The neural stem cell lineage reveals novel relationships among spermatogonial germ stem cells and other pluripotent stem cells.

The embryonic stem cell (ESC) derived from the inner cell mass is viewed as the core pluripotent cell (PC) type from which all other cell types emanate. This familiar perspective derives from an embryological time line in which PCs are ordered according to their time of appearance. However, this schema does not take into account their potential for interconversion, thereby excluding this critical quality of PCs. The persistence of bona fide pluripotent adult stem cells has garnered increasing attention in recent years. Adult pluripotent spermatogonial germ stem cells (aSGSCs) arise from primordial germ cells (pGCs) that emerge from the epiblast during gastrulation. Adult definitive neural stem cells (dNSCs) arise clonally from pluripotent embryonic primitive neural stem cells (pNSCs), which can also be derived clonally from ESCs. To test for stem cell-type convertibility, we employed differentiation in the clonal lineage from ESCs to pNSCs to dNSCs, and revealed the relationships and lineage positioning among various PC populations, including spermatogonial germ cells (aSGSCs), epiblast-derived stem cells (Epi-SCs) and the bFGF, Activin, and BIO-derived stem cell (FAB-SC). Adult, murine aSGSCs assumed a 'pseudo-ESC' state in vitro, and then differentiated into dNSCs, but not pNSCs. Similarly, Epi-SCs and FAB-SCs only gave rise to dNSCs and not to pNSCs. The results of these experiments suggest a new pluripotency lineage model describing the relationship(s) among PCs that better reflects the transitions between these cell types in vitro.

Entwined engrams: The evolution of associative and non-associative learning.

The nematode Caenorhabditis elegans displays a surprisingly sophisticated behavioral repertoire that includes the utilization of both associative and non-associative forms of learning. Elucidating the molecular basis of learning remains a fundamental, yet daunting, challenge of modern neuroscience. In Pereira and van der Kooy (ref. 2), we described the use of a two input-two output stimuli system to dissociate between associative and non-associative learning and between memory acquisition and retrieval processes. Briefly, one finding indicated that after training with the odorant isoamyl alcohol (IsoA), we could preferentially retrieve either associative or non-associative memory with a choice of either a benzaldehyde (Bnz) or IsoA retrieval stimulus, respectively. Here, we describe how that apparently enigmatic molecular cross wiring of the two forms of memory examined could represent an evolutionary relic of the ancient divergence between non-associative and associative learning. In addition, we extrapolate on the utility and subtleties of using such a system to dissociate and decipher the components of memory in C. elegans.

Ontogeny of human umbilical cord perivascular cells: molecular and fate potential changes during gestation.

Human umbilical cord-derived perivascular cells (PVCs) are a recently characterized source of mesenchymal stromal cells that has gained much interest in the field of cellular therapeutics. However, very little is known about the changes in fate potential and restrictions that these cells undergo during gestational development. This study is the first to examine the phenotypic, molecular, and functional properties of first trimester (FTM)-derived PVCs, outlining properties that are unique to this population when compared to term (TERM) counterparts. FTM- and TERM-PVCs displayed analogous mesenchymal, perivascular, and immunological immunophenotypes. Both PVCs could be maintained in culture without alteration to these phenotypes or mesenchymal lineage differentiation potential. Some unique features of FTM-PVCs were uncovered in this study: (1) while the gene signatures of FTM- and TERM-PVCs were similar, key differences were observed, namely, that the Oct4A and Sox17 proteins were detected in FTM-PVCs, but not in TERM counterparts; (2) FTM-PVCs exhibited a greater proliferative potential; and (3) FTM-PVCs were more efficient in their in vitro differentiation toward selective mesenchymal cell types, including the chondrogenic and adipogenic lineages, as well as toward neuronal- and hepatocyte-like lineages, when compared to TERM-PVCs. Both PVCs were able to generate osteocytes and cardiomyocyte-like cells with similar efficiencies in vitro. Overall, FTM-PVCs show more plasticity than TERM-PVCs with regard to fate acquisition, suggesting that a restriction in multipotentiality is imposed on PVCs as gestation progresses. Taken together, our findings support the idea that PVCs from earlier in gestation may be better than later sources of multipotent stromal cells (MSCs) for some regenerative medicine applications.

Nicotine-motivated behavior in Caenorhabditis elegans requires the nicotinic acetylcholine receptor subunits acr-5 and acr-15.

Signaling at nicotinic acetylcholine receptors in Caenorhabditis elegans controls many behaviors, including egg-laying and locomotor activity. Here, we show that C. elegans approaches a point source of nicotine in a time-, concentration- and age-dependent manner. Additionally, nicotine paired with butanone under starvation conditions prevented the reduced approach to butanone that is observed when butanone is paired with starvation alone and pairing with nicotine generates a preference for the tastes of either sodium or chloride over baseline. These results suggest nicotine acts as a rewarding substance in C. elegans. Furthermore, the nicotinic receptor antagonist mecamylamine, the smoking cessation pharmacotherapy varenicline, mutation of the dop-1 and dop-2 dopamine receptors, and mutations of either acr-5 or acr-15, two nicotinic receptor subunit genes with sequence homology to the mammalian α7 subunit, all reduced the nicotine approach behavior. These two mutants also were defective at associating the presence of nicotine with butanone under starvation conditions and acr-5 mutation could obviate the effect of pairing nicotine with salts. Furthermore, the approach deficit in acr-15 mutants was rescued by selective re-expression in a subset of neurons, but not in muscle. Caenorhabditis elegans may therefore serve as a useful model organism for nicotine-motivated behaviors that could aid in the identification of novel nicotine motivational molecular pathways and consequently the development of novel cessation aids.

Two forms of learning following training to a single odorant in Caenorhabditis elegans AWC neurons.

The nematode Caenorhabditis elegans can adapt to both the AWC-sensed odorants benzaldehyde (Bnz) and isoamyl alcohol (IsoA) and can reciprocally cross-adapt. Yet we reveal that these four adaptation scenarios actually represent two distinct forms of learning: nonassociative habituation and associative learning by pairing with a starvation unconditioned stimulus. Training to the single odorant IsoA leads to both associative and nonassociative memory traces, which can be preferentially accessed by either a Bnz or IsoA retrieval stimulus, respectively. This represents the first demonstration in which the form of learning displayed after training to a single stimulus is a function of the retrieval stimulus used. Furthermore, these two forms of learning can be genetically double dissociated despite both forms occurring within the AWC primary sensory neuron. We find that associative learning requires the cGMP-dependent kinase egl-4 and insulin signaling, which acts downstream of egl-4. In contrast, nonassociative learning requires neither of these genes, but does require the TRPV channel osm-9, which is dispensable for associative learning. In addition, we find that the arrestin arr-1 is promiscuous between associative and nonassociative learning in mediating the adaptive response to the IsoA retrieval stimulus, suggesting that distinct forms of memory may nonetheless use common downstream effectors.

Insulin signaling plays a dual role in Caenorhabditis elegans memory acquisition and memory retrieval.

Insulin signaling plays a prominent role in regulation of dauer formation and longevity in Caenorhabditis elegans. Here, we show that insulin signaling also is required in benzaldehyde-starvation associative plasticity, in which worms pre-exposed to the odor attractant benzaldehyde in the absence of food subsequently demonstrate a conditioned aversion response toward the odorant. Animals with mutations in insulin-related 1 (ins-1), abnormal dauer formation 2 (daf-2), and aging alteration 1 (age-1), which encode the homolog of human insulin, insulin/IGF-1 receptor, and PIP3 kinase, respectively, demonstrated significant deficits in benzaldehyde-starvation associative plasticity. Using a conditional allele, we show that the behavioral roles of DAF-2 signaling in associative plasticity can be dissociated, with DAF-2 signaling playing a more significant role in the memory retrieval than in memory acquisition. We propose DAF-2 signaling acts as a learning-specific starvation signal in the memory acquisition phase of benzaldehyde-starvation associative plasticity but functions to switch benzaldehyde-sensing amphid wing C neurons into an avoidance signaling mode during memory retrieval.