Periventricular Zone Research Articles

Sox2 Transcriptionally Regulates Pqbp1, an Intellectual Disability-Microcephaly Causative Gene, in Neural Stem Progenitor Cells

PQBP1 is a nuclear-cytoplasmic shuttling protein that is engaged in RNA metabolism and transcription. In mouse embryonic brain, our previous in situ hybridization study revealed that PQBP1 mRNA was dominantly expressed in the periventricular zone region where neural stem progenitor cells (NSPCs) are located. Because the expression patterns in NSPCs are related to the symptoms of intellectual disability and microcephaly in PQBP1 gene-mutated patients, we investigated the transcriptional regulation of PQBP1 by NSPC-specific transcription factors. We selected 132 genome sequences that matched the consensus sequence for the binding of Sox2 and POU transcription factors upstream and downstream of the mouse PQBP1 gene. We then screened the binding affinity of these sequences to Sox2-Pax6 or Sox2-Brn2 with gel mobility shift assays and found 18 genome sequences that interacted with the NSPC-specific transcription factors. Some of these sequences had cis-regulatory activities in Luciferase assays and in utero electroporation into NSPCs. Furthermore we found decreased levels of expression of PQBP1 protein in NSPCs of heterozygous Sox2-knockout mice in vivo by immunohistochemistry and western blot analysis. Collectively, these results indicated that Sox2 regulated the transcription of PQBP1 in NSPCs.

Correlation of Nr4a2 Expression with the Neuron Progenitors in Adult Zebrafish Brain

Our previous study showed that although Nr4a2b transcripts have little co-localization with tyrosine hydroxylase (TH) in the posterior tuberculum area, knockdown of Nr4a2 caused a decrease in the number of TH-positive (TH(+)) neurons in the posterior tuberculum area. It suggests that Nr4a2 expression in the progenitors may play an important role in regulating differentiation rather than survival of TH(+) progenitors in the posterior tuberculum area during early zebrafish embryogenesis. In this study, we determined the correlation between TH and Nr4a2 in adult zebrafish brain and found that Nr4a2b was co-localized with the spindle-shaped TH(+) cells in the posterior tuberculum area and some small round TH(+) cells in the pretectum area, but not with large pear-shaped TH(+) cells in adult zebrafish diencephalon. In the pretectum area, Nr4a2(+) cells were localized next to the dorsal side of TH(+) cells. Furthermore, we demonstrated that Nr4a2 was co-expressed with nestin in the progenitors of pretectum area and caudal periventricular hypothalamic zones with a lateral symmetry pattern beside the diencephalic ventricle. Co-expression of Nr4a2 and nestin in these areas was remarkably declined with aging. These findings indicate that Nr4a2 is expressed in the neuronal progenitors and plays a crucial role in the differentiation process of dopamine neuron from the stem cell. The change in Nr4a2 expression with aging suggests its possible association with neurodegenerative diseases.

Influence of long-term social interaction on chirping behavior, steroid levels and neurogenesis in weakly electric fish

Social interactions dramatically affect the brain and behavior of animals. Studies in birds and mammals indicate that socially induced changes in adult neurogenesis participate in the regulation of social behavior, but little is known about this relationship in fish. Here, we review studies in electric fish (Apteronotus leptorhychus) that link social stimulation, changes in electrocommunication behavior and adult neurogenesis in brain regions associated with electrocommunication. Compared with isolated fish, fish living in pairs have greater production of chirps, an electrocommunication signal, during dyadic interactions and in response to standardized artificial social stimuli. Social interaction also promotes neurogenesis in the periventricular zone, which contributes born cells to the prepacemaker nucleus, the brain region that regulates chirping. Both long-term chirp rate and periventricular cell addition depend on the signal dynamics (amplitude and waveform variation), modulations (chirps) and novelty of the stimuli from the partner fish. Socially elevated cortisol levels and cortisol binding to glucocorticoid receptors mediate, at least in part, the effect of social interaction on chirping behavior and brain cell addition. In a closely related electric fish (Brachyhypopomus gauderio), social interaction enhances cell proliferation specifically in brain regions for electrocommunication and only during the breeding season, when social signaling is most elaborate. Together, these studies demonstrate a consistent correlation between brain cell addition and environmentally regulated chirping behavior across many social and steroidal treatments and suggest a causal relationship.

Different Stages of White Matter Changes in the Original HDLS Family Revealed by Advanced MRI Techniques

The temporal evolution of white matter (WM) changes on MR examinations in hereditary diffuse leukoencephalopathy with spheroids (HDLS) is largely unknown. Our purpose was to investigate the evolution of these WM changes with diffusion weighted/tensor imaging (DWI/DTI) and MR Spectroscopy (MRS). A newly diagnosed patient with HDLS from the original Swedish family was followed prospectively with 5 MRI as well as DWI/DTI and MRS examinations during 16 months. The DTI eigenvalues demonstrated changes that suggested early myelin and axonal disturbances in the normal appearing WM (NAWM). DWI/DTI showed a rim of decreased diffusion progressively expanding through the WM from the initial frontal periventricular zones, and indicated complete destruction of axons and myelin in the area behind the front. MRS findings were suggestive of axonal destruction in the NAWM. We describe HDLS changes in three temporal stages of development corresponding to lesions outside, in the vicinity of, and behind a characteristic rim centrifugally progressing from the ventricular horns. The axonal disturbances indicated by MRS changes in the NAWM support a primary axonal degeneration, as proposed in the original HDLS report, rather than axonal degeneration secondary to demyelination. These findings could help in differential diagnosis of HDLS.

Using whole mount in situ hybridization to examine thyroid hormone deiodinase expression in embryonic and larval zebrafish: A tool for examining OH-BDE toxicity to early life stages

Polybrominated diphenyl ethers (PBDEs) and their oxidative metabolites (hydroxylated PBDEs; OH-BDEs) are known endocrine disrupting contaminants that have been shown to disrupt thyroid hormone regulation both in mammals and in fish. The purpose of this study was to determine the precise organ and tissue locations that express genes critical to thyroid hormone regulation in developing zebrafish (Danio rerio), and to determine the effects of an OH-BDE on their expression. While RT-PCR can provide quantitative data on gene expression, it lacks spatial sensitivity to examine localized gene expression; and, isolation of organs from zebrafish embryos is technically difficult, if not impossible. For this reason, the present study used whole mount in situ hybridization to simultaneously localize and quantify gene expression in vivo. While PBDEs and OH-BDEs have been shown to inhibit the activity and expression of deiodionases, a family of enzymes that regulate thyroid hormone concentrations intracellularly, it is unclear whether or not they can affect regional expression of the different isoforms during early development. In this study we investigated deiodinase 1 (Dio1), deiodinase 2 (Dio2), and deiodinase 3 (Dio3) mRNA expression at the following life stages (2, 8, and 1k-cells; 50%-epiboly, 6 and 18-somites, 22, 24, 48, 72 hpf and/or 10 dpf) in zebrafish and found life stage specific expression of these genes that were highly localized. To demonstrate the use of this technique for investigating potential endocrine disrupting effects, zebrafish embryos were exposed to 1, 10 and 100nM 6-OH-BDE-47. Significant increases in mean intensity of Dio1 and Dio3 expression in the periventricular zone of brain and pronephric duct, respectively (quantified by measuring intensity of coloration using ImageJ analysis software) were observed, suggesting localized response at the HPT axis with the possibility of impacting neurodevelopment. Our results demonstrate effects of OH-BDEs on thyroid regulating gene expression and provide more insight into potential sites of injury during early life stages.

γ‐Aminobutyric acid‐ρ expression in ependymal glial cells of the mouse cerebellum

The ependymal glial cells (EGCs) from the periventricular zone of the cerebellum were studied to determine their distribution and the functional properties of their γ-aminobutyric acid type A (GABA(A) ) receptors. EGCs were identified by the presence of ciliated structures on their ventricular surface and their expression of glial fibrillary acidic protein (GFAP). Interestingly, diverse cell types, including neurons, astrocytes, and other types of glia, were identified in the subventricular zone by their current profiles. Electron microscopy showed ciliated cells and myelinated axons in this zone, but we found no collateral connections to suggest the presence of functional synapses. GABA-mediated currents were recorded from EGCs in cerebellar slices from postnatal days 13 to 35 (PN13-PN35). These currents were blocked by TPMPA (a highly specific GABA(A) ρ subunit antagonist) and bicuculline (a selective antagonist for classic GABA(A) receptors). Pentobarbital failed to modulate GABA(A)-mediated currents despite the expression of GABAα1 and GABAγ2 subunits. In situ hybridization, RT-PCR, and immunofluorescence studies confirmed GABAρ1 expression in EGCs of the cerebellum. We conclude that cerebellar EGCs express GABAρ1, which is functionally involved in GABA(A) receptor-mediated responses that are unique among glial cells of the brain.

Galanin-Like Peptide (GALP) Facilitates Thermogenesis via Synthesis of Prostaglandin E2 by Astrocytes in the Periventricular Zone of the Third Ventricle

Administration of galanin-like peptide (GALP) leads to a decrease in both total food intake and body weight 24 h after injection, compared to controls. Moreover, GALP induces an increase in core body temperature. To elucidate the mechanism by which GALP exerts its effect on energy homeostasis, urethane-anesthetized rats were intracerebroventricularly injected with GALP or saline, after which oxygen consumption, heart rate, and body temperature were monitored for 4 h. In some cases, animals were also pretreated with the cyclooxygenase (COX) inhibitor, diclofenac, via intracerebroventricular (i.c.v.) or intravenous (i.v.) injection. c-Fos expression in the brain was also examined after injection of GALP, and the levels of COX and prostaglandin E(2) synthetase (PGES) mRNA in primary cultured astrocytes treated with GALP were analyzed by using qPCR. The i.c.v. injection of GALP caused biphasic thermogenesis, an effect which could be blocked by pretreatment with centrally (i.c.v.), but not peripherally (i.v.) administered diclofenac. c-Fos immunoreactivity was observed in astrocytes in the periventricular zone of the third ventricle. GALP treatment also increased COX-2 and cytosolic PGES, but not COX-1, microsomal PGES-1, or microsomal PGES-2 mRNA levels in cultured astrocytes. We, therefore, suggest that GALP elicits thermogenesis via a prostaglandin E(2)-mediated pathway in astrocytes of the central nervous system.

Social novelty enhances brain cell proliferation, cell survival, and chirp production in an electric fish, Apteronotus leptorhynchus

For many animals, enriched environments and social interaction promote adult neurogenesis. However, in some cases, the effect is transient, and long-term environmental stimuli have little benefit for neurogenesis. In electric fish, Apteronotus leptorhynchus, fish housed in pairs for 7 days show higher density of newborn brain cells (cell addition) than isolated fish, but fish paired for 14 days have rates of cell addition similar to isolated controls. We examined whether introduction of social novelty can sustain elevated levels of cell addition and prevent long-term habituation to social interaction. We also monitored electrocommunication signals ("chirps") as a measure of the behavioral response to social novelty. We paired fish for 14 days with one continuous partner (no social novelty), two sequential partners changed after 7 days (low novelty) or seven sequential partners changed every 2 days (high novelty). On Day 11, we injected fish with BrdU, sacrificed fish 3 days later and quantified BrdU labeling in the diencephalic periventricular zone. Fish exposed to no novelty had BrdU labeling similar to isolated fish. Fish with low novelty showed small increases in BrdU labeling and those with high novelty had much greater BrdU labeling. Similarly, chirp rates were greater in fish with low novelty than with no novelty and greatest yet in fish with high novelty. By varying the timing of novelty relative to BrdU injection, we showed that social novelty promoted both proliferation and survival of newborn cells. These results indicated that brain cell proliferation and survival is influenced more by social change than simply the presence of social stimuli.

Radiation of Potential Local Cancer Stem Cell Niches Improves Survival of Patients With Glioblastoma Multiforme

Radiation of Potential Local Cancer Stem Cell Niches Improves Survival of Patients With Glioblastoma Multiforme

Chronic central administration of valproic acid: Increased pro-survival phospho-proteins and growth cone associated proteins with no behavioral pathology

Valproic acid (VPA) is the most widely prescribed antiepileptic drug due to its ability to treat a broad spectrum of seizure types. However, potential complications of this drug include anticonvulsant polytherapy metabolism, organ toxicity and teratogenicity which limit its use in a variety of epilepsy patients. Direct delivery of VPA intracerebroventricularly (ICV) could circumvent the toxic effects normally seen with the oral route of administration. An additional potential benefit would be significantly reduced dosing while achieving high brain concentrations. Epileptogenic tissue from patients with intractable seizures has shown significant cell death which may be mitigated by maximizing cerebral VPA exposure. Here we show ICV administration of VPA localized to the periventricular zone increased pro-survival phospho-proteins (pAktSer473, pAktThr308, pGSK3βSer9, pErk1/2Thr202/Tyr204) and growth cone associated proteins (2G13p, GAP43) in a whole animal system. No significant changes in DCX, NeuN, synaptotagmin, and synaptophysin were detected. Assessment of possible behavioral alterations in rats receiving chronic central infusions of VPA was performed with the open field and elevated plus mazes. Neither paradigm revealed any detrimental effects of the drug infusion process.

Fenvalerate가 피라미(Zacco platypus) 뇌 조직에서 apoptosis 정도와 GFAP 발현에 미치는 영향

We evaluated the level of toxicity by LC50 and investigated the mechanism of brain impairment and GFAP expression by light and fluorescence microscopes in the pale chub, Zacco platypus, treated with fenvalerate. Survival rate was decreased according to the rise of fenvalerate concentration, and LC50 concentration was . Apoptosis was increased according to the rise of fenvalerate concentration by TUNEL assay which determine apoptotic cell death population. Also, GFAP expression was increased in the periventricular zone. These results suggest that apoptosis might be a major mechanism to brain impairment of the pale chub by fenvalrerate. Increased GFAP expression in the periventricular zone would be an index of brain impairment. Taken together, this study might contribute to reveal the pathological mechanism of fish brain impairment by insecticide of pyrethroid, and to be an useful basic data for preservation of aquatic ecosystem.

Development of the hypothalamus and pituitary in platypus (Ornithorhynchus anatinus) and short‐beaked echidna (Tachyglossus aculeatus)

The living monotremes (platypus and echidnas) are distinguished by the development of their young in a leathery-shelled egg, a low and variable body temperature and a primitive teat-less mammary gland. Their young are hatched in an immature state and must deal with the external environment, with all its challenges of hypothermia and stress, as well as sourcing nutrients from the maternal mammary gland. The Hill and Hubrecht embryological collections have been used to follow the structural development of the monotreme hypothalamus and its connections with the pituitary gland both in the period leading up to hatching and during the lactational phase of development, and to relate this structural maturation to behavioural development. In the incubation phase, development of the hypothalamus proceeds from closure of the anterior neuropore to formation of the lateral hypothalamic zone and putative medial forebrain bundle. Some medial zone hypothalamic nuclei are emerging at the time of hatching, but these are poorly differentiated and periventricular zone nuclei do not appear until the first week of post-hatching life. Differentiation of the pituitary is also incomplete at hatching, epithelial cords do not develop in the pars anterior until the first week, and the hypothalamo-neurohypophyseal tract does not appear until the second week of post-hatching life. In many respects, the structure of the hypothalamus and pituitary of the newly hatched monotreme is similar to that seen in newborn marsupials, suggesting that both groups rely solely on lateral hypothalamic zone nuclei for whatever homeostatic mechanisms they are capable of at birth/hatching.

The cellular composition of neurogenic periventricular zones in the adult zebrafish forebrain

A central goal of adult neurogenesis research is to characterize the cellular constituents of a neurogenic niche and to understand how these cells regulate the production of new neurons. Because the generation of adult-born neurons may be tightly coupled to their functional requirement, the organization and output of neurogenic niches may vary across different regions of the brain or between species. We have undertaken a comparative study of six (D, Vd, Vv, Dm, Dl, Ppa) periventricular zones (PVZs) harboring proliferative cells present in the adult forebrain of the zebrafish (Danio rerio), a species known to possess widespread neurogenesis throughout life. Using electron microscopy, we have documented for the first time the detailed cytoarchitecture of these zones, and propose a model of the cellular composition of pallial and subpallial PVZs, as well as a classification scheme for identifying morphologically distinct cell types. Immunolabeling of resin-embedded tissue confirmed the phenotype of three constitutively proliferating (bromodeoxyuridine [BrdU]+) cell populations, including a radial glial-like (type IIa) cell immunopositive for both S100β and glutamine synthetase (GS). Our data revealed rostrocaudal differences in the density of distinct proliferative populations, and cumulative labeling studies suggested that the cell cycle kinetics of these populations are not uniform between PVZs. Although the peak numbers of differentiated neurons were generated after ~2 weeks among most PVZs, niche-specific decline in the number of newborn neurons in some regions occurred after 4 weeks. Our data suggest that the cytoarchitecture of neurogenic niches and the tempo of neuronal production are regionally distinct in the adult zebrafish forebrain.

Spatiotemporal distribution of white matter lesions in relapsing–remitting and secondary progressive multiple sclerosis

Background: Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system. MS lesions show a typical distribution pattern and primarily affect the white matter (WM) in the periventricular zone and in the centrum semiovale. Objective: To track lesion development during disease progression, we compared the spatiotemporal distribution patterns of lesions in relapsing–remitting MS (RRMS) and secondary progressive MS (SPMS). Methods: We used T1 and T2 weighted MR images of 209 RRMS and 62 SPMS patients acquired on two different 1.5 Tesla MR scanners in two clinical centers followed up for 25 (± 1.7) months. Both cross-sectional and longitudinal differences in lesion distribution between RRMS and SPMS patients were analyzed with lesion probability maps (LPMs) and permutation-based inference. Results: MS lesions clustered around the lateral ventricles and in the centrum semiovale. Cross-sectionally, compared to RRMS patients, the SPMS patients showed a significantly higher regional probability of T1 hypointense lesions (p≤0.03) in the callosal body, the corticospinal tract, and other tracts adjacent to the lateral ventricles, but not of T2 lesions (peak probabilities were RRMS: T1 9%, T2 18%; SPMS: T1 21%, T2 27%). No longitudinal changes of regional T1 and T2 lesion volumes between baseline and follow-up scan were found. Conclusion: The results suggest a particular vulnerability to neurodegeneration during disease progression in a number of WM tracts.

Localization and characterization of kal 1.a and kal 1.b in the brain of adult zebrafish (Danio rerio)

The gene underlying the X-chromosome-linked Kallmann syndrome KAL-1 has been identified for several years, yet its role is still poorly understood. During previous research, the KAL.1 orthologs, kal 1.a and kal 1.b, were isolated in zebrafish. In the present study, in situ hybridization was used to localize and compare the expression of kal 1.a and kal 1.b in the adult zebrafish brain (Danio rerio). The kal 1.a and kal 1.b transcription products have a similar distribution, both being localized in the olfactory bulb, in the ventral and posterior zones of the telencephalic area, hypothalamus, thalamus nuclei, corpus cerebelli, and many other nuclei, such as the posterior tuberal, the periventricular gray zone of the optic tectum, the periglomerular nucleus, the entopeduncular nucleus, parvocellular preoptic nucleus, habenular nucleus suprachiasmatic nucleus, magnocellular preoptic nucleus, griseum centrale, periventricular nucleus of the posterior tuberculum and the lobus caudallis cerebelli. In addition, by double approach of in situ hybridization and immunolabeling, it was found that, in telencephalon, the two genes are expressed in neurons and oligodendrocytes but they are not astrocytes. Finally, by using a proliferation marker, BrdU, kal 1.a and kal 1.b transcripts were shown to be clearly detected in a region previously described as an area of adult neurogenesis, suggesting that they may be involved in the process. Overall, our data provide a consolidated map of expression of kal 1.a and kal 1.b and suggest a distinct function of these genes, especially neurogenesis, in an adult context.

Effect of DYRK1A activity inhibition on development of neuronal progenitors isolated from Ts65Dn mice

Overexpression of dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A (DYRK1A), encoded by a gene located in the Down syndrome (DS) critical region, is considered a major contributor to developmental abnormalities in DS. DYRK1A regulates numerous genes involved in neuronal commitment, differentiation, maturation, and apoptosis. Because alterations of neurogenesis could lead to impaired brain development and mental retardation in individuals with DS, pharmacological normalization of DYRK1A activity has been postulated as DS therapy. We tested the effect of harmine, a specific DYRK1A inhibitor, on the development of neuronal progenitor cells (NPCs) isolated from the periventricular zone of newborn mice with segmental trisomy 16 (Ts65Dn mice), a mouse model for DS that overexpresses Dyrk1A by 1.5-fold. Trisomy did not affect the ability of NPCs to expand in culture. Twenty-four hours after stimulation of migration and neuronal differentiation, NPCs showed increased expression of Dyrk1A, particularly in the trisomic cultures. After 7 days, NPCs developed into a heterogeneous population of differentiating neurons and astrocytes that expressed Dyrk1A in the nuclei. In comparison with disomic cells, NPCs with trisomy showed premature neuronal differentiation and enhanced γ-aminobutyric acid (GABA)-ergic differentiation, but astrocyte development was unchanged. Harmine prevented premature neuronal maturation of trisomic NPCs but not acceleration of GABA-ergic development. In control NPCs, harmine treatment caused altered neuronal development of NPCs, similar to that in trisomic NPCs with Dyrk1A overexpression. This study suggests that pharmacological normalization of DYRK1A activity may have a potential role in DS therapy.

Significance of the Dynamic Expression of Pax6 and Dlx2 in the Postnatal Periventricular Zone Cells

Significance of the Dynamic Expression of Pax6 and Dlx2 in the Postnatal Periventricular Zone Cells

Quantitative imaging of Cu, Fe, Mn and Zn in the L-DOPA-treated unilateral 6-hydroxydopamine Parkinson's disease mouse model by LA-ICP-MS

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) imaging was used to generate quanti- tative elemental images of brain sections of mice with unilateral 6-hydroxydopamine (6-OHDA) lesions. In previous studies, an external calibration and regional image analysis strategy was developed and applied to serial sections at the level of the midbrain (including the substantia nigra, SN) of one 6-OHDA mouse. In this work, this strategy was validated by measuring sections at the striatum level in 18 6-OHDA-lesioned mice. 12 of these animals were treated with 6 mg kg −1 L-DOPA (L-3,4- dihydroxyphenylalanine, LD). The first estimate of the variance of in situ metal concentrations between animals amounting to 24% for Fe, 18% for Cu, 19% for Zn and 13% for Mn (RSD) in the cortex are provided. Concentrations of Fe, Cu, Mn and Zn were approximately identical in LD treated animals and controls. However, significantly lower concentrations of Fe (−7%) in the ventral and of Cu (−7%) in the dorsal striatum of the lesioned compared to the healthy hemisphere of all animals were detected. In controls, but not in LD treated animals, higher Cu concentrations were detected in the periventricular zone. The ratios of ventricular to parenchymal Cu can be considered as a measure of Cu efflux. The side difference of these values was significantly reduced by LD. Similar responses to LD countervailing at the healthy and 6-OHDA-lesioned sides have been described for other parameters such as dopamine receptors and transporters.

Dynamic expression of the pro-dopaminergic transcription factors Pax6 and Dlx2 during postnatal olfactory bulb neurogenesis

Olfactory bulb (OB) neurogenesis generates neurons that use GABA or dopamine as their neurotransmitters throughout life. Regionalized stem cell populations in the periventricular zone (PVZ) of the lateral ventricles (LVs) have been shown to be at the basis of neuronal diversity in the system. For example dopaminergic neurons arise predominantly from neural stem cells (NSCs) residing in the dorsal PVZ and depend on the expression of the transcription factors Pax6 and Dlx2 for their specification. In addition, Dlx2 is required for neurogenesis in general. Using targeted in vivo electroporation combined with immuno-fluorescence imaging and microarray analysis, we provide here detailed spatial and temporal expression data with cellular resolution in this system. We find that all along the neurogenic process Pax6 expression remains restricted to the dorsal PVZ, whereas nearly all neuroblasts express Dlx2, including those of the dorsal lineage, which are switched on for Dlx2 when they enter the rostral migratory stream (RMS). These data allow to explain and precise the functions of these two genes in postnatal OB neurogenesis.

Defining POMC Neurons Using Transgenic Reagents: Impact of Transient Pomc Expression in Diverse Immature Neuronal Populations

Melanocortin signaling plays a central role in the regulation of phenotypes related to body weight and energy homeostasis. To specifically target and study the function of proopiomelanocortin (POMC) neurons, Pomc promoter elements have been utilized to generate reporter and Cre recombinase transgenic reagents. Across gestation, we find that Pomc is dynamically expressed in many sites in the developing mouse forebrain, midbrain, hindbrain, spinal cord, and retina. Although Pomc expression in most embryonic brain regions is transient, it is sufficient to direct Cre-mediated recombination of floxed alleles. We visualize the populations affected by this transgene by crossing Pomc-Cre mice to ROSA reporter strains and identify 62 sites of recombination throughout the adult brain, including several nuclei implicated in energy homeostasis regulation. To compare the relationship between acute Pomc promoter activity and Pomc-Cre-mediated recombination at the single cell level, we crossed Pomc-enhanced green fluorescent protein (eGFP) and Pomc-Cre;ROSA-tdTomato lines. We detect the highest concentration of Pomc-eGFP+ cells in the arcuate nucleus of the hypothalamus and dentate gyrus but also observe smaller populations of labeled cells in the nucleus of the solitary tract, periventricular zone of the third ventricle, and cerebellum. Consistent with the dynamic nature of Pomc expression in the embryo, the vast majority of neurons marked with the tdTomato reporter do not express eGFP in the adult. Thus, recombination in off-target sites could contribute to physiological phenotypes using Pomc-Cre transgenics. For example, we find that approximately 83% of the cells in the arcuate nucleus of the hypothalamus immunoreactive for leptin-induced phosphorylated signal transducer and activator of transcription 3 are marked with Pomc-Cre;ROSA-tdTomato; only 13% of these are eGFP+ POMC neurons.