Macklis Lab

Axons share the decision-making load

February 19, 2019

In neurons, the axon emerges as an independent decision-maker in its own right.

Unlike the familiar blob-like shape of most cells, neurons have distinct regions. The cell body, home to the nucleus, has long been considered the control center of the neuron. The axons and dendrites are seen as the signal-carrying and signal-receiving parts of the neuron. Axons send out long, spindly arms to form connections, called synapses, with other neurons.

Now, research led by investigators at HSCRB suggests that these distinct parts of the neuron are far more complex than once...

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Jeff Macklis, PhD.

A New Way of Looking at Neurons: Jeffrey Macklis receives NIH Pioneer Award funding to study complexity of the subcellular systems within individual neurons

October 5, 2017


As a neuron develops, the axon grows from the central cell body like an arm with many fingers reaching out to explore the surroundings. These fingers, known as growth cones, travel long distances seeking out specific other neurons to form synapses, connective links that create the circuitry in the brain controlling sensation, movement, thinking, and behavior.

The axon and its extensions have typically been thought of like simple cables carrying information between cell bodies, with the cell bodies directing all growth and movement. In fact, axons have...

Read more about A New Way of Looking at Neurons: Jeffrey Macklis receives NIH Pioneer Award funding to study complexity of the subcellular systems within individual neurons
Chen, Z., et al., 2017. Proposed association between the hexanucleotide repeat of C9orf72 and opposability index of the thumb. Amyotroph Lateral Scler Frontotemporal Degener , 18 (3-4) , pp. 175-181.Abstract
OBJECTIVE: Amyotrophic lateral sclerosis (ALS) is a fatal disease caused by motor neuron and sub-cerebral projection neuron degeneration. We sought to explore the particular susceptibility of humans to neurodegeneration and whether any characteristic human features might predispose to selective vulnerability of the critical motor circuitry in ALS. The pathophysiology of the C9orf72 repeat is not yet understood, despite its role as a common cause of ALS and frontotemporal dementia. METHODS: We examined the development of the monosynaptic cortico-motoneuronal system, key to skilled hand movements, measured by the thumb opposability index, and its relationship to the C9orf72 hexanucleotide repeat expansion, a strong predisposing factor for neurodegeneration, using the genomic tool BLAST. RESULTS: We found a statistically significant linear relationship between the C9orf72 hexanucleotide bit score, a measure of genomic conservation of the aligned region across different species, and the thumb opposability index (Pearson's correlation coefficient of 0.78, p value 0.023). The C9orf72 hexanucleotide repeat was only found in humans, chimpanzees and gorillas, species with higher opposability indices. CONCLUSIONS: This may support a role of the hexanucleotide repeat in the same developmental pathways in species with higher prehensility, which may be associated with the selective vulnerability of cortico-motoneuronal cells in humans, manifested most obviously as the 'split hand' syndrome in ALS.
Rodriguez-Muela, N., et al., 2017. Single-Cell Analysis of SMN Reveals Its Broader Role in Neuromuscular Disease. Cell Rep , 18 (6) , pp. 1484-1498. PubMedAbstract
The mechanism underlying selective motor neuron (MN) death remains an essential question in the MN disease field. The MN disease spinal muscular atrophy (SMA) is attributable to reduced levels of the ubiquitous protein SMN. Here, we report that SMN levels are widely variable in MNs within a single genetic background and that this heterogeneity is seen not only in SMA MNs but also in MNs derived from controls and amyotrophic lateral sclerosis (ALS) patients. Furthermore, cells with low SMN are more susceptible to cell death. These findings raise the important clinical implication that some SMN-elevating therapeutics might be effective in MN diseases besides SMA. Supporting this, we found that increasing SMN across all MN populations using an Nedd8-activating enzyme inhibitor promotes survival in both SMA and ALS-derived MNs. Altogether, our work demonstrates that examination of human neurons at the single-cell level can reveal alternative strategies to be explored in the treatment of degenerative diseases.
Itoh, Y., Poulopoulos, A. & Macklis, J.D., 2017. Unfolding the Folding Problem of the Cerebral Cortex: Movin' and Groovin'. Dev Cell , 41 (4) , pp. 332-334. PubMedAbstract
The development of reproducible folding in the gyrencephalic cerebral cortex is a topic of great interest to neuroscientists. In a recent paper in Cell, del Toro et al. (2017) show that changing the adhesive properties of neurons in the normally lissencephalic mouse cortex leads to the formation of stereotyped folding.
Muralidharan, B., et al., 2016. Lhx2 interacts with the NuRD complex and regulates cortical neuron subtype determinants Fezf2 and Sox11. J Neurosci. PubMedAbstract

In the developing cerebral cortex, sequential transcriptional programs take neuroepithelial cells from proliferating progenitors to differentiated neurons with unique molecular identities. The regulatory changes that occur in the chromatin of the progenitors are not well understood. During deep layer neurogenesis, we show that transcription factor Lhx2 binds to distal regulatory elements of Fezf2 and Sox11, critical determinants of neuron subtype identity in the mouse neocortex. We demonstrate that Lhx2 binds to the NuRD histone remodeling complex subunits LSD1, HDAC2, and RBBP4, which are proximal regulators of the epigenetic state of chromatin. When Lhx2 is absent, active histone marks at the Fezf2 and Sox11 loci are increased. Loss of Lhx2 produces an increase, and overexpression of Lhx2 causes a decrease, in layer 5 Fezf2 and Ctip2 expressing neurons. Our results provide mechanistic insight into how Lhx2 acts as a necessary and sufficient regulator of genes that control cortical neuronal subtype identity. SIGNIFICANCE STATEMENT: The functional complexity of the cerebral cortex arises from an array of distinct neuronal subtypes with unique connectivity patterns that are produced from common progenitors. This study reveals that transcription factor Lhx2 regulates the numbers of specific cortical output neuron subtypes by controlling the genes that are required to produce them. Loss or increase in Lhx2 during neurogenesis is sufficient to increase or decrease, respectively, a particular sub-cerebrally projecting population. Mechanistically, Lhx2 interacts with chromatin modifying protein complexes to edit the chromatin landscape of its targets Fezf2 and Sox11, which regulates their expression and consequently the identities of the neurons produced. Thus Lhx2 is a key component of the control network for producing neurons that will participate in cortical circuitry.

Smith, E.C., et al., 2016. Strict in vivo specificity of the Bcl11a erythroid enhancer. Blood. PubMedAbstract

BCL11A, a repressor of human fetal (γ-)globin expression, is required for immune and hematopoietic stem cell functions and brain development. Regulatory sequences within the gene, which are subject to genetic variation affecting fetal globin expression, display hallmarks of an erythroid enhancer in cell lines and transgenic mice. As such this enhancer is a novel, attractive target for therapeutic gene editing. To explore the roles of such sequences in vivo, we generated mice in which the orthologous 10 kb intronic sequences were removed. Bcl11a-enhancer deleted mice (Bcl11a(Δenh)) phenocopy the BCL11A-null state with respect to alterations of globin expression, yet are viable and exhibit no observable blood, brain, or other abnormalities. These preclinical findings provide strong in vivo support for genetic modification of the enhancer for therapy of hemoglobin disorders.

2016 Sep 21

Spinal Cord Injury Awareness Day

12:00pm to 1:00pm


Massachusetts State House, Hall of Flags, Great Hall

The program this year will be an update of research and trials. Our goal to increase funding was achieved on paper with new legislation. Actual numbers will be announced. We need to continue to show our legislators in human terms the value of their commitment. 

The SCI Trust Fund was established in 2004 to provide funding opportunities for SCI research in Massachusetts. To date $750,000 has been allocated to this fund. 

Please join us at the State House to show your support and inform lawmakers about SCI. A buffet lunch will be available.

Fame, R.M., et al., 2016. Cited2 Regulates Neocortical Layer II/III Generation and Somatosensory Callosal Projection Neuron Development and Connectivity. J Neurosci , 36 (24) , pp. 6403-19. PubMedAbstract

The neocortex contains hundreds to thousands of distinct subtypes of precisely connected neurons, allowing it to perform remarkably complex tasks of high-level cognition. Callosal projection neurons (CPN) connect the cerebral hemispheres via the corpus callosum, integrating cortical information and playing key roles in associative cognition. CPN are a strikingly diverse set of neuronal subpopulations, and development of this diversity requires precise control by a complex, interactive set of molecular effectors. We have found that the transcriptional coregulator Cited2 regulates and refines two stages of CPN development. Cited2 is expressed broadly by progenitors in the embryonic day 15.5 subventricular zone, during the peak of superficial layer CPN birth, with a progressive postmitotic refinement in expression, becoming restricted to CPN of the somatosensory cortex postnatally. We generated progenitor-stage and postmitotic forebrain-specific Cited2 conditional knock-out mice, using the Emx1-Cre and NEX-Cre mouse lines, respectively. We demonstrate that Cited2 functions in progenitors, but is not necessary postmitotically, to regulate both (1) broad generation of layer II/III CPN and (2) acquisition of precise area-specific molecular identity and axonal/dendritic connectivity of somatosensory CPN. This novel CPN subtype-specific and area-specific control from progenitor action of Cited2 adds yet another layer of complexity to the multistage developmental regulation of neocortical development. SIGNIFICANCE STATEMENT: This study identifies Cited2 as a novel subtype-specific and area-specific control over development of distinct subpopulations within the broad population of callosal projection neurons (CPN), whose axons connect the two cerebral hemispheres via the corpus callosum (CC). Currently, how the remarkable diversity of CPN subtypes is specified, and how they differentiate to form highly precise and specific circuits, are largely unknown. We found that Cited2 functions within subventricular zone progenitors to both broadly regulate generation of superficial layer CPN throughout the neocortex, and to refine precise area-specific development and connectivity of somatosensory CPN. Gaining insight into molecular development and heterogeneity of CPN will advance understanding of both diverse functions of CPN and of the remarkable range of neurodevelopmental deficits correlated with CPN/CC development.