsh2 transcription factor in primary neurogenesis

The Gsx genes encode members of the ParaHox family of homeodomain transcription factors, which are expressed in the developing central nervous system in members of all major groups of bilaterians. The Gsx genes in Xenopus show similar patterns of expression to their mammalian homologues during late development. However, they are also expressed from early neurula stages in an intermediate region of the open neural plate where primary interneurons form. The Gsx homologue in the protostome Drosophila is expressed in a corresponding intermediate region of the embryonic neuroectoderm, and is essential for the correct specification of the neuroblasts that arise from it, suggesting that Gsx genes may have played a role in intermediate neural specification in the last common bilaterian ancestor. Here, we show that manipulation of Gsx function disrupts the differentiation of primary interneurons. We demonstrate that, despite their similar expression patterns, the uni-directional system of interactions between homeodomain transcription factors from the Msx, Nkx and Gsx families in the Drosophila neuroectoderm is not conserved between their homologues in the Xenopus open neural plate. Finally, we report the identification of Dbx1 as a direct target of Gsh2-mediated transcriptional repression, and show that a series of cross-repressive interactions, reminiscent of those that exist in the amniote neural tube, act between Gsx, Dbx and Nkx transcription factors to pattern the medial aspect of the central nervous system at open neural plate stages in Xenopus.

Nkx6 Transcription Factors and Ptf1a Function as Antagonistic Lineage Determinants in Multipotent Pancreatic Progenitors

The molecular mechanisms that underlie cell lineage diversification of multipotent progenitors in the pancreas are virtually unknown. Here we show that the early fate choice of pancreatic progenitors between the endocrine and acinar cell lineage is restricted by cross-repressive interactions between the transcription factors Nkx6.1/Nkx6.2 (Nkx6) and Ptf1a. Using genetic loss- and gain-of-function approaches, we demonstrate that Nkx6 factors and Ptf1a are required and sufficient to repress the alternative lineage program and to specify progenitors toward an endocrine or acinar fate, respectively. The Nkx6/Ptf1a switch only operates during a critical competence window when progenitors are still multipotent and can be uncoupled from cell differentiation. Thus, cross-antagonism between Nkx6 and Ptf1a in multipotent progenitors governs the equilibrium between endocrine and acinar cell neogenesis required for normal pancreas development.

Dbxmediates neuronal specification and differentiation through cross-repressive, lineage-specific interactions witheveandhb9

Individual neurons adopt and maintain defined morphological and physiological phenotypes as a result of the expression of specific combinations of transcription factors. In particular, homeodomain-containing transcription factors play key roles in determining neuronal subtype identity in flies and vertebrates. dbx belongs to the highly divergent H2.0 family of homeobox genes. In vertebrates, Dbx1 and Dbx2 promote the development of a subset of interneurons, some of which help mediate left-right coordination of locomotor activity. Here, we identify and show that the single Drosophila ortholog of Dbx1/2 contributes to the development of specific subsets of interneurons via cross-repressive, lineage-specific interactions with the motoneuron-promoting factors eve and hb9 (exex). dbx is expressed primarily in interneurons of the embryonic, larval and adult central nervous system, and these interneurons tend to extend short axons and be GABAergic. Interestingly, many Dbx(+) interneurons share a sibling relationship with Eve(+) or Hb9(+) motoneurons. The non-overlapping expression of dbx and eve, or dbx and hb9, within pairs of sibling neurons is initially established as a result of Notch/Numb-mediated asymmetric divisions. Cross-repressive interactions between dbx and eve, and dbx and hb9, then help maintain the distinct expression profiles of these genes in their respective pairs of sibling neurons. Strict maintenance of the mutually exclusive expression of dbx relative to that of eve and hb9 in sibling neurons is crucial for proper neuronal specification, as misexpression of dbx in motoneurons dramatically hinders motor axon outgrowth.

Spatially distinct functions of PAX6 and NKX2.2 during gliogenesis in the ventral spinal cord

During ventral spinal cord (vSC) development, the p3 and pMN progenitor domain boundary is thought to be maintained by cross-repressive interactions between NKX2.2 and PAX6. Using loss-of-function analysis during the neuron-glial fate switch we show that the identity of the p3 domain is not maintained by the repressive function of NKX2.2 on Pax6 expression, even in the absence of NKX2.9. We further show that NKX2.2 is necessary to induce the expression of Slit1 and Sulfatase 1 (Sulf1) in the vSC in a PAX6-independent manner. Conversely, we show that PAX6 regulates Sulf1/Slit1 expression in the vSC in an NKX2.2/NKX6.1-independent manner. Consequently, deregulation of Sulf1 expression in Pax6-mutant embryos has stage-specific implications on neural patterning, associated with enhancement of Sonic Hedgehog activity. On the other hand, deregulation of Slit1 expression in gliogenic neural progenitors leads to changes in Astrocyte subtype identity. These data provide important insights into specific functions of PAX6 and NKX2.2 during glial cell specification that have so far remained largely unexplored.

Cross-repressive interactions betweenLrig3and netrin 1 shape the architecture of the inner ear

The sense of balance depends on the intricate architecture of the inner ear, which contains three semicircular canals used to detect motion of the head in space. Changes in the shape of even one canal cause drastic behavioral deficits, highlighting the need to understand the cellular and molecular events that ensure perfect formation of this precise structure. During development, the canals are sculpted from pouches that grow out of a simple ball of epithelium, the otic vesicle. A key event is the fusion of two opposing epithelial walls in the center of each pouch, thereby creating a hollow canal. During the course of a gene trap mutagenesis screen to find new genes required for canal morphogenesis, we discovered that the Ig superfamily protein Lrig3 is necessary for lateral canal development. We show that this phenotype is due to ectopic expression of the axon guidance molecule netrin 1 (Ntn1), which regulates basal lamina integrity in the fusion plate. Through a series of genetic experiments, we show that mutually antagonistic interactions between Lrig3 and Ntn1 create complementary expression domains that define the future shape of the lateral canal. Remarkably, removal of one copy of Ntn1 from Lrig3 mutants rescues both the circling behavior and the canal malformation. Thus, the Lrig3/Ntn1 feedback loop dictates when and where basement membrane breakdown occurs during canal development, revealing a new mechanism of complex tissue morphogenesis.

Corl1, a Novel Neuronal Lineage-specific Transcriptional Corepressor for the Homeodomain Transcription Factor Lbx1

During development, neuronal identity is determined by a combination of numerous transcription factors. However, the mechanisms of synergistic action of these factors in transcriptional regulation and subsequent cell fate specification are largely unknown. In this study, we identified a novel gene, Corl1, encoding a nuclear protein with homology to the Ski oncoprotein. Corl1 was highly selectively expressed in the central nervous system (CNS). In the embryonic CNS, Corl1 was expressed in a certain subset of postmitotic neurons generated posterior to the midbrain-hindbrain border. In the developing spinal cord, Corl1 was selectively expressed in the dorsal horn interneurons where a homeodomain transcription factor, Lbx1, is required for proper specification. Corl1 was localized in a nuclear dot-like structure and interacted with general transcriptional corepressors. In addition, Corl1 showed transcriptional repression activity in the GAL4-fusion system, indicating its involvement in the regulation of transcriptional repression. Furthermore, Corl1 interacted with Lbx1 and cooperatively repressed transcription, suggesting that it acts as a transcriptional corepressor for Lbx1 in regulating cell fate determination in the dorsal spinal cord. Corl1 corepressor activity did not depend on Gro/TLE activity, and Gro/TLE also functioned as a corepressor for Lbx1. Thus, Lbx1 can select two independent partners, Corl1 and Gro/TLE, as corepressors. Identification of a novel transcriptional corepressor with neuronal subtype-restricted expression might provide insights into the mechanisms of cell fate determination in neurons.