Biology subjects

Scott, K.

Publications and source records attributed to Scott, K..

25 records · Page 2Linked to original sources

bioRxiv2021

Fmrp regulates oligodendrocyte lineage cell specification and differentiation

Neurodevelopment requires the precise integration of a wide variety of neuronal and glial cell types. During early embryonic development, motor neurons and then oligodendrocyte precursor cells (OPCs) are specified from neural progenitors residing in the periventricular pMN progenitor domain of the spinal cord. Following gliogenesis, OPCs can differentiate as oligodendrocytes (OLs) - the myelinating glial cells of the central nervous system - or remain as OPCs. To generate unique cell types capable of highly divergent functions, these specification and differentiation events require specialized gene expression programs. RNA binding proteins (RBPs) regulate mRNA localization and translation in the developing nervous system and are linked to many neurodevelopmental disorders. One example is Fragile X syndrome (FXS), caused by the loss of the RBP fragile X mental retardation protein (FMRP). Importantly, infants with FXS have reduced white matter and we previously showed that zebrafish Fmrp is autonomously required in OLs to promote myelin sheath growth. We now find that Fmrp regulates cell specification in pMN progenitor cells and subsequently promotes differentiation of OPCs, such that fmr1 mutant zebrafish embryos generate excess OPCs and fewer differentiating OLs in the developing spinal cord. Although the early patterning of spinal progenitor domains appears largely normal in fmr1 mutants during early embryogenesis, Shh signaling is greatly diminished. Taken together, these results suggest cell stage-specific requirements for Fmrp in the specification and differentiation of oligodendrocyte lineage cells.

developmental biology↗

bioRxiv2021

Zebrafish spinal cord oligodendrocyte formation requires boc function

The axis of the vertebrate neural tube is patterned, in part, by a ventral to dorsal gradient of Shh signaling. In the ventral spinal cord, Shh induces concentration-dependent expression of transcription factors, subdividing neural progenitors into distinct domains that subsequently produce distinct neuronal and glial subtypes. In particular, progenitors of the pMN domain express the bHLH transcription factor Olig2 and produce motor neurons followed by oligodendrocytes, the myelinating glial cell type of the central nervous system. In addition to its role in patterning ventral progenitors, Shh signaling must be maintained through development to specify pMN progenitors for oligodendrocyte fate. Using a forward genetic screen in zebrafish for mutations that disrupt development of oligodendrocytes, we identified a new mutant allele of boc, which encodes a type I transmembrane protein that functions as a coreceptor for Shh. Embryos homozygous for the bocco25 allele, which creates a missense mutation in a Fibronectin type III domain that binds Shh, have normally patterned spinal cords but fail to maintain pMN progenitors, resulting in a deficit of oligodendrocytes. Using a sensitive fluorescent detection method for in situ RNA hybridization, we found that spinal cord cells express boc in a graded fashion that is inverse to the gradient of Shh signaling activity and that boc function is necessary to maintain pMN progenitors by shaping the Shh signaling gradient.

developmental biology↗

bioRxiv2020

Transfer function for YAP/TAZ nuclear translocation revealed through spatial systems modeling

YAP/TAZ is a master regulator of mechanotransduction whose functions rely on translocation from the cytoplasm to the nucleus in response to diverse physical cues. Substrate stiffness, substrate dimensionality, and cell shape are all input signals for YAP/TAZ, and through this pathway, regulate critical cellular functions and tissue homeostasis. Yet, the relative contributions of each biophysical signal and the mechanisms by which they synergistically regulate YAP/TAZ in realistic tissue microenvironments that provide multiplexed input signals remains unclear. For example, in simple 2D culture, YAP/TAZ nuclear localization correlates strongly with substrate stiffness, while in 3D environments, YAP/TAZ translocation can increase with stiffness, decrease with stiffness, or remain unchanged. Here, we develop a spatial model of YAP/TAZ translocation to enable quantitative analysis of the relationships between substrate stiffness, substrate dimensionality, and cell shape. Our model couples cytosolic stiffness to nuclear mechanics to replicate existing experimental trends, and extends beyond current data to predict that increasing substrate activation area through changes in culture dimensionality, while conserving cell volume, forces distinct shape changes that result in nonlinear effect on YAP/TAZ nuclear localization. Moreover, differences in substrate activation area versus total membrane area can account for counterintuitive trends in YAP/TAZ nuclear localization in 3D culture. Based on this multiscale investigation of the different system features of YAP/TAZ nuclear translocation, we predict that how a cell reads its environment is a complex information transfer function of multiple mechanical and biochemical factors. These predictions reveal design principles of cellular and tissue engineering for YAP/TAZ mechanotransduction. STATEMENT OF SIGNIFICANCEIn chemical engineering, a transfer function is a mathematical function that models the output of a reactor for all possible inputs, and enables the reliable design and operation of complex reaction systems. Here, we apply this principle to cells to derive the transfer function by which substrate stiffness is converted into YAP/TAZ nuclear localization. This function is defined by a spatial model of the YAP/TAZ mechano-chemical sensing network, wherein key spatial and physical inputs to the system, namely cell and nuclear shape, surface area to volume ratios of cytoplasmic and nuclear compartments, substrate dimensionality, substrate activation area, and substrate stiffness, are all integrated. The resulting model accounts for seemingly contradictory experimental trends and lends new insight into controlling YAP/TAZ signalling.

biophysics↗

bioRxiv2020

Central and peripheral GLP-1 systems independently and additively suppress eating

The anorexigenic peptide glucagon-like peptide-1 (GLP-1) is secreted from gut enteroendocrine cells and brain preproglucagon (PPG) neurons, which respectively define the peripheral and central GLP-1 systems. As peripheral satiation signals are integrated in the nucleus tractus solitarius (NTS), PPGNTS neurons are assumed to link the peripheral and central GLP-1 systems, forming a unified GLP-1 gut-brain satiation circuit. This hypothesis, however, remains unsubstantiated. We report that PPGNTS neurons encode satiation in mice, consistent with vagal gastrointestinal distension signalling. However, PPGNTS neurons predominantly receive vagal input from oxytocin receptor-expressing vagal neurons, rather than those expressing GLP-1 receptors. Furthermore, PPGNTS neurons are not necessary for eating suppression induced by the GLP-1 receptor agonists liraglutide or semaglutide, and semaglutide and PPGNTS neuron activation additively suppress eating. Central and peripheral GLP-1 systems thus suppress eating via independent gut-brain circuits, hence PPGNTS neurons represent a rational pharmacological target for anti-obesity combination therapy with GLP-1 receptor agonists. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/234427v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@1c7643aorg.highwire.dtl.DTLVardef@18520daorg.highwire.dtl.DTLVardef@12fc8fdorg.highwire.dtl.DTLVardef@34809b_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract: C_FIG

neuroscience↗

bioRxiv2020

Prdm8 regulates pMN progenitor specification for motor neuron and oligodendrocyte fates by modulating Shh signaling response

Spinal cord pMN progenitors sequentially produce motor neurons and oligodendrocyte precursor cells (OPCs). Some OPCs differentiate rapidly as myelinating oligodendrocytes whereas others remain into adulthood. How pMN progenitors switch from producing motor neurons to OPCs with distinct fates is poorly understood. pMN progenitors express prdm8, which encodes a transcriptional repressor, during motor neuron and OPC formation. To determine if prdm8 controls pMN cell fate specification, we used zebrafish as a model system to investigate prdm8 function. Our analysis revealed that prdm8 mutant embryos have a deficit of motor neurons resulting from a premature switch from motor neuron to OPC production. Additionally, prdm8 mutant larvae have excess oligodendrocytes and a concomitant deficit of OPCs. Notably, pMN cells of mutant embryos have elevated Shh signaling coincident with the motor neuron to OPC switch. Inhibition of Shh signaling restored the number of motor neurons to normal but did not rescue the proportion of oligodendrocytes. These data suggest that Prdm8 regulates the motor neuron-OPC switch by controlling the level of Shh activity in pMN progenitors and also regulates allocation of oligodendrocyte lineage cell fates. Summary StatementPrdm8 regulates the timing of a motor neuron-oligodendrocyte switch and oligodendrocyte lineage cell identity in the zebrafish spinal cord.

developmental biology↗

bioRxiv2019

Two brain pathways initiate distinct forward walking programs in Drosophila

An animal at rest or engaged in stationary behaviors can instantaneously initiate goal-directed walking. How descending brain inputs trigger rapid transitions from a non-walking state to an appropriate walking state is unclear. Here, we identify two specific neuronal classes in the Drosophila brain that drive two distinct forward walking programs in a context-specific manner. The first class, named P9, consists of descending neurons that drive forward walking with ipsilateral turning. P9 receives inputs from central courtship-promoting neurons and visual projection neurons and is necessary for a male to track a female during courtship. The second class comprises novel, higher order neurons, named BPN, that drives straight, forward walking. BPN is required for high velocity walking and is active during long, fast, straight walking bouts. Thus, this study reveals separate brain pathways for object-directed steering and fast straight walking, providing insight into how the brain initiates different walking programs.

neuroscience↗

bioRxiv2019

Activation of specific mushroom body output neurons inhibits proboscis extension and feeding behavior

The ability to modify behavior based on prior experience is essential to an animals survival. For example, animals may become attracted to a previously neutral odor or reject a previously appetitive food source upon learning. In Drosophila, the mushroom bodies (MBs) are critical for olfactory associative learning and conditioned taste aversion, but how the output of the MBs affects specific behavioral responses is unresolved. In conditioned taste aversion, Drosophila shows a specific behavioral change upon learning: proboscis extension to sugar is reduced after a sugar stimulus is paired with an aversive stimulus. While studies have identified MB output neurons (MBONs) that drive approach or avoidance behavior, whether the same MBONs impact proboscis extension behavior is unknown. Here, we tested the role of MB pathways in modulating proboscis extension and identified 10 MBON split-GAL4 lines that upon activation significantly decreased proboscis extension to sugar. Activating several of these lines also decreased sugar consumption, revealing that these MBONs have a general role in modifying feeding behavior beyond proboscis extension. Although the MBONs that decreased proboscis extension and ingestion are different from those that drive avoidance behavior in another context, the diversity of their arborizations demonstrates that a distributed network influences proboscis extension behavior. These studies provide insight into how the MB flexibly alters the response to taste compounds and modifies feeding decisions.

neuroscience↗