RESUMEN
Across all sensory modalities, first-stage sensory neurons are an information bottleneck: they must convey all information available for an animal to perceive and act in its environment. Our understanding of coding properties of primary sensory neurons in the auditory and visual systems has been aided by the use of increasingly complex, naturalistic stimulus sets. By comparison, encoding properties of primary somatosensory afferents are poorly understood. Here, we use the rodent whisker system to examine how tactile information is represented in primary sensory neurons of the trigeminal ganglion (Vg). Vg neurons have long been thought to segregate into functional classes associated with separate streams of information processing. However, this view is based on Vg responses to restricted stimulus sets which potentially underreport the coding capabilities of these neurons. In contrast, the current study records Vg responses to complex three-dimensional (3D) stimulation while quantifying the complete 3D whisker shape and mechanics, thereby beginning to reveal their full representational capabilities. The results show that individual Vg neurons simultaneously represent multiple mechanical features of a stimulus, do not preferentially encode principal components of the stimuli, and represent continuous and tiled variations of all available mechanical information. These results directly contrast with proposed codes in which subpopulations of Vg neurons encode select stimulus features. Instead, individual Vg neurons likely overcome the information bottleneck by encoding large regions of a complex sensory space. This proposed tiled and multidimensional representation at the Vg directly constrains the computations performed by more central neurons of the vibrissotrigeminal pathway.
Asunto(s)
Células Receptoras Sensoriales/fisiología , Percepción del Tacto/fisiología , Vibrisas/citología , Vibrisas/fisiología , Animales , Femenino , Imagenología Tridimensional , Modelos Lineales , Ratas Long-EvansRESUMEN
Higher brain function in mammals primarily relies on complex yet sophisticated neuronal circuits in the neocortex. In early developmental stages, neocortical circuits are coarse. Mostly postnatally, the circuits are reorganized to establish mature precise connectivity, in an activity-dependent manner. These connections underlie adult brain function. The rodent somatosensory cortex (barrel cortex) contains a barrel map in layer 4 (L4) and has been considered an ideal model for the study of postnatal neuronal circuit formation since the first report of barrels in 1970. Recently, two-photon microscopy has been used for analyses of neuronal circuit formation in the mammalian brain during early postnatal development. These studies have further highlighted the mouse barrel cortex as an ideal model. In particular, the unique dendritic projection pattern of barrel cortex L4 spiny stellate neurons (barrel neurons) is key for the precise one-to-one functional relationship between whiskers and barrels and thus an important target of studies. In this article, I will review the morphological aspects of postnatal development of neocortical circuits revealed by recent two-photon in vivo imaging studies of the mouse barrel cortex and other related works. The focus of this review will be on barrel neuron dendritic refinement during neonatal development.
Asunto(s)
Dendritas/metabolismo , Neuritas/metabolismo , Corteza Somatosensorial , Vibrisas , Animales , Ratones , Microscopía de Fluorescencia por Excitación Multifotónica , Red Nerviosa/citología , Red Nerviosa/crecimiento & desarrollo , Corteza Somatosensorial/citología , Corteza Somatosensorial/crecimiento & desarrollo , Vibrisas/citología , Vibrisas/inervación , Vibrisas/metabolismoRESUMEN
To interpret the environment, our brain must evaluate external stimuli against internal representations from past experiences. How primary (S1) and secondary (S2) somatosensory cortices process stimuli depending on recent experiences is unclear. Using simultaneous multi-area population imaging of projection neurons and focal optogenetic inactivation, we studied mice performing a whisker-based working memory task. We find that activity reflecting a current stimulus, the recollection of a previous stimulus (cued recall), and the stimulus category are distributed across S1 and S2. Despite this overlapping representation, S2 is important for processing cued recall responses and transmitting these responses to S1. S2 network properties differ from S1, wherein S2 persistently encodes cued recall and the stimulus category under passive conditions. Although both areas encode the stimulus category, only information in S1 is important for task performance through pathways that do not necessarily include S2. These findings reveal both distributed and segregated roles for S1 and S2 in context-dependent sensory processing.
Asunto(s)
Memoria a Corto Plazo , Corteza Somatosensorial/fisiología , Percepción del Tacto , Animales , Masculino , Ratones , Modelos Neurológicos , Neuronas/fisiología , Corteza Somatosensorial/citología , Vibrisas/citología , Vibrisas/fisiologíaRESUMEN
This paper reports on an analytical study of the intrinsic shapes of 523 whiskers from 15 rats. We show that the variety of whiskers on a rat's cheek, each of which has different lengths and shapes, can be described by a simple mathematical equation such that each whisker is represented as an interval on the Euler spiral. When all the representative curves of mystacial vibrissae for a single rat are assembled together, they span an interval extending from one coiled domain of the Euler spiral to the other. We additionally find that each whisker makes nearly the same angle of 47∘ with the normal to the spherical virtual surface formed by the tips of whiskers, which constitutes the rat's tactile sensory shroud or "search space." The implications of the linear curvature model for gaining insight into relationships between growth, form, and function are discussed.
Asunto(s)
Modelos Biológicos , Vibrisas/citología , Vibrisas/fisiología , Algoritmos , Animales , Ratas , TactoRESUMEN
The dermal papilla (DP) is a key mesenchymal compartment of hair follicles that orchestrates mesenchymal-epithelial interaction regulating hair growth cycles. In the present study, we demonstrate that a TALE-family transcription factor, Meis1, is selectively localized in the nucleus of the DP in the anagen phase of the hair cycle. By using an ex vivo organ culture of vibrissae follicles, conditional Meis1 loss causes retardation in hair growth, accompanied by defects in cell proliferation of hair matrix cells. This cell proliferation defect is partly rescued by the addition of culture supernatants derived from Meis1-sufficient but not -deficient DP cells. These findings indicate that nuclear Meis1 in DP activate genes involved in secretion of some unknown factors, which promote proliferation of hair matrix cells in the anagen phase of the hair cycle.
Asunto(s)
Proliferación Celular , Dermis/metabolismo , Folículo Piloso/metabolismo , Cabello/metabolismo , Proteína 1 del Sitio de Integración Viral Ecotrópica Mieloide/metabolismo , Animales , Núcleo Celular/metabolismo , Células Cultivadas , Dermis/citología , Regulación de la Expresión Génica , Cabello/citología , Cabello/crecimiento & desarrollo , Folículo Piloso/citología , Ratones Endogámicos C57BL , Ratones Noqueados , Ratones Transgénicos , Proteína 1 del Sitio de Integración Viral Ecotrópica Mieloide/genética , Técnicas de Cultivo de Órganos , Vibrisas/citología , Vibrisas/metabolismoRESUMEN
The posterior parietal cortex (PPC) in rodents is reciprocally connected to primary somatosensory and vibrissal motor cortices. The PPC neuronal circuitry could thus encode and potentially integrate incoming somatosensory information and whisker motor output. However, the information encoded across PPC layers during refined sensorimotor behavior remains largely unknown. To uncover the sensorimotor features represented in PPC during voluntary whisking and object touch, we performed loose-patch single-unit recordings and extracellular recordings of ensemble activity, covering all layers of PPC in anesthetized and awake, behaving male rats. First, using single-cell receptive field mapping, we revealed the presence of coarse somatotopy along the mediolateral axis in PPC. Second, we found that spiking activity was modulated during exploratory whisking in layers 2-4 and layer 6, but not in layer 5 of awake, behaving rats. Population spiking activity preceded actual movement, and whisker trajectory endpoints could be decoded by population spiking, suggesting that PPC is involved in movement planning. Finally, population spiking activity further increased in response to active whisker touch but only in PPC layers 2-4. Thus, we find layer-specific processing, which emphasizes the computational role of PPC during whisker sensorimotor behavior.SIGNIFICANCE STATEMENT The posterior parietal cortex (PPC) is thought to merge information on motor output and sensory input to orchestrate interaction with the environment, but the function of different PPC microcircuit components is poorly understood. We recorded neuronal activity in rat PPC during sensorimotor behavior involving motor and sensory pathways. We uncovered that PPC layers have dedicated function: motor and sensory information is merged in layers 2-4; layer 6 predominantly represents motor information. Collectively, PPC activity predicts future motor output, thus entailing a motor plan. Our results are important for understanding how PPC computationally processes motor output and sensory input. This understanding may facilitate decoding of brain activity when using brain-machine interfaces to overcome loss of function after, for instance, spinal cord injury.
Asunto(s)
Movimiento/fisiología , Lóbulo Parietal/fisiología , Corteza Somatosensorial/fisiología , Percepción del Tacto/fisiología , Vibrisas/fisiología , Animales , Masculino , Lóbulo Parietal/citología , Ratas , Ratas Wistar , Corteza Somatosensorial/citología , Vibrisas/citología , Vibrisas/inervaciónRESUMEN
Activins and their receptors play important roles in the control of hair follicle morphogenesis, but their role in vibrissae follicle growth remains unclear. To investigate the effect of Activin B on vibrissae follicles, the anagen induction assay and an in vitro vibrissae culture system were constructed. Hematoxylin and eosin staining were performed to determine the hair cycle stages. The 5-ethynyl-2'-deoxyuridine (EdU) and Cell Counting Kit-8 (CCK-8) assays were used to examine the cell proliferation. Flow cytometry was used to detect the cell cycle phase. Inhibitors and Western blot analysis were used to investigate the signaling pathway induced by Activin B. As a result, we found that the vibrissae follicle growth was accelerated by 10 ng/mL Activin B in the anagen induction assay and in an organ culture model. 10 ng/mL Activin B promoted hair matrix cell proliferation in vivo and in vitro. Moreover, Activin B modulates hair matrix cell growth through the ERKâ»Elk1 signaling pathway, and Activin B accelerates hair matrix cell transition from the G1/G0 phase to the S phase through the ERKâ»Cyclin D1 signaling pathway. Taken together, these results demonstrated that Activin B may promote mouse vibrissae growth by stimulating hair matrix cell proliferation and cell cycle progression through ERK signaling.
Asunto(s)
Activinas/farmacología , Ciclo Celular , Folículo Piloso/citología , Sistema de Señalización de MAP Quinasas , Vibrisas/citología , Animales , Ciclo Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Ciclina D1/metabolismo , Folículo Piloso/efectos de los fármacos , Folículo Piloso/crecimiento & desarrollo , Humanos , Sistema de Señalización de MAP Quinasas/efectos de los fármacos , Masculino , Ratones Endogámicos C57BL , Modelos Biológicos , Técnicas de Cultivo de Órganos , Fosforilación/efectos de los fármacos , Proteína Elk-1 con Dominio ets/metabolismoRESUMEN
Loss of one sensory modality can cause other types to become more perceptive (cross-modal plasticity). To test the hypothesis that the loss of vision changes the perceptual threshold in the somatosensory system, we applied optogenetics to directly manipulate the afferent inputs involved in the whisker-barrel system using a transgenic rat (W-TChR2V4) that expresses channelrhodopsin-2 (ChR2) selectively in the large mechanoreceptive neurons in the trigeminal ganglion (TG) and their peripheral nerve terminals. The licking behavior of W-TChR2V4 rat was conditioned to a blue LED light cue on the whisker area while the magnitude and duration of light pulses were varied. The perceptual threshold was thus quantitatively determined for each rat according to the relationship between the magnitude/duration of light and the reaction time between the LED light cue and the first licking event after it. We found that the perceptual threshold was more significantly reduced than the control non-deprived rats when the rats were visually deprived at postnatal 26-30 days (P26-30, early VD group), but not at P58-66 (late VD group). However, the sensory threshold of a late VD animal was similar to that of a control. Our results suggest the presence of cross-modal plasticity by which the loss of vision at the juvenile period increased the sensitivity of the somatosensory system involved in the touch of whiskers.
Asunto(s)
Plasticidad Neuronal/fisiología , Umbral Sensorial/fisiología , Corteza Somatosensorial/fisiología , Tacto/fisiología , Vibrisas/fisiología , Visión Ocular/fisiología , Animales , Condicionamiento Psicológico , Femenino , Aseo Animal/fisiología , Luz , Masculino , Mecanorreceptores/citología , Mecanorreceptores/fisiología , Optogenética/métodos , Nervios Periféricos/citología , Nervios Periféricos/fisiología , Ratas , Ratas Transgénicas , Corteza Somatosensorial/citología , Factores de Tiempo , Ganglio del Trigémino/citología , Ganglio del Trigémino/fisiología , Vibrisas/citologíaRESUMEN
Hair follicle outer root sheath (ORS) cells can be expanded in vitro, but often lose receptivity to hair-inducing dermal signals. Recent studies have shown hair-inductive activity (trichogenicity) can be restored in rat ORS cells expanded with a fibroblast feeder by co-culturing with rat vibrissae dermal papilla (DP) cells. In this study, we investigated whether the trichogenicity of human ORS cells can be restored by co-culturing with human DP cells. ORS cells from human scalp hair follicles were cultured independently or with DP cells for 5 days and implanted into nude mice alongside freshly isolated neonatal mouse dermal cells. Although there was no hair induction when monocultured ORS cells were implanted, it was observed in co-cultured ORS cells. We also observed differential regulation of a number of genes in ORS cells co-cultured with DP cells compared to monocultured ORS cells as examined by microarray. Taken together, our data strongly suggest that human DP cells restore the trichogenicity of co-cultured ORS cells by influencing ORS gene expression through paracrine factors.
Asunto(s)
Dermis/citología , Queratinocitos/fisiología , Animales , Células Cultivadas , Técnicas de Cocultivo , Perfilación de la Expresión Génica , Folículo Piloso/citología , Folículo Piloso/trasplante , Humanos , Queratinocitos/citología , Ratones , Análisis por Micromatrices , Comunicación Paracrina , Trasplante Heterólogo , Vibrisas/citologíaRESUMEN
To test how cerebellar crus I/II Purkinje cells and their targets in the lateral cerebellar nuclei (CbN) integrate sensory and motor-related inputs and contribute to reflexive movements, we recorded extracellularly in awake, head-fixed mice during non-contact whisking. Ipsilateral or contralateral air puffs elicited changes in population Purkinje simple spike rates that matched whisking kinematics (â¼1 Hz/1° protraction). Responses remained relatively unaffected when ipsilateral sensory feedback was removed by lidocaine but were reduced by optogenetically inhibiting the reticular nuclei. Optogenetically silencing cerebellar output suppressed movements. During puff-evoked whisks, both Purkinje and CbN cells generated well-timed spikes in sequential 2- to 4-ms windows at response onset, such that they alternately elevated their firing rates just before protraction. With spontaneous whisks, which were smaller than puff-evoked whisks, well-timed spikes were absent and CbN cells were inhibited. Thus, sensory input can facilitate millisecond-scale, well-timed spiking in Purkinje and CbN cells and amplify reflexive whisker movements.
Asunto(s)
Potenciales de Acción/fisiología , Corteza Cerebelosa/fisiología , Cerebelo/fisiología , Red Nerviosa/fisiología , Vibrisas/fisiología , Animales , Corteza Cerebelosa/química , Corteza Cerebelosa/citología , Cerebelo/química , Cerebelo/citología , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Red Nerviosa/química , Red Nerviosa/citología , Células de Purkinje/química , Células de Purkinje/fisiología , Vibrisas/citología , Vibrisas/inervaciónRESUMEN
OBJECTIVES: To explore potential effects of recombinant human fibroblast growth factor 20 (rhFGF20) in the growth of cultured mouse vibrissal follicles. RESULTS: The growth of cultured mouse vibrissal follicles was significantly induced by rhFGF20 in a dose dependent pattern in the in vitro vibrissal follicle organ culture model. However, too high concentration of rhFGF20 could inhibit the growth of vibrissal follicles. We further demonstrated that rhFGF20 stimulated the proliferation of hair matrix cells and activated Wnt/ß-catenin signaling pathway. CONCLUSIONS: The rhFGF20 might be a potential therapeutic agent to treat hair loss disorders.
Asunto(s)
Factores de Crecimiento de Fibroblastos/farmacología , Folículo Piloso/efectos de los fármacos , Proteínas Recombinantes/farmacología , Vibrisas/efectos de los fármacos , Animales , Proliferación Celular/efectos de los fármacos , Femenino , Folículo Piloso/citología , Folículo Piloso/metabolismo , Humanos , Ratones , Ratones Endogámicos C57BL , Técnicas de Cultivo de Tejidos , Regulación hacia Arriba/efectos de los fármacos , Vibrisas/citología , Vibrisas/metabolismo , Vía de Señalización Wnt/efectos de los fármacosAsunto(s)
Folículo Piloso/metabolismo , Complejo Represivo Polycomb 1/genética , Telomerasa/metabolismo , Vibrisas/metabolismo , Animales , Células Cultivadas , Folículo Piloso/citología , Folículo Piloso/crecimiento & desarrollo , Humanos , Ratones , Fenotipo , Complejo Represivo Polycomb 1/metabolismo , Transducción de Señal , Telomerasa/genética , Factores de Tiempo , Transfección , Regulación hacia Arriba , Vibrisas/citologíaAsunto(s)
Tinturas para el Cabello/efectos adversos , Folículo Piloso/efectos de los fármacos , Peróxido de Hidrógeno/efectos adversos , Transducción de Señal/efectos de los fármacos , beta Catenina/metabolismo , Animales , Línea Celular , Ciclina D1/metabolismo , Regulación hacia Abajo/efectos de los fármacos , Glucógeno Sintasa Quinasa 3 beta/metabolismo , Tinturas para el Cabello/química , Folículo Piloso/citología , Folículo Piloso/crecimiento & desarrollo , Voluntarios Sanos , Humanos , Litio/administración & dosificación , Masculino , Estrés Oxidativo/efectos de los fármacos , Cultivo Primario de Células , Ratas , Cuero Cabelludo , Vibrisas/citologíaRESUMEN
The rodent somatosensory cortex includes well-defined examples of cortical columns-the barrel columns-that extend throughout the cortical depth and are defined by discrete clusters of neurons in layer 4 (L4) called barrels. Using the cell-type-specific Ntsr1-Cre mouse line, we found that L6 contains infrabarrels, readily identifiable units that align with the L4 barrels. Corticothalamic (CT) neurons and their local axons cluster within the infrabarrels, whereas corticocortical (CC) neurons are densest between infrabarrels. Optogenetic experiments showed that CC cells received robust input from somatosensory thalamic nuclei, whereas CT cells received much weaker thalamic inputs. We also found that CT neurons are intrinsically less excitable, revealing that both synaptic and intrinsic mechanisms contribute to the low firing rates of CT neurons often reported in vivo. In summary, infrabarrels are discrete cortical circuit modules containing two partially separated excitatory networks that link long-distance thalamic inputs with specific outputs.
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Vías Nerviosas/fisiología , Neuronas/fisiología , Corteza Somatosensorial/fisiología , Tálamo/fisiología , Vibrisas/fisiología , Animales , Recuento de Células , Ratones , Ratones Transgénicos , Vías Nerviosas/ultraestructura , Neuronas/clasificación , Neuronas/ultraestructura , Corteza Somatosensorial/ultraestructura , Tálamo/ultraestructura , Vibrisas/citologíaRESUMEN
Histological data from terrestrial, semiaquatic, and fully aquatic mammal vibrissa (whisker) studies indicate that follicle microstructure and innervation vary across the mystacial vibrissal array (i.e. medial microvibrissae to lateral macrovibrissae). However, comparative data are lacking, and current histological studies on pinniped vibrissae only focus on the largest ventrolateral vibrissae. Consequently, we investigated the microstructure, medial-to-lateral innervation, and morphometric trends in harp seal (Pagophilus groenlandicus) vibrissal follicle-sinus complexes (F-SCs). The F-SCs were sectioned either longitudinally or in cross-section and stained with a modified Masson's trichrome stain (microstructure) or Bodian's silver stain (innervation). All F-SCs exhibited a tripartite blood organization system. The dermal capsule thickness, the distribution of major branches of the deep vibrissal nerve, and the hair shaft design were more symmetrical in medial F-SCs, but these features became more asymmetrical as the F-SCs became more lateral. Overall, the mean axon count was 1,221 ± 422.3 axons/F-SC and mean axon counts by column ranged from 550 ± 97.4 axons/F-SC (medially, column 11) to 1,632 ± 173.2 axons/F-SC (laterally, column 2). These values indicate a total of 117,216 axons innervating the entire mystacial vibrissal array. The mean axon count of lateral F-SCs was 1,533 ± 192.9 axons/ F-SC, which is similar to values reported in the literature for other pinniped F-SCs. Our data suggest that conventional studies that only examine the largest ventrolateral vibrissae may overestimate the total innervation by â¼20%. However, our study also accounts for variation in quantification methods and shows that conventional analyses likely only overestimate innervation by â¼10%. The relationship between axon count and cross-sectional F-SC surface area was nonlinear, and axon densities were consistent across the snout. Our data indicate that harp seals exhibit microstructural and innervational differences between their microvibrissae (columns 8-11) and macrovibrissae (columns 1-7). We hypothesize that this feature is conserved among pinnipeds and may result in functional compartmentalization within their mystacial vibrissal arrays.
Asunto(s)
Axones , Phocidae/fisiología , Vibrisas/citología , Vibrisas/inervación , Animales , Recuento de CélulasRESUMEN
Isolated whisker follicles from nestin-driven green fluorescent protein (ND-GFP) mice, containing hair-associated pluripotent (HAP) stem cells, were histocultured in three dimensions on Gelfoam(®) for 3 weeks for subsequent transplantation to the spinal cord in order to heal an induced injury with the HAP stem cells. The hair shafts were removed from Gelfoam(®)-histocultured whisker follicles, and the remaining parts of the whisker follicles, containing GFP-nestin-expressing (HAP) stem cells, were transplanted into the injured spinal cord of nude mice, along with the Gelfoam(®). After 90 days, the mice were sacrificed and the spinal cord injuries were observed to have healed. ND-GFP expression was intense at the healed area of the spinal cord, as observed by fluorescence microscopy, demonstrating that the HAP stem cells were involved in healing the spinal cord. The transplanted whisker follicles produced remarkably long hair shafts in the spinal cord over 90 days and curved and enclosed the spinal cord. This result changes our concept of hair growth, demonstrating it is not limited to the skin and that hair growth appears related to HAP stem cells as both increased in tandem on the spinal cord.
Asunto(s)
Folículo Piloso/citología , Folículo Piloso/trasplante , Células Madre Pluripotentes/citología , Células Madre Pluripotentes/metabolismo , Regeneración de la Medula Espinal , Vibrisas/citología , Animales , Modelos Animales de Enfermedad , Expresión Génica , Genes Reporteros , Proteínas Fluorescentes Verdes/genética , Ratones , Ratones Transgénicos , Nestina/genética , Traumatismos de la Médula Espinal/terapiaRESUMEN
We have previously discovered nestin-expressing hair-follicle-associated pluripotent (HAP) stem cells and have shown that they can differentiate to neurons, glia, and many other cell types. HAP stem cells can be used for nerve and spinal cord repair. We have recently shown the HAP stem cells can differentiate to beating heart-muscle cells and tissue sheets of beating heart-muscle cells. In the present study, we determined the efficiency of HAP stem cells from mouse vibrissa hair follicles of various ages to differentiate to beating heart-muscle cells. We observed that the whiskers located near the ear were more efficient to differentiate to cardiac-muscle cells compared to whiskers located near the nose. Differentiation to cardiac-muscle cells from HAP stem cells in cultured whiskers in 4-week-old mice was significantly greater than in 10-, 20-, and 40-week-old mice. There was a strong decrease in differentiation potential of HAP stem cells to cardiac-muscle cells by 10 weeks of age. In contrast, the differentiation potential of HAP stem cells to other cell types did not decrease with age. The possibility of rejuvenation of HAP stem cells to differentiate at high efficiency to cardiac-muscle cells is discussed.
Asunto(s)
Envejecimiento/fisiología , Diferenciación Celular , Folículo Piloso/citología , Miocitos Cardíacos/citología , Células Madre Pluripotentes/citología , Animales , Biomarcadores/metabolismo , Ratones Endogámicos C57BL , Miocitos Cardíacos/metabolismo , Células Madre Pluripotentes/metabolismo , ARN Mensajero/genética , ARN Mensajero/metabolismo , Vibrisas/citologíaRESUMEN
Coordinating cell differentiation with cell growth and division is crucial for the successful development, homeostasis and regeneration of multicellular tissues. Here, we use bristle patterning in the fly notum as a model system to explore the regulatory and functional coupling of cell cycle progression and cell fate decision-making. The pattern of bristles and intervening epithelial cells (ECs) becomes established through Notch-mediated lateral inhibition during G2 phase of the cell cycle, as neighbouring cells physically interact with each other via lateral contacts and/or basal protrusions. Since Notch signalling controls cell division timing downstream of Cdc25, ECs in lateral contact with a Delta-expressing cell experience higher levels of Notch signalling and divide first, followed by more distant neighbours, and lastly Delta-expressing cells. Conversely, mitotic entry and cell division makes ECs refractory to lateral inhibition signalling, fixing their fate. Using a combination of experiments and computational modelling, we show that this reciprocal relationship between Notch signalling and cell cycle progression acts like a developmental clock, providing a delimited window of time during which cells decide their fate, ensuring efficient and orderly bristle patterning.
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Tipificación del Cuerpo , Ciclo Celular , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/embriología , Drosophila melanogaster/metabolismo , Péptidos y Proteínas de Señalización Intracelular/metabolismo , Proteínas de la Membrana/metabolismo , Receptores Notch/metabolismo , Transducción de Señal , Animales , Drosophila melanogaster/citología , Células Epiteliales/citología , Células Epiteliales/metabolismo , Órganos de los Sentidos/citología , Células Madre/citología , Células Madre/metabolismo , Factores de Tiempo , Vibrisas/citología , Vibrisas/embriologíaRESUMEN
Hair follicle cells contribute to wound healing, skin circulation, and skin diseases including skin cancer, and hair transplantation is a useful technique to study the participation of hair follicle cells in skin homeostasis and wound healing. Although hair follicle transplantation is a well-established human hair-restoration procedure, follicular transplantation techniques in animals have a number of shortcomings and have not been well described or optimized. To facilitate the study of follicular stem and progenitor cells and their interaction with surrounding skin, we have established a new murine transplantation model, similar to follicular unit transplantation in humans. Vibrissae from GFP transgenic mice were harvested, flip-side microdissected, and implanted individually into needle hole incisions in the back skin of immune-deficient nude mice. Grafts were evaluated histologically and the growth of transplanted vibrissae was observed. Transplanted follicles cycled spontaneously and newly formed hair shafts emerged from the skin after 2 weeks. Ninety percent of grafted vibrissae produced a hair shaft at 6 weeks. After pluck-induced follicle cycling, growth rates were equivalent to ungrafted vibrissae. Transplanted vibrissae with GFP-positive cells were easily identified in histological sections. We established a follicular vibrissa transplantation method that recapitulates human follicular unit transplantation. This method has several advantages over current protocols for animal hair transplantation. The method requires no suturing and minimizes the damage to donor follicles and recipient skin. Vibrissae are easier to microdissect and transplant than pelage follicles and, once transplanted, are readily distinguished from host pelage hair. This facilitates measurement of hair growth. Flip-side hair follicle microdissection precisely separates donor follicular tissue from interfollicular tissue and donor cells remain confined to hair follicles. This makes it possible to differentiate migration of hair follicle cells from interfollicular epidermis in lineage tracing wound experiments using genetically labeled donor follicles.
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Folículo Piloso/trasplante , Trasplante de Piel/métodos , Vibrisas/trasplante , Cicatrización de Heridas/fisiología , Animales , Diferenciación Celular , Movimiento Celular , Folículo Piloso/citología , Folículo Piloso/crecimiento & desarrollo , Masculino , Ratones , Ratones Desnudos , Ratones Transgénicos , Microdisección/métodos , Modelos Animales , Fenómenos Fisiológicos de la Piel , Células Madre/fisiología , Vibrisas/citología , Vibrisas/crecimiento & desarrolloRESUMEN
Mouse whiskers are somatotopically mapped in brainstem trigeminal nuclei as neuronal modules known as barrelettes. Whisker-related afferents form barrelettes in ventral principal sensory (vPrV) nucleus, whereas mandibular input targets dorsal PrV (dPrV). How barrelette neuron identity and circuitry is established is poorly understood. We found that ectopic Hoxa2 expression in dPrV neurons is sufficient to attract whisker-related afferents, induce asymmetrical dendrite arbors, and allow ectopic barrelette map formation. Moreover, the thalamic area forming whisker-related barreloids is prenatally targeted by both vPrV and dPrV axons followed by perinatal large-scale pruning of dPrV axons and refinement of vPrV barrelette input. Ectopic Hoxa2 expression allows topographically directed targeting and refinement of dPrV axons with vPrV axons into a single whisker-related barreloid map. Thus, a single HOX transcription factor is sufficient to switch dPrV into a vPrV barrelette neuron program and coordinate input-output topographic connectivity of a dermatome-specific circuit module.