Evolution of gene expression across brain regions in behaviourally divergent deer mice.

The evolution of innate behaviours is ultimately due to genetic variation likely acting in the nervous system. Gene regulation may be particularly important because it can evolve in a modular brain-region specific fashion through the concerted action of cis- and trans-regulatory changes. Here, to investigate transcriptional variation and its regulatory basis across the brain, we perform RNA sequencing (RNA-Seq) on ten brain subregions in two sister species of deer mice (Peromyscus maniculatus and P. polionotus)-which differ in a range of innate behaviours, including their social system-and their F1 hybrids. We find that most of the variation in gene expression distinguishes subregions, followed by species. Interspecific differential expression (DE) is pervasive (52-59% of expressed genes), whereas the number of DE genes between sexes is modest overall (~3%). Interestingly, the identity of DE genes varies considerably across brain regions. Much of this modularity is due to cis-regulatory divergence, and while 43% of genes were consistently assigned to the same gene regulatory class across subregions (e.g. conserved, cis- or trans-regulatory divergence), a similar number were assigned to two or more different gene regulatory classes. Together, these results highlight the modularity of gene expression differences and divergence in the brain, which may be key to explain how the evolution of brain gene expression can contribute to the astonishing diversity of animal behaviours.

Congenital Upper-Limb Differences: A 6-Year Literature Review.

➤ The Oberg-Manske-Tonkin (OMT) classification of congenital hand and upper-limb anomalies continues to be refined as our understanding of the genetic and embryonic etiology of limb anomalies improves.➤ We have conducted an evaluation of graft and graftless techniques for syndactyly reconstruction; strengths and drawbacks exist for each technique.➤ Treatment for radial longitudinal deficiency remains controversial; however, radialization has shown promise in early follow-up for severe deformities.➤ Recent emphasis on psychosocial aspects of care has demonstrated that children with congenital upper-limb differences demonstrate good peer relationships and marked adaptability.

Chronic nicotine impairs the angiogenic capacity of human induced pluripotent stem cell-derived endothelial cells in a murine model of peripheral arterial disease.

Objective: Lifestyle choices such as tobacco and e-cigarette use are a risk factor for peripheral arterial disease (PAD) and may influence therapeutic outcomes. The effect of chronic nicotine exposure on the angiogenic capacity of human induced pluripotent stem cell-derived endothelial cells (iPSC-ECs) was assessed in a murine model of PAD. Methods: Mice were exposed to nicotine or phosphate-buffered saline (PBS) for 28 days, followed by induction of limb ischemia and iPSC-EC transplantation. Cells were injected into the ischemic limb immediately after induction of hindlimb ischemia and again 7 days later. Limb perfusion was assessed by laser Doppler spectroscopy, and transplant cell survival was monitored for 14 days afterward using bioluminescence imaging, followed by histological analysis of angiogenesis. Results: Transplant cell retention progressively decreased over time after implantation based on bioluminescence imaging, and there were no significant differences in cell survival between mice with chronic exposure to nicotine or PBS. However, compared with mice without nicotine exposure, mice with prior nicotine exposure had had an impaired therapeutic response to iPSC-EC therapy based on decreased vascular perfusion recovery. Mice with nicotine exposure, followed by cell transplantation, had significantly lower mean perfusion ratio after 14 days (0.47 ± 0.07) compared with mice undergoing cell transplantation without prior nicotine exposure (0.79 ± 0.11). This finding was further supported by histological analysis of capillary density, in which animals with prior nicotine exposure had a lower capillary density (45.9 ± 4.7 per mm2) compared with mice without nicotine exposure (66.5 ± 8.1 per mm2). Importantly, the ischemic limbs mice exposed to nicotine without cell therapy also showed significant impairment in perfusion recovery after 14 days, compared with mice that received PBS + iPSC-EC treatment. This result suggested that mice without chronic nicotine exposure could respond to iPSC-EC implantation into the ischemic limb by inducing perfusion recovery, whereas mice with chronic nicotine exposure did not respond to iPSC-EC therapy. Conclusions: Together, these findings show that chronic nicotine exposure adversely affects the ability of iPSC-EC therapy to promote vascular perfusion recovery and angiogenesis in a murine PAD model.

A single genetic locus lengthens deer mouse burrows via motor pattern evolution.

The question of how evolution builds complex behaviors has long fascinated biologists. To address this question from a genetic perspective, we capitalize on variation in innate burrowing behavior between two sister species of Peromyscus mice: P. maniculatus that construct short, simple burrows and P. polionotus that uniquely construct long, elaborate burrows. We identify three regions of the genome associated with differences in burrow length and then narrow in on one large-effect 12-Mb locus on chromosome 4. By introgressing the P. polionotus allele into a P. maniculatus background, we demonstrate this locus, on its own, increases burrow length by 20%. Next, by recording mice digging in a transparent tube, we find this locus has specific effects on burrowing behavior. This locus does not affect time spent digging or latency to dig, but rather affects usage of only two of the primary digging behaviors that differ between the focal species: forelimb digging, which loosens substrate, and hindlimb kicking, which powerfully ejects substrate. This locus has an especially large effect on hindkicking, explaining 56% and 22% of interspecific differences in latency and proportion of hindkicks, respectively. Together, these data provide genetic support for the hierarchical organization of complex behaviors, offering evolution the opportunity to tinker with specific behavioral components.

Elastin-like protein hydrogels with controllable stress relaxation rate and stiffness modulate endothelial cell function.

Mechanical cues from the extracellular matrix (ECM) regulate vascular endothelial cell (EC) morphology and function. Since naturally derived ECMs are viscoelastic, cells respond to viscoelastic matrices that exhibit stress relaxation, in which a cell-applied force results in matrix remodeling. To decouple the effects of stress relaxation rate from substrate stiffness on EC behavior, we engineered elastin-like protein (ELP) hydrogels in which dynamic covalent chemistry (DCC) was used to crosslink hydrazine-modified ELP (ELP-HYD) and aldehyde/benzaldehyde-modified polyethylene glycol (PEG-ALD/PEG-BZA). The reversible DCC crosslinks in ELP-PEG hydrogels create a matrix with independently tunable stiffness and stress relaxation rate. By formulating fast-relaxing or slow-relaxing hydrogels with a range of stiffness (500-3300 Pa), we examined the effect of these mechanical properties on EC spreading, proliferation, vascular sprouting, and vascularization. The results show that both stress relaxation rate and stiffness modulate endothelial spreading on two-dimensional substrates, on which ECs exhibited greater cell spreading on fast-relaxing hydrogels up through 3 days, compared with slow-relaxing hydrogels at the same stiffness. In three-dimensional hydrogels encapsulating ECs and fibroblasts in coculture, the fast-relaxing, low-stiffness hydrogels produced the widest vascular sprouts, a measure of vessel maturity. This finding was validated in a murine subcutaneous implantation model, in which the fast-relaxing, low-stiffness hydrogel produced significantly more vascularization compared with the slow-relaxing, low-stiffness hydrogel. Together, these results suggest that both stress relaxation rate and stiffness modulate endothelial behavior, and that the fast-relaxing, low-stiffness hydrogels supported the highest capillary density in vivo.

Do Nails and Nubbins Matter? A Comparison of Symbrachydactyly and Transverse Deficiency Phenotypes.

PURPOSE: Transverse deficiency (TD) and symbrachydactyly may be difficult to distinguish due to shared phenotypes and a lack of pathognomonic features. The 2020 Oberg-Manske-Tonkin classification update modified these anomalies to include "with ectodermal elements" for symbrachydactyly and "without ectodermal elements" for TD as a defining differentiating characteristic. The purpose of this investigation was to characterize ectodermal elements and the level of deficiency and to examine whether ectodermal elements versus the level of deficiency was a greater determining factor for Congenital Upper Limb Differences (CoULD) surgeons making the diagnosis. METHODS: This was a retrospective review of 254 extremities from the CoULD registry with a diagnosis of symbrachydactyly or TD by pediatric hand surgeons. Ectodermal elements and the level of deficiency were characterized. A review of the registry radiographs and photographs was used to classify the diagnosis and compare it with the diagnosis given by the pediatric hand surgeons. The presence/absence of nubbins versus the level of deficiency as the determining factor to differentiate the pediatric hand surgeons' diagnosis of symbrachydactyly (with nubbins) versus TD (without nubbins) was analyzed. RESULTS: Based on radiographs and photographs of the 254 extremities, 66% had nubbins on the distal end of the limb; of the limbs with nubbins, nails were present on 51%. The level of deficiency was amelia/humeral (n = 9), <1/3 transverse forearm (n = 23), 1/3 to 2/3 transverse forearm (n = 27), 2/3 to full forearm TD (n = 38), and metacarpal/phalangeal (n = 103). The presence of nubbins was associated with a four times higher likelihood of a pediatric hand surgeon's diagnosis of symbrachydactyly. However, a distal deficiency is associated with a 20-times higher likelihood of a diagnosis of symbrachydactyly than a proximal deficiency. CONCLUSIONS: Although both the level of deficiency and ectodermal elements are important, the level of deficiency was a greater determining factor for a diagnosis of symbrachydactyly versus TD. Our results suggest that the level of deficiency and nubbins should both be described to help provide greater clarity in the diagnosis of symbrachydactyly versus TD. TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic IV.

Infection from an Iliosacral Screw 16 Years Postoperatively in Demolition Derby Umpire Crushed Between 2 Cars: A Case Report.

CASE: A 47-year-old man crushed between 2 cars during a demolition derby, a nonracing North American motorsport, underwent open reduction and internal fixation, iliosacral screw fixation, arterial embolization, and multiple urologic procedures after massive pelvic ring injury, remarkably recovering nearly full function. Sixteen years after injury, he developed an abscess emanating from an iliosacral screw requiring irrigation, debridement, and hardware removal. CONCLUSION: Deep surgical infections from iliosacral screws may present late, even more than 15 years after the original surgery. Obesity, preoperative embolization, diabetes, and urethral injuries are relevant risk factors. Similar patients should have a low threshold for infection workup when presenting with symptoms, even years after surgery.

Scalable macroporous hydrogels enhance stem cell treatment of volumetric muscle loss.

Volumetric muscle loss (VML), characterized by an irreversible loss of skeletal muscle due to trauma or surgery, is accompanied by severe functional impairment and long-term disability. Tissue engineering strategies combining stem cells and biomaterials hold great promise for skeletal muscle regeneration. However, scaffolds, including decellularized extracellular matrix (dECM), hydrogels, and electrospun fibers, used for VML applications generally lack macroporosity. As a result, the scaffolds used typically delay host cell infiltration, transplanted cell proliferation, and new tissue formation. To overcome these limitations, we engineered a macroporous dECM-methacrylate (dECM-MA) hydrogel, which we will refer to as a dECM-MA sponge, and investigated its therapeutic potential in vivo. Our results demonstrate that dECM-MA sponges promoted early cellularization, endothelialization, and establishment of a pro-regenerative immune microenvironment in a mouse VML model. In addition, dECM-MA sponges enhanced the proliferation of transplanted primary muscle stem cells, muscle tissue regeneration, and functional recovery four weeks after implantation. Finally, we investigated the scale-up potential of our scaffolds using a rat VML model and found that dECM-MA sponges significantly improved transplanted cell proliferation and muscle regeneration compared to conventional dECM scaffolds. Together, these results validate macroporous hydrogels as novel scaffolds for VML treatment and skeletal muscle regeneration.

cis-Regulatory changes in locomotor genes are associated with the evolution of burrowing behavior.

How evolution modifies complex, innate behaviors is largely unknown. Divergence in many morphological traits, and some behaviors, is linked to cis-regulatory changes in gene expression. Given this, we compare brain gene expression of two interfertile sister species of Peromyscus mice that show large and heritable differences in burrowing behavior. Species-level differential expression and allele-specific expression in F1 hybrids indicate a preponderance of cis-regulatory divergence, including many genes whose cis-regulation is affected by burrowing behavior. Genes related to locomotor coordination show the strongest signals of lineage-specific selection on burrowing-induced cis-regulatory changes. Furthermore, genetic markers closest to these candidate genes associate with variation in burrow shape in a genetic cross, suggesting an enrichment for loci affecting burrowing behavior near these candidate locomotor genes. Our results provide insight into how cis-regulated gene expression can depend on behavioral context and how this dynamic regulatory divergence between species may contribute to behavioral evolution.

Comparative Effects of Basic Fibroblast Growth Factor Delivery or Voluntary Exercise on Muscle Regeneration after Volumetric Muscle Loss.

Volumetric muscle loss (VML) is associated with irreversibly impaired muscle function due to traumatic injury. Experimental approaches to treat VML include the delivery of basic fibroblast growth factor (bFGF) or rehabilitative exercise. The objective of this study was to compare the effects of spatially nanopatterned collagen scaffold implants with either bFGF delivery or in conjunction with voluntary exercise. Aligned nanofibrillar collagen scaffold bundles were adsorbed with bFGF, and the bioactivity of bFGF-laden scaffolds was examined by skeletal myoblast or endothelial cell proliferation. The therapeutic efficacy of scaffold implants with either bFGF release or exercise was examined in a murine VML model. Our results show an initial burst release of bFGF from the scaffolds, followed by a slower release over 21 days. The released bFGF induced myoblast and endothelial cell proliferation in vitro. After 3 weeks of implantation in a mouse VML model, twitch force generation was significantly higher in mice treated with bFGF-laden scaffolds compared to bFGF-laden scaffolds with exercise. However, myofiber density was not significantly improved with bFGF scaffolds or voluntary exercise. In contrast, the scaffold implant with exercise induced more re-innervation than all other groups. These results highlight the differential effects of bFGF and exercise on muscle regeneration.

peri-Adventitial delivery of smooth muscle cells in porous collagen scaffolds for treatment of experimental abdominal aortic aneurysm.

Abdominal aortic aneurysm (AAA) is associated with the loss of vascular smooth muscle cells (SMCs) within the vessel wall. Direct delivery of therapeutic cells is challenging due to impaired mechanical integrity of the vessel wall. We hypothesized that porous collagen scaffolds can be an effective vehicle for the delivery of human-derived SMCs to the site of AAA. The purpose was to evaluate if the delivery of cell-seeded scaffolds can abrogate progressive expansion in a mouse model of AAA. Collagen scaffolds seeded with either primary human aortic SMCs or induced pluripotent stem cell derived-smooth muscle progenitor cells (iPSC-SMPs) had >80% in vitro cell viability and >75% cell penetrance through the scaffold's depth, while preserving smooth muscle phenotype. The cell-seeded scaffolds were successfully transplanted onto the murine aneurysm peri-adventitia on day 7 following AAA induction using pancreatic porcine elastase infusion. Ultrasound imaging revealed that SMC-seeded scaffolds significantly reduced the aortic diameter by 28 days, compared to scaffolds seeded with iPSC-SMPs or without cells (acellular scaffold), respectively. Bioluminescence imaging demonstrated that both cell-seeded scaffold groups had cellular localization to the aneurysm but a decline in survival with time. Histological analysis revealed that both cell-seeded scaffold groups had more SMC retention and less macrophage invasion into the medial layer of AAA lesions, when compared to the acellular scaffold treatment group. Our data suggest that scaffold-based SMC delivery is feasible and may constitute a platform for cell-based AAA therapy.

A Comparative Analysis of 150 Thumb Polydactyly Cases from the CoULD Registry Using the Wassel-Flatt, Rotterdam, and Chung Classifications.

PURPOSE: Three commonly used classifications for thumb polydactyly are the Wassel-Flatt, Rotterdam, and Chung. The ideal classification system would have high validity and reliability and be descriptive of the thumb anomaly. The purposes of this investigation were to (1) compare the inter- and intrarater reliability of these 3 classifications when applied to a large sample of patients enrolled in the Congenital Upper Limb Differences (CoULD) Registry and (2) determine the prevalence of radial polydactyly types when using the various classifications in a North American population. METHODS: Inter- and intrarater reliability were determined using 150 cases of radial polydactyly presented in a Web-based format to 7 raters in 3 rounds, a preliminary training round and 2 observation rounds. Raters classified each case according to the Wassel-Flatt, Rotterdam, and Chung classifications. Inter- and intrarater reliability were evaluated with the intraclass correlation coefficient (ICC) calculated using 2-way random measures with perfect agreement. RESULTS: For Wassel-Flatt, both the interrater (ICC, 0.93) and the intrarater reliability (ICC, 0.91) were excellent. The Rotterdam classification had excellent reliability for both interrater reliability (ICC, 0.98) and intrarater reliability (ICC, 0.94), when considering type alone. Interrater analysis of the additional subtypes demonstrated a wide range of reliabilities. The Chung classification had good interrater (ICC, 0.88) and intrarater reliability (ICC, 0.77). Within the Wassel-Flatt classification, the most frequent unclassifiable thumb was a type IV hypoplastic thumb as classified by the Rotterdam classification. CONCLUSIONS: The Wassel-Flatt and Rotterdam classifications for radial polydactyly have excellent inter- and intrarater reliability. Despite its simplicity, the Chung classification was less reliable in comparison. The Chung and Rotterdam classification systems capture the hypoplastic subtypes that are unclassifiable in the Wassel-Flatt system. Addition of the hypoplastic subtype to the Wassel-Flatt classification (eg, Wassel-Flatt type IVh) would maintain the highest reliability and classify over 90% of thumbs deemed unclassifiable in the Wassel-Flatt system. CLINICAL RELEVANCE: The Wassel-Flatt and Rotterdam classifications have excellent inter-and intrarater reliability for the hand surgeon treating thumb polydactyly. Addition of a hypoplastic subtype to the Wassel-Flatt (Type 4h) allows classification of most previously unclassifiable thumbs.

Transplantation of insulin-like growth factor-1 laden scaffolds combined with exercise promotes neuroregeneration and angiogenesis in a preclinical muscle injury model.

The regeneration of skeletal muscle can be permanently impaired by traumatic injuries, despite the high regenerative capacity of native muscle. An attractive therapeutic approach for treating severe muscle inuries is the implantation of off-the-shelf engineered biomimetic scaffolds into the site of tissue damage to enhance muscle regeneration. Anisotropic nanofibrillar scaffolds provide spatial patterning cues to create organized myofibers, and growth factors such as insulin-like growth factor-1 (IGF-1) are potent inducers of both muscle regeneration as well as angiogenesis. The aim of this study was to test the therapeutic efficacy of anisotropic IGF-1-releasing collagen scaffolds combined with voluntary exercise for the treatment of acute volumetric muscle loss, with a focus on histomorphological effects. To enhance the angiogenic and regenerative potential of injured murine skeletal muscle, IGF-1-laden nanofibrillar scaffolds with aligned topography were fabricated using a shear-mediated extrusion approach, followed by growth factor adsorption. Individual scaffolds released a cumulative total of 1244 ng ± 153 ng of IGF-1 over the course of 21 days in vitro. To test the bioactivity of IGF-1-releasing scaffolds, the myotube formation capacity of murine myoblasts was quantified. On IGF-1-releasing scaffolds seeded with myoblasts, the resulting myotubes formed were 1.5-fold longer in length and contained 2-fold greater nuclei per myotube, when compared to scaffolds without IGF-1. When implanted into the ablated murine tibialis anterior muscle, the IGF-1-laden scaffolds, in conjunction with voluntary wheel running, significantly increased the density of perfused microvessels by greater than 3-fold, in comparison to treatment with scaffolds without IGF-1. Enhanced myogenesis was also observed in animals treated with the IGF-1-laden scaffolds combined with exercise, compared to control scaffolds transplanted into mice that did not receive exercise. Furthermore, the abundance of mature neuromuscular junctions was greater by approximately 2-fold in muscles treated with IGF-1-laden scaffolds, when paired with exercise, in comparison to the same treatment without exercise. These findings demonstrate that voluntary exercise improves the regenerative effect of growth factor-laden scaffolds by augmenting neurovascular regeneration, and have important translational implications in the design of off-the-shelf therapeutics for the treatment of traumatic muscle injury.

Delivery of Human Stromal Vascular Fraction Cells on Nanofibrillar Scaffolds for Treatment of Peripheral Arterial Disease.

Cell therapy for treatment of peripheral arterial disease (PAD) is a promising approach but is limited by poor cell survival when cells are delivered using saline. The objective of this study was to examine the feasibility of aligned nanofibrillar scaffolds as a vehicle for the delivery of human stromal vascular fraction (SVF), and then to assess the efficacy of the cell-seeded scaffolds in a murine model of PAD. Flow cytometric analysis was performed to characterize the phenotype of SVF cells from freshly isolated lipoaspirate, as well as after attachment onto aligned nanofibrillar scaffolds. Flow cytometry results demonstrated that the SVF consisted of 33.1 ± 9.6% CD45+ cells, a small fraction of CD45-/CD31+ (4.5 ± 3.1%) and 45.4 ± 20.0% of CD45-/CD31-/CD34+ cells. Although the subpopulations of SVF did not change significantly after attachment to the aligned nanofibrillar scaffolds, protein secretion of vascular endothelial growth factor (VEGF) significantly increased by six-fold, compared to SVF cultured in suspension. Importantly, when SVF-seeded scaffolds were transplanted into immunodeficient mice with induced hindlimb ischemia, the cell-seeded scaffolds induced a significant higher mean perfusion ratio after 14 days, compared to cells delivered using saline. Together, these results show that aligned nanofibrillar scaffolds promoted cellular attachment, enhanced the secretion of VEGF from attached SVF cells, and their implantation with attached SVF cells stimulated blood perfusion recovery. These findings have important therapeutic implications for the treatment of PAD using SVF.

The Influence of Mentors in Orthopedic Surgery.

The importance of mentorship in medicine has been established. However, little is known regarding the influence of mentors in orthopedic surgery. This study sought to (1) determine the prevalence of mentoring relationships in orthopedic surgery, (2) assess the influence of mentors in specialty and subspecialty selection, and (3) evaluate the importance of gender in orthopedic mentoring relationships. An electronic survey was distributed to 358 orthopedic surgeons at academic residency programs. Participants were asked to report mentoring relationships and their attitudes toward mentors, including gender preferences. A total of 117 (95 males and 22 females) surveys were returned. The majority of respondents (66.7%, n=78) had at least one mentor in their career, and the majority of respondents (66.7%, n=52) were satisfied with their mentoring experience. Residency was the most common time to have a mentor, and 73.3% (n=44) of respondents indicated their mentor was influential in determining their subspecialty. Although only 50% of respondents indicated they had a mentor in medical school, 84.2% (n=32) believed their mentor was influential in selecting an orthopedic surgery residency. The majority (79.4%, n=62) of respondents did not have a preference on the gender of their mentor. Many orthopedic surgeons have a mentor at some point in their career who influenced their specialty or subspecialty decision. Mentoring experiences are less prevalent in medical school, and female medical students may lack accessibility to mentoring opportunities. Future efforts should focus on opportunities that connect medical students to orthopedic surgery faculty to further diversify the field and close the gender gap. [Orthopedics. 2020; 43(1):e37-e42.].

Vascularization of Engineered Spatially Patterned Myocardial Tissue Derived From Human Pluripotent Stem Cells in vivo.

Tissue engineering approaches to regenerate myocardial tissue after disease or injury is promising. Integration with the host vasculature is critical to the survival and therapeutic efficacy of engineered myocardial tissues. To create more physiologically oriented engineered myocardial tissue with organized cellular arrangements and endothelial interactions, randomly oriented or parallel-aligned microfibrous polycaprolactone scaffolds were seeded with human pluripotent stem cell-derived cardiomyocytes (iCMs) and/or endothelial cells (iECs). The resultant engineered myocardial tissues were assessed in a subcutaneous transplantation model and in a myocardial injury model to evaluate the effect of scaffold anisotropy and endothelial interactions on vascular integration of the engineered myocardial tissue. Here we demonstrated that engineered myocardial tissue composed of randomly oriented scaffolds seeded with iECs promoted the survival of iECs for up to 14 days. However, engineered myocardial tissue composed of aligned scaffolds preferentially guided the organization of host capillaries along the direction of the microfibers. In a myocardial injury model, epicardially transplanted engineered myocardial tissues composed of randomly oriented scaffolds seeded with iCMs augmented microvessel formation leading to a significantly higher arteriole density after 4 weeks, compared to engineered tissues derived from aligned scaffolds. These findings that the scaffold microtopography imparts differential effect on revascularization, in which randomly oriented scaffolds promote pro-survival and pro-angiogenic effects, and aligned scaffolds direct the formation of anisotropic vessels. These findings suggest a dominant role of scaffold topography over endothelial co-culture in modulating cellular survival, vascularization, and microvessel architecture.

Corrigendum: Commentary: Arginine Vasotocin Preprohormone Is Expressed in Surprising Regions of the Teleost Forebrain.

[This corrects the article on p. 63 in vol. 9, PMID: 29545774.].

To eat or not to eat: ontogeny of hypothalamic feeding controls and a role for leptin in modulating life-history transition in amphibian tadpoles.

Many animal life histories entail changing feeding ecology, but the molecular bases for these transitions are poorly understood. The amphibian tadpole is typically a growth and dispersal life-history stage. Tadpoles are primarily herbivorous, and they capitalize on growth opportunities to reach a minimum body size to initiate metamorphosis. During metamorphic climax, feeding declines, at which time the gastrointestinal (GI) tract remodels to accommodate the carnivorous diet of the adult frog. Here we show that anorexigenic hypothalamic feeding controls are absent in the tadpole, but develop during metamorphosis concurrent with the production of the satiety signal leptin. Before metamorphosis there is a large increase in leptin mRNA in fat tissue. Leptin receptor mRNA increased during metamorphosis in the preoptic area/hypothalamus, the key brain region involved with the control of food intake and metabolism. This corresponded with an increase in functional leptin receptor, as evidenced by induction of socs3 mRNA and phosphorylated STAT3 immunoreactivity, and suppression of feeding behaviour after injection of recombinant frog leptin. Furthermore, we found that immunoneutralization of leptin in tadpoles at metamorphic climax caused them to resume feeding. The absence of negative regulation of food intake in the tadpole allows the animal to maximize growth prior to metamorphosis. Maturation of leptin-responsive neural circuits suppresses feeding during metamorphosis to facilitate remodelling of the GI tract.