This research was conducted to investigate the expression of porcine intestinal nutrient transporters along the neonatal crypt-villus axis and during the postnatal development. First, we examined the transport kinetics of Na+-glucose co-tranporter 1 (SGLT1) and Na+-dependent neutral amino acid (AA) transporter B0AT1 and then the protein and mRNA abundances of SGLT1, B0AT1 and Na+-dependent neutral AA exchanger ASCT2 along the jejunal crypt-villus axis in the neonatal pig and the potential mechanisms associated with their regulations. Our results suggested that: 1) high levels of apical maximal SGLT1 and B0AT1 uptake activities were shown to exist along the entire jejunal crypt-villus axis in the neonatal pig; 2) there were no significant differences in the SGLT1, B0AT1 and ASCT2 protein abundances in spite of their different mRNA abundances among the crypt-villus axis, suggesting unique posttranscriptional regulatory mechanisms; and 3) global protein translational efficiency, as assessed by examining some of the key protein translational initiation and elongation factors, was higher in the crypt cells than in the upper villus cells, likely playing a regulatory role for maintaining apical nutrient transporter abundances in crypt cells of the neonate. Second, we further examined the protein and mRNA abundances of jejunal neutral AA transporters B0AT1 and ASCT2 and acidic AA transporter EAAC1 during the postnatal development in pigs at the ages of d 1, 4, 6, 12, 20, 28 (1-wk post-weaning), and 70 (mature gut at grower phase), respectively. Our results showed that the jejunal apical B0AT1, ASCT2 and EAAC1 protein abundances were dramatically decreased during the postnatal development and were likely regulated at both the transcriptional and post-transcriptional levels. These substantial decreases in the small intestinal apical Na+-dependent AA transporter abundances may contribute to increased intestinal microbial catabolism of AA, which may be partially responsible for the reduced whole body efficiency of nitrogen utilization during the postnatal growth in pigs. Collectively, our results suggest that apical nutrient transporters SGLT1, B0AT1 and ASCT2 are abundantly expressed along the entire jejunal crypt-villus axis in the neonatal pig, whereas abundances of jejunal apical AA transporters EAAC1, B0AT1 and ASCT2 declined substantially during the postnatal growth in pigs.

Malgré sa complexité, le cerveau intègre en permanence de nouvelles cellules – à la fois neuronales et gliales – au-delà du développement embryonnaire et ce, tout le long de la vie. La période postnatale est caractérisée par une gliogenèse intense. A l’âge adulte, de nouveaux neurones et cellules gliales sont produits dans des régions restreintes à partir de cellules souches/progénitrices (CSP) localisées dans des niches. Les deux niches de CSP adultes les mieux décrites sont la zone sous-ventriculaire des ventricules latéraux, qui produit de nouveaux interneurones olfactifs, et la zone sous-granulaire du gyrus denté de l’hippocampe, où de nouveaux neurones en grain sont produits localement. Des travaux menés ces dernières années ont montré qu’une neuro- et une gliogenèse avaient aussi lieu dans l’hypothalamus postnatal, une petite région du diencéphale ventral qui régule des processus physiologiques vitaux tels que le métabolisme, la reproduction, le sommeil et la thermorégulation. Si l’identité des CSP hypothalamiques reste débattue, de nombreux travaux s’accordent sur l’importance de la neurogenèse hypothalamique postnatale dans le contrôle du métabolisme. Cependant, la possibilité que la genèse postnatale de cellules contribue aussi au contrôle de la fonction de reproduction, une autre fonction clé de l’hypothalamus, restait à explorer. L’objectif premier de mon travail de thèse était de rechercher si la genèse de cellules dans l’hypothalamus postnatal est impliquée dans le contrôle de la reproduction, une fonction physiologique qui requière un haut degré de plasticité. La fonction de reproduction est orchestrée par une petite population de neurones produisant la neurohormone Gonadotrophin-Releasing Hormone (GnRH). Ces neurones, qui naissent en dehors du cerveau, sont en place dans la région préoptique (RPO) de l’hypothalamus à la naissance. Cependant, ils doivent subir une maturation postnatale pour acquérir le profil de sécrétion qui leur permettra d’initier la puberté et d’assurer la fertilité de l’individu. Dans une première étude, grâce à une combinaison d’approches in vitro et in vivo, nous avons mis en évidence une vague d’astrogenèse dans l’environnement des neurones à GnRH au sein de la RPO au cours des deux premières semaines de vie postnatale chez la ratte. Nos résultats suggèrent que les neurones à GnRH utilisent la prostaglandine D2 pour attirer les progéniteurs environnants et que ce recrutement est important pour la maturation sexuelle. Dans une deuxième étude, nous avons recherché si de nouvelles cellules naissent à l’âge adulte dans des régions hypothalamiques qui contrôlent la fonction de reproduction. Nous montrons que des cellules sont produites dans la RPO chez la ratte adulte et que leur taux varie au cours du cycle oestral, suggérant une régulation par les stéroïdes sexuels. De plus, nous montrons que la survenue d’une gestation stimule la néogenèse cellulaire dans une zone de la RPO qui contrôle le comportement maternel. Si la néogenèse hypothalamique adulte a surtout été étudiée chez les rongeurs de laboratoire, il reste à déterminer si ce phénomène existe aussi chez l’homme. Pour aborder cette question, nous avons évalué dans une troisième étude l’expression de marqueurs de CSP dans l’hypothalamus humain adulte, comparativement au rongeur (souris, rat) et à un primate lémurien, le microcèbe. Nous montrons que l’hypothalamus humain adulte contient des populations de cellules au profil antigénique de CSP, dont certaines semblent propres à l’homme. Au total, ces travaux montrent que de nouvelles cellules naissent dans des régions hypothalamiques qui contrôlent la fonction de reproduction au cours de la vie postnatale et à l’âge adulte chez la ratte, et que ce phénomène est important pour la maturation sexuelle. L’observation de CSP putatives dans l’hypothalamus humain adulte suggère que la capacité de l’hypothalamus à produire de nouvelles cellules à l’âge adulte existe aussi dans notre espèce. / Despite its complexity, the brain keeps adding new cells – both neuronal and glial – beyond embryonic development and throughout life. The postnatal period is characterized by intense and widespread gliogenesis. During adulthood, both glio- and neurogenesis occur in restricted locations from stem/progenitor cells (NPC) residing in niches. The two best-described niches of adult NPC are the subventricular zone of the lateral ventricles, which provides new interneurons to the olfactory bulb, and the subgranular zone of the hippocampal dentate gyrus that locally produces new granule cells. The last decade has seen an accumulation of studies showing that neuro- and gliogenesis also occur in the postnatal hypothalamus, a small portion of the ventral forebrain surrounding the third ventricle that regulates essential physiological processes such as metabolism, reproduction, sleep and thermoregulation. Even though the identity of hypothalamic NPC remains a matter of debate, a growing body of evidence points to postnatal hypothalamic neurogenesis relevance for the control of metabolism. However, a possible contribution of postnatal hypothalamic cell generation to the central control of reproduction, another key function of the hypothalamus, remained to be explored.The main aim of my doctoral researches was to evaluate whether the generation of new cells in the postnatal hypothalamus contributes to the central control of reproduction, a physiological function known to require a high degree of plasticity. The reproductive function is controlled by a small population of neurons producing the neurohormone Gonadotrophin-Releasing Hormone (GnRH). These neurons, which are born in the nasal placodes, are in place at birth in the preoptic area (POA) of the hypothalamus. However, they need a postnatal maturation to reach a mature secretory pattern that will trigger puberty and subsequent fertility.In a first study, using a combination of in vitro and in vivo experiments, we showed that a wave of astrogenesis occurs in the POA from local progenitors in the environment of GnRH neurons during the first weeks of postnatal life in the female rat. We identified prostaglandin D2 as a factor used by GnRH neurons to attract progenitors in their vicinity and showed that impaired progenitor recruitment alters sexual maturation.In a second study, we evaluated whether cell neogenesis still occurs during adulthood in hypothalamic regions relevant for the reproductive function. Our results showed that new cells are born in the POA of adult female rats. The rate of cell neogenesis varies across the estrus cycle, suggesting a regulatory influence of gonadal steroids. Moreover, we showed that gestation impacts the rate of cell neogenesis in a POA region implicated in the control of maternal behavior.While cell neogenesis in the adult hypothalamus has been mainly studied in laboratory rodents, it remains to be known whether this phenomenon also occurs in humans. To start addressing this question, we evaluated in a third study the expression of a panel of NPC markers in the adult human hypothalamus and compared it to that found in rodents (mouse, rat) and a lemur primate, the grey mouse lemur. Our results showed that the adult human hypothalamus contains populations of cells with an antigenic profile of NPC, some of which appear specific to humans.Altogether, this work shows that new cells are born in hypothalamic regions controlling reproduction throughout postnatal and adult life in female rats, and that this process is required for sexual maturation. The identification of NPC marker-expressing cells in the adult human hypothalamus suggests that the capacity for cell neogenesis also exists in the hypothalamus of our species.

Spleen is the largest secondary lymphatic organ which develops in a short postnatal period. Information on postnatal development of rabbit spleen is minimal in available literary sources. This diploma thesis deals with the weight, morphometric and histological changes of the spleen of rabbits at age 0, 5, 10, 14, 19, 27, 32 and 39 days. During postnatal development of rabbits, a statistically significant (P <0.01) increase in the weight, length and width of the spleen occurred. The spleen of newborn rabbits was a relatively small organ with an average length of 1.03?0.12 cm, a width of 0.2?0.01 cm and a weight of 52.50?9.69 g. At age 39 days the size and shape of spleen of adult individuals (average length 4.97?0.73 cm, width 0.9?0.18 cm and weight 1078.40?143.35 g). Between the weight and morphometric parameters, high correlation coefficients were observed in the range of 0.891 to 0.998. Spleen growth was accompanied by increasing cellularisation of the parenchyma, by strengthening the connective tissue (from 8.04?1.50 m to 31.30?5.51 m) and the progressive occurrence of connective tissue in the parenchyma. In the newborn rabbits, a red pulp with a high level of erythrocytes prevailed in the spleen parenchyma. Lymphatic tissue consisted only of small irregular aggregations of basophilic mononuclear cells around several central arteries. Basophilic and vascularization increased in the course of the age and the white pulp was gradually formed. In 14 day rabbits, the marginal zone was well-known, and primary lymph nodes formed by CD79+ cells were first formed. From 14th to 39th day the spleen gradually increased the frequency and size of the individual compartments, with rare germinal centers observed in the lymph nodes until the 39th day. Throughout the course of the observation, extramedullary haematopoiesis of different intensity was seen in the spleen.

Dans cette étude, nous avons utilisé un modèle de souris permettant d’induire des lésions de sévérité variable afin de mimer différentes anomalies de la myéline du cerveau que l'on peut rencontrer chez l'homme. La perte des OLs a été de 80% après 2 semaines de traitement au GCV (GCV1-14). Après l'arrêt du traitement, les processus de récupération ont conduit à une augmentation significative de la population OLs à 80% à la semaine 6 (W6). L’extension du traitement GCV à 3 semaines (GCV1-21) a entraîné une perte de 85% de la population OLs. Cependant la récupération est limitée et reste à 40% du niveau de contrôle à W6. Nous avons remarqué une augmentation rapide (de 2 fois) des cellules Olig2+ chez la souris GCV1-14 contre les souris GCV1-21 (de 1,5 fois) à W4. Nos résultats ont montré une augmentation significative des cellules Olig2-phosphorylé chez la souris GCV1-14 entre W3 et W4 après l'arrêt du traitement GCV. A l'opposé, dans le modèle GCV1-21, un très faible niveau de Olig2 phosphorylé a été observé. Nous avons observé des modifications transitoires dans l’expression de NgR et Caspr mais l’expression de P75 reste inchangée. Ensemble, ces résultats suggèrent que la reprise du déficit myéline du cerveau au cours du développement postnatal dépend de régénération suffisante des oligodendrocytes dans un laps de temps défini pour la myélinisation normale. / Abnormalities of myelination during brain development are thought to result in neurologic and psychiatric disorders. We tested the developmental time window required for oligodendrocyte generation and myelin formation in the central nervous system, using a transgenic mouse harboring HSV1-TK and eGFP genes under the control of MBP and PLP promoters respectively, to carry out the conditional ablation of oligodendrocytes. The first ablation program comprised daily injection of ganciclovir (GCV) for two weeks (GCV1-14) to induce a reversible myelin recovery. The second program comprised GCV injection for 3 weeks (GCV1-21) to create a model of irreversible myelin recovery. GCV1-14 model presented 85% reduction of oligodendrocytes at week 2 (W2) and significantly increased recovery of oligodendrocytes and myelin at W4, then slower recuperation in the following weeks after the arrest of GCV treatment. Similarly, GCV treatment for three weeks (GCV1-21) induced severe deficiency of oligodrndocytes (90%) and myelin at W3. Contrasting the GCV1-14 program, only 40-50% of oligodendrocyte population was recovered at W6 and brain remained severely deficient in myelin. Moreover, no significant recovery was observed during the following weeks and myelin at W4, then slower recuperation in the following weeks after the arrest of GCV treatment. Similarly, GCV treatment for three weeks (GCV1-21) induced severe deficiency of oligodrndocytes (90%) and myelin at W3. Contrasting the GCV1-14 program, only 40-50% of oligodendrocyte population was recovered at W6 and brain remained severely deficient in myelin. Moreover, no significant recovery was observed during the following weeks and frequently ended with premature death of mice. Since no significant changes in the expression of axonal markers including neurofilaments, NgR, P75, Caspr and neurofascin186 were detected at W5 in the two models, we conclude that an intrinsic defect of oligodendrocyte regeneration at W3-W4 underlies the irreversible model. Significant number of phosphorylated Olig2+ cells was observed at W3 in reversible model in demyelinated corpus callosum while at the same time-point, this population is absent from control and irreversible model. At the same period, the proliferation index (Ki67) of Olig2+ cells is 8 fold higher in the corpus callosum of GCV1-14 model than the control and the irreversible model. Together, these findings suggest that recovery from myelin deficit during postnatal brain development depends on sufficient regeneration of oligodendrocytes within a defined time frame for normal myelination to occur.

Les cellules microgliales constituent la population de macrophages résidents du système nerveux central. De par leur appartenance au système immunitaire, elles furent longtemps considérées actives uniquement en conditions pathologiques. Au contraire, ces dernières décennies, elles sont apparues comme physiologiquement actives, notamment au cours de la période critique de formation du système nerveux central. Au cours du développement embryonnaire et postnatal, les neurones nouvellement générés migrent vers leur position définitive avant de développer leur arbre dendritique et axonal afin de former les connexions synaptiques à la base des réseaux nécessaires aux fonctions cérébrales. L'étude des microglies au cours de la période postnatale, a montré l'implication d'un mode de communication spécifique entre les neurones et la microglie, la voie Fractalkine/CX3CR1, dans la mise en place des cellules microgliales d'une part et dans le développement synaptique glutamatergique d'autre part. Cependant, l'importance de cette communication neurone-microglie pour le développement du système inhibiteur GABAergique est peu connue. Au cours de mon travail de thèse, je me suis intéressée au rôle de la voie de communication FractalKine/CX3CR1 dans la distribution des cellules microgliales et le développement postnatal du réseau GABAergique de l'Hippocampe. Nous avons ainsi montré que la suppression du récepteur microglial CX3CR1 induit une diminution du nombre de microglies dans la région CA3 de l'Hippocampe, dans une fenêtre temporelle précise entre 7 et 2 jours après la naissance. Cette diminution du nombre de microglies est corrélée avec une altération de l'activité de réseau au niveau de cette région. En effet, la fréquence des GDPs (Giant Depolarizing Potentials), une activité de réseau impliquée dans la formation et la maturation des synapses et spécifiquement générée en CA3, est diminuée à la fin de la première semaine postnatale. De plus, malgré l'absence de modification majeure de l'activité synaptique glutamatergique et GABAergique, les évènements postsynaptiques GABAergiques présentent une sous population d'évènements plus amples et des cinétiques légèrement plus rapides, pouvant suggérer une modification de la population d'interneurones mis en jeu. L'ensemble de mon travail de thèse met en évidence l'impact de la communication neurone-microglie par la voie Fractalkine/CX3CR1 sur le développement postnatal de l'Hippocampe Son absence affecte d'une part, la colonisation microgliale, et d'autre part, une activité de réseau caractéristique de l'Hippocampe, dans une fenêtre temporelle critique pour la mise en place des connexions synaptiques et la formation des réseaux neuronaux . / Microglial cells, the resident macrophages of the central nervous system, were mainly studied for their role in pathological conditions, but they recently appeared to be involved in synaptic development and circuits formation during postnatal period. During this critical period, microglial cells colonize the central nervous system and interact with other cell types, including neurons. A specific way of communication between neurons and microglia involves neuronal released fractalkine (CX3CL1) and its specific microglial receptor CX3CR1. CX3CR1 KO mice contributed to unclose microglial role during development. Indeed, CX3CR1 ablation alters microglia distribution in the brain, and it affects glutamatergic transmission and synapse maturation. However, these effects seem to be transient and brain region specific and their mechanisms are poorly understood. Furthermore, some effects observed in juvenile or adult mice may have origin during development, when neuronal connections are established. GABA plays a fundamental role in this process since it is excitatory The influence of neuron.microglia interaction on neuronal activity in the hippocampus during this period is poorly understood. In particular, nothing is known on GABAergic activity, known to be synaptogenic during this period My PhD project aimed at investigating how the signaling fractalkine pathway impacts microglial coloniation of the hippocampus and neuronal activity during the first two postnatal weeks. Our results indicate that in CX3XR1KO mice there is a reduction in the density of microglial cells at P7-P9 in the CA3 hippocampal area, accompanied at P7 by a significant reduction of frequency of Giant Depolarizing Potentials (GDPs), a network activity involved in hippocampal synapse formation and maturation Furthermore, despite no overall difference in glutamatergic or GABAergic synaptic activity, GABAergic events display a subpopulation of larger events, and the kinetics was slightly faster. Thus, the disruption of the specific neuronal.microglia signaling pathway on one hand impacts the microglia coloniation of the hippocampus and on the other hands affects specifically neuronal network activity during a time window critical for the establishment of neuronal connections.

Les premières semaines postnatales sont essentielles pour le développement de la sensibilité à la douleur et sont associées à une réorganisation structurelle et fonctionnelle des systèmes sensoriels. Les interneurones localisés dans la couche II interne (IIi) du sous noyau caudal du trijumeau (Sp5C), premier relais de l’information tactile et nociceptive orofaciale, sont des éléments clés des circuits responsables de l’allodynie mécanique orofaciale. L’objectif de ce travail de thèse est d’étudier le développement postnatal, à la fois morphologique (en utilisant l’immunohistochimie et l’analyse morphologique tridimensionnelle) et fonctionnel (enregistrements en patch-clamp sur tranches de Sp5C), de ces interneurones. Nous nous sommes d’abord intéressés à une population très particulière d’interneurones de la couche IIi, qui expriment l’isoforme gamma de la protéine kinase C (PKCγ). Au stade le plus précoce de notre étude (3 jours postnataux, P3), les interneurones PKCγ sont présents dans toutes les couches superficielles sauf, précisément, la couche IIi. Ce n’est qu’à P6 que les premiers interneurones PKCγ peuvent être observés dans cette couche. Leur nombre y croît ensuite progressivement jusqu’à P11-15. A cet âge, leur nombre dans la couche IIi est quasiment identique à celui observé aux âges plus tardifs. De plus, nous montrons que cette augmentation du nombre d’interneurones PKCγ dans la couche IIi n’est liée ni à une prolifération cellulaire ni à l’arrivée progressive des fibres afférentes nociceptives dans le Sp5C. Nous avons également étudié le développement des interneurones de la couche IIi dans leur ensemble. Ces neurones sont l’objet d’un grand nombre de changements morphologiques, aussi bien au niveau de leur soma (augmentation du volume) que de leurs neurites (augmentation de leur longueur combinée à une diminution de leur nombre et de leurs ramifications). Sur le plan fonctionnel, les neurones de la couche IIi, à la naissance, sont plus dépolarisés, ont une rhéobase plus basse – ils seraient donc plus excitables – et montrent plus fréquemment un profil de décharge avec un seul potentiel d’action, comparés aux mêmes interneurones chez l’adulte.Toutes ces modifications structurelles et fonctionnelles des interneurones de la couche IIi du Sp5C pourraient contribuer au développement de la sensibilité orofaciale. / The first postnatal weeks are pivotal for the development of pain sensitivity and are associated with structural and functional reorganization of sensory systems. Interneurons located in the inner part of lamina II(IIi) of the caudal trigeminal subnucleus (Sp5C), the first central node in orofacial tactile and nociceptive pathways, are key elements in circuits underlying the orofacial mechanical allodynia. The aim of this thesis is to study the morphological (by using immunohistochemistry and tridimensional morphological analysis) and functional (by using whole-cell patch-clamp recordings) postnatal development of these interneurons. First, we looked at a very specific population of lamina IIi interneurons expressing the gamma isoform of the protein kinase C (PKCγ). At the earliest stage of our study (3 postnatal days, P3), PKCγ interneurons are present in all superficial layers but PKCγ interneurons can be observed in lamina IIi only at P6. The number of PKCγ interneurons within this lamina then increases gradually up to P11-15. At this age, the number of PKCγ interneurons in lamina IIi is almost the same as that at later ages. Interestingly, we show that neither cell proliferation nor the gradual projection of nociceptive fibers within the Sp5C accounts for such increase. We also studied the development of the whole population of lamina IIi interneurons. These interneurons undergo a large number of morphological changes, in their soma (increased volume) as well as neurites (concomitant increase in length and decrease in number and branching). Furthermore, according to electrophysiological properties, lamina IIi interneurons, at birth, are more depolarized, have a lower rheobase – suggesting that they are more excitable – and exhibit more frequently a single action potential discharge profile compared with mature ones. All these structural and functional changes of lamina IIi interneurons might contribute to the development of orofacial sensitivity.

No description available.

Fructose-2, 6-bisphosphate (fru-2, 6P2), synthesized by 6-phosphofructo-2-kinase (PFK2), regulates glucose metabolism via modulating phosphofructokinase-1 (PFK1) and fructose-1, 6-bisphosphatase (FBPase1) reciprocally in mammalian tissues. How this control system develops in brain is poorly understood. This article presents the postnatal comparative profiles of fru-2, 6P2 and PFK2 & fru-2, 6P2 dependent regulation of PFK1 and FBPase1 in mice brain. Fru-2, 6P2 and PFK2 activity both attained their adult levels in concordance from day1 to 1wk age. Western blot analysis of mice liver and brain & rat liver PFK2 using anti rat liver PFK2/FBPase2 confirmed that both, mice liver and brain isoforms cross- react efficiently with this antibody. In addition, DEAE-eluted brain fractions from different postnatal ages revealed that 1day mice brain expresses a liver type enzyme (∼55 kDa) that is replaced by an adult brain type protein (∼110 kDa) from 1wk onward ages. As compared to 1day mice, significantly decreased Km values of PFK2 at 1wk-10wk ages also suggest the existence of a kinetically different isoform of this enzyme from 1wk onward ages. In vitro effects of fru-2, 6P2 on partially enriched brain PFK1 and FBPase1 suggest that fru-2, 6P2 dependent respective stimulatory and inhibitory responses of both these enzymes increase progressively from day1 to 3wk age. This is well corroborated with the postnatal age-dependent linear increase in PFK1 and decrease in FBPase1 activities in mice brain. The results suggest that fru-2, 6P2 associated regulatory components develop in concordance in mice brain during early postnatal life.

No description available.

Treatments for skeletal tissue injuries include surgery and rehabilitation but in adult patients, the healing process is slow and incomplete, and the underlying biological mechanisms are largely unknown. Skeletal tissues contain stem cells responsible for their maintenance and repair, but the identity and location of these stem cells, and what molecular mechanisms regulate their fate decisions remain unclear. To design more effective regenerative therapies for skeletal conditions, understanding the fundamental biology of skeletal stem cells (SSC) in postnatal organisms is required. Our project aims at identifying and characterizing these SSC populations in postnatal murine and human tissues using lineage tracing techniques, combined with multicolor 3D confocal microscopy and computational image analysis, in vitro assays, and single cell transcriptomics. We hypothesized that the postnatal skeleton contains self-renewing and multipotent Sox9+ SSCs that persist in adulthood. We showed that the adult mouse skeleton contains Sox9+ cells self-renewing, multipotent skeletal stem cells (SSCs) with osteogenic and chondrogenic potential. They are located adjacent to the growth plates and in periosteum and persist in adulthood. Transcriptome analysis revealed that these cells express other putative SSCs markers, as well as genes involved in skeletal development, stem cell self-renewal, and fate decision. This data provides testable drug targets to pharmacologically manipulate SSCs fate decisions in situ. In addition, we showed that human tissues contain SSCs similar to murine tissues. This is the first experimental proof of self-renewal in postnatal Sox9+ SSCs in vivo. These findings provide actionable insights for the use of culture-expanded stem cell product for regenerative medicine product or pharmacological targeting of these stem cells in situ. We believe our data will help improve stem-cell based and tissue engineering therapies, increasing success rate of regenerative orthopaedic surgeries while reducing reoccurrence of injuries.