1,721,079 research outputs found
motoneuron identity by the combinatorial action of POU and LIM-HD factors
No full textIn both vertebrates and invertebrates, members of the LIM-homeodomain (LIM-HD) family of transcription factors act in combinatorial codes to specify motoneuron subclass identities. In the developing Drosophila embryo, the LIM-HD factors Islet (Tailup) and Lim3, specify the set of motoneuron subclasses that innervate ventral muscle targets. However, as several subclasses express both Islet and Lim3, this combinatorial code alone cannot explain how these motoneuron groups are further differentiated. To identify additional factors that may act to refine this LIM-HD code, we have analyzed the expression of POU genes in the Drosophila embryonic nerve cord. We find that the class III POU protein, Drifter (Ventral veinless), is co-expressed with Islet and Lim3 specifically in the ISNb motoneuron subclass. Loss-of-function and misexpression studies demonstrate that the LIM-HD combinatorial code requires Drifter to confer target specificity between the ISNb and TN motoneuron subclasses. To begin to elucidate molecules downstream of the LIM-HD code, we examined the involvement of the Beaten path (Beat) family of immunoglobulin-containing cell-adhesion molecules. We find that beat Ic genetically interacts with islet and Lim3 in the TN motoneuron subclass and can also rescue the TN fasciculation defects observed in islet and Lim3 mutants. These results suggest that in the TN motoneuron context, Islet and Lim3 may specify axon target selection through the actions of IgSF call-adhesion molecules.</p
Transcriptional control of axonal guidance and sorting in dorsal interneurons by the Lim-HD proteins Lhx9 and Lhx1
No full textAbstract Background Lim-HD proteins control crucial aspects of neuronal differentiation, including subtype identity and axonal guidance. The Lim-HD proteins Lhx2/9 and Lhx1/5 are expressed in the dorsal spinal interneuron populations dI1 and dI2, respectively. While they are not required for cell fate acquisition, their role in patterning the axonal trajectory of dI1 and dI2 neurons remains incompletely understood. Results Using newly identified dI1- and dI2-specific enhancers to trace axonal trajectories originating from these interneurons, we found that each population is subdivided into several distinct groups according to their axonal pathways. dI1 neurons project axons rostrally, either ipsi- or contra-laterally, while dI2 are mostly commissural neurons that project their axons rostrally and caudally. The longitudinal axonal tracks of each neuronal population self-fasciculate to form dI1- and dI2-specific bundles. The dI1 bundles are spatially located ventral relative to dI2 bundles. To examine the functional contribution of Lim-HD proteins to establishment of dI axonal projections, the Lim-HD code of dI neurons was altered by cell-specific ectopic expression. Expression of Lhx1 in dI1 neurons caused a repression of Lhx2/9 and imposed caudal projection to the caudal commissural dI1 neurons. Complementarily, when expressed in dI2 neurons, Lhx9 repressed Lhx1/5 and triggered a bias toward rostral projection in otherwise caudally projecting dI2 neurons, and ventral shift of the longitudinal axonal fascicule. Conclusion The Lim-HD proteins Lhx9 and Lhx1 serve as a binary switch in controlling the rostral versus caudal longitudinal turning of the caudal commissural axons. Lhx1 determines caudal turning and Lhx9 triggers rostral turning.</p
Seizure evoked regulation of LIM-HD genes and co-factors in the postnatal and adult hippocampus [v1; ref status: indexed, http://f1000r.es/1d0]
No full textThe LIM-homeodomain (LIM-HD) family of transcription factors is well known for its functions during several developmental processes including cell fate specification, cell migration and axon guidance, and its members play fundamental roles in hippocampal development. The hippocampus is a structure that displays striking activity dependent plasticity. We examined whether LIM-HD genes and their co-factors are regulated during kainic acid induced seizure in the adult rat hippocampus as well as in early postnatal rats, when the hippocampal circuitry is not fully developed. We report a distinct and field-specific regulation of LIM-HD genes Lhx1, Lhx2, and Lhx9, LIM-only gene Lmo4, and cofactor Clim1a in the adult hippocampus after seizure induction. In contrast none of these genes displayed altered levels upon induction of seizure in postnatal animals. Our results provide evidence of temporal and spatial seizure mediated regulation of LIM-HD family members and suggest that LIM-HD gene function may be involved in activity dependent plasticity in the adult hippocampu
Together at Last bHLH and LIM-HD Regulators Cooperate to Specify Motor Neurons
No full textAbstractbHLH and LIM-HD transcription factors were originally thought to act at different stages of neurogenesis: bHLHs as neuronal “inducers” and LIM-HDs as postmitotic subtype determinants. These distinctions are becoming blurred, and a current study by Lee and Pfaff in this issue of Neuron shows that interaction between these factors functions to synchronize neurogenesis with neuronal cell type specification
tailup, a LIM-HD gene, and Iro-C cooperate in Drosophila dorsal mesothorax specification
No full textThe LIM-HD gene tailup (tup; also known as islet) has been categorised as a prepattern gene that antagonises the formation of sensory bristles on the notum of Drosophila by downregulating the expression of the proneural achaete-scute genes. Here we show that tup has an earlier function in the development of the imaginal wing disc; namely, the specification of the notum territory. Absence of tup function causes cells of this anlage to upregulate different wing-hinge genes and to lose expression of some notum genes. Consistently, these cells differentiate hinge structures or modified notum cuticle. The LIM-HD co-factors Chip and Ssdp are also necessary for notum specification. This suggests that Tup acts in this process in a complex with Chip and Ssdp. Overexpression of tup, together with araucan, a `pronotum' gene of the iroquois complex (Iro-C), synergistically reinforces the weak capacity of either gene, when overexpressed singly, to induce ectopic notum-like development. Whereas the Iro-C genes are activated in the notum anlage by EGFR signalling, tup is positively regulated by Dpp signalling. Our data support a model in which the EGFR and Dpp signalling pathways, with their respective downstream Iro-C and tup genes, converge and cooperate to commit cells to the notum developmental fate
Supplementary figure S1-S11 captions from LIM-HD transcription factors control axial patterning and specify distinct neuronal and intestinal cell identities in planarians
No full textAdult planarians can regenerate the gut, eyes and even a functional brain. Proper identity and patterning of the newly formed structures require signals that guide and commit their adult stem cells. During embryogenesis, LIM-Homeodomain (LIM-HD) transcription factors act in a combinatorial ‘LIM code’ to control cell fate determination and differentiation. However, our understanding about the role these genes play during regeneration and homeostasis is limited. Here, we report the full repertoire of LIM-HD genes in Schmidtea mediterranea. We found that lim homeobox genes (lhx) appear expressed in complementary patterns along the cephalic ganglia and digestive system of the planarian, with some of them being co-expressed in the same cell types. We have identified that Smed-islet1, -lhx1/5-1, -lhx2/9-3, -lhx6/8, -lmx1a/b-2 and -lmx1a/b-3 are essential to pattern and size the planarian brain as well as for correct regeneration of specific subpopulations of dopaminergic, serotonergic, GABAergic and cholinergic neurons, while Smed-lhx1/5.2 and -lhx2/9.2 are required for the proper expression of intestinal cell type markers, specifically the goblet subtype. LIM-HD are also involved in controlling axonal pathfinding (lhx6/8), axial patterning (islet1, lhx1/5-1, lmx1a/b-3), head/body proportions (islet2) and stem cell proliferation (lhx3/4, lhx2/9-3, lmx1a/b-2, lmx1a/b-3). Altogether, our results suggest that planarians might present a combinatorial LIM code that controls axial patterning, axonal growing and specify distinct neuronal and intestinal cell identities
<it>In vivo </it>imaging of cell behaviors and F-actin reveals LIM-HD transcription factor regulation of peripheral versus central sensory axon development
Full text linkAbstract Background Development of specific neuronal morphology requires precise control over cell motility processes, including axon formation, outgrowth and branching. Dynamic remodeling of the filamentous actin (F-actin) cytoskeleton is critical for these processes; however, little is known about the mechanisms controlling motile axon behaviors and F-actin dynamics in vivo. Neuronal structure is specified in part by intrinsic transcription factor activity, yet the molecular and cellular steps between transcription and axon behavior are not well understood. Zebrafish Rohon-Beard (RB) sensory neurons have a unique morphology, with central axons that extend in the spinal cord and a peripheral axon that innervates the skin. LIM homeodomain (LIM-HD) transcription factor activity is required for formation of peripheral RB axons. To understand how neuronal morphogenesis is controlled in vivo and how LIM-HD transcription factor activity differentially regulates peripheral versus central axons, we used live imaging of axon behavior and F-actin distribution in vivo. Results We used an F-actin biosensor containing the actin-binding domain of utrophin to characterize actin rearrangements during specific developmental processes in vivo, including axon initiation, consolidation and branching. We found that peripheral axons initiate from a specific cellular compartment and that F-actin accumulation and protrusive activity precede peripheral axon initiation. Moreover, disruption of LIM-HD transcriptional activity has different effects on the motility of peripheral versus central axons; it inhibits peripheral axon initiation, growth and branching, while increasing the growth rate of central axons. Our imaging revealed that LIM-HD transcription factor activity is not required for F-actin based protrusive activity or F-actin accumulation during peripheral axon initiation, but can affect positioning of F-actin accumulation and axon formation. Conclusion Our ability to image the dynamics of F-actin distribution during neuronal morphogenesis in vivo is unprecedented, and our experiments provide insight into the regulation of cell motility as neurons develop in the intact embryo. We identify specific motile cell behaviors affected by LIM-HD transcription factor activity and reveal how transcription factors differentially control the formation and growth of two axons from the same neuron.</p
Supplementary figures S1-S11 from LIM-HD transcription factors control axial patterning and specify distinct neuronal and intestinal cell identities in planarians
No full textAdult planarians can regenerate the gut, eyes and even a functional brain. Proper identity and patterning of the newly formed structures require signals that guide and commit their adult stem cells. During embryogenesis, LIM-Homeodomain (LIM-HD) transcription factors act in a combinatorial ‘LIM code’ to control cell fate determination and differentiation. However, our understanding about the role these genes play during regeneration and homeostasis is limited. Here, we report the full repertoire of LIM-HD genes in Schmidtea mediterranea. We found that lim homeobox genes (lhx) appear expressed in complementary patterns along the cephalic ganglia and digestive system of the planarian, with some of them being co-expressed in the same cell types. We have identified that Smed-islet1, -lhx1/5-1, -lhx2/9-3, -lhx6/8, -lmx1a/b-2 and -lmx1a/b-3 are essential to pattern and size the planarian brain as well as for correct regeneration of specific subpopulations of dopaminergic, serotonergic, GABAergic and cholinergic neurons, while Smed-lhx1/5.2 and -lhx2/9.2 are required for the proper expression of intestinal cell type markers, specifically the goblet subtype. LIM-HD are also involved in controlling axonal pathfinding (lhx6/8), axial patterning (islet1, lhx1/5-1, lmx1a/b-3), head/body proportions (islet2) and stem cell proliferation (lhx3/4, lhx2/9-3, lmx1a/b-2, lmx1a/b-3). Altogether, our results suggest that planarians might present a combinatorial LIM code that controls axial patterning, axonal growing and specify distinct neuronal and intestinal cell identities
Co-factors of LIM-HD transcription factors in neural development and axon pathfinding in zebrafish
Full text linkThe zebrafish neuromuscular system is an elegant model to study neural
development.
To reveal a specific programme for zebrafish motor axon pathfinding I
established a method to selectively block motor axon pathfinding by interfering with
LIM domain transcription factor signaling. LIM homeodomain proteins (LIM-HDs)
are an important class of transcriptional regulators and involved in neural
development as well as neuron fate decision in vertebrates. DD domain dimerization
of CLIM (cofactor of LIM-HDs) can activate LIM-HDs and downstream gene
transcription while over-expression of dominant-negative CLIM (DN-CLIM), which
lacks the DD domain, blocks LIM-HD activity. Motor neurons fluoresce in HB9:GFP
transgenic zebrafish as the promoter of the motor neuron specific gene Hb9 drives
expression of GFP. Motor axons in DN-CLIM injected HB9:GFP zebrafish are unable
to exit the spinal cord, instead they grow inside the spinal cord. Thus axon pathfinding,
but not general growth appears to be impaired in these neurons. This provides an
excellent research model to find genes involved in motor axon pathfinding
downstream of LIM-HDs. Gene array expression profiling was carried out on GFP+
motor neurons by fluorescence-activated flow sorting (FACS) with and without prior
injection of DN-CLIM mRNA to elucidate the potential genes relevant to motor axon
pathfinding. Genes that were most strongly down-regulated in DN-CLIM injected
embryos were considered to belong to a motor axon specific guidance programme.
Calca, tac-1 and chodl genes, retrieved from the gene array data, showed specific
expression pattern in motor neuron and obvious down-regulation after DN-CLIM
injection by in situ hybridization. This validated the array results. Chodl contains a
C-type lectin domain representing a potential cell surface receptor for guidance
factors. Gene knock-down experiments with two independent morpholinos led to
stalling of CaP motor axons at the horizontal myoseptum, a pivotal choice point for
axon pathfinding. This suggests that this novel gene specifically affects motor axon
pathfinding in zebrafish.
Single stranded DNA binding protein 1 (SSDP1) functions as an activator of
SSDP1/CLIM/LIM-HD complex which involved in the transcriptional control of
embryonic development. To verify how SSDP1 function in neural development in
zebrafish, I have cloned Zebrafish SSDP1a and SSDP1b, which are most closely
related to mouse and human SSDP1. SSDP1a is widely expressed during zebrafish
development while SSDP1b is specifically expressed in sensory trigeminal and
Rohon-Beard neurons. Over-expression of the N-terminal portion of SSDP1
(N-SSDP1) increases endogenous CLIM protein levels in vivo and impairs the
formation of eyes and midbrain-hindbrain boundary. In addition, SSDP1b knock
down impairs trigeminal and Rohon-Beard sensory axon growth. N-SSDP1 can
partially rescue the inhibition of axon growth induced by DN-CLIM. These results
reveal specific functions of SSDP1 in neural patterning and sensory axon growth
which are in part due to the stabilization of LIM-HD/CLIM complexes.
In summary, co-factors of LIM-HDs play important roles in neural development,
cell fate specification as well as axon pathfinding
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