Browsing by Author "Martindale, Mark Q"

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    Developmental and light-entrained expression of melatonin and its relationship to the circadian clock in the sea anemone Nematostella vectensis
    (2014-08-14) Peres, Rafael; Reitzel, Adam M; Passamaneck, Yale; Afeche, Solange C; Cipolla-Neto, José; Marques, Antonio C; Martindale, Mark Q
    Abstract Background The primary hormone of the vertebrate pineal gland, melatonin, has been identified broadly throughout the eukaryotes. While the role for melatonin in cyclic behavior via interactions with the circadian clock has only been reported in vertebrates, comparative research has shown that the transcription-translation loops of the animal circadian clock likely date to the cnidarian-bilaterian ancestor, leaving open significant questions about the evolutionary origin of melatonin signaling in circadian behavior by interacting with the molecular clock. Results Expression of melatonin in adult anemones showed peak expression at the end of light period (zeitgeber time (ZT)and#8201;=and#8201;12) when cultured under diel conditions, coinciding with expression of genes and enzyme activity for members of the melatonin synthesis pathway (tryptophan hydroxylase and hydroxyindol-O-methyltransferase), which also showed rhythmic expression. During embryogenesis and juvenile stages, melatonin showed cyclic oscillations in concentration, peaking in midday. Spatial (in situ hybridization) and quantitative (real-time PCR) transcription of clock genes during development of N. vectensis showed these and#8216;clockand#8217; genes are expressed early in the development, prior to rhythmic oscillations, suggesting functions independent of a function in the circadian clock. Finally, time-course studies revealed that animals transferred from diel conditions to constant darkness lose circadian expression for most of the clock genes within 4and#160;days, which can be reset by melatonin supplementation. Conclusions Our results support an ancient role for melatonin in the circadian behavior of animals by showing cyclic expression of this hormone under diel conditions, light-dependent oscillations in genes in the melatonin synthesis pathway, and the function of melatonin in initiating expression of circadian clock genes in the cnidarian N. vectensis. The differences in expression melatonin and the circadian clock gene network in the adult stage when compared with developmental stages of N. vectensis suggests new research directions to characterize stage-specific mechanisms of circadian clock function in animals.
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    Expression of multiple Sox genes through embryonic development in the ctenophore Mnemiopsis leidyi is spatially restricted to zones of cell proliferation
    (2014-04-24) Schnitzler, Christine E; Simmons, David K; Pang, Kevin; Martindale, Mark Q; Baxevanis, Andreas D
    Abstract Background The Sox genes, a family of transcription factors characterized by the presence of a high mobility group (HMG) box domain, are among the central groups of developmental regulators in the animal kingdom. They are indispensable in progenitor cell fate determination, and various Sox family members are involved in managing the critical balance between stem cells and differentiating cells. There are 20 mammalian Sox genes that are divided into five major groups (B, C, D, E, and F). True Sox genes have been identified in all animal lineages but not outside Metazoa, indicating that this gene family arose at the origin of the animals. Whole-genome sequencing of the lobate ctenophore Mnemiopsis leidyi allowed us to examine the full complement and expression of the Sox gene family in this early-branching animal lineage. Results Our phylogenetic analyses of the Sox gene family were generally in agreement with previous studies and placed five of the six Mnemiopsis Sox genes into one of the major Sox groups: SoxB (MleSox1), SoxC (MleSox2), SoxE (MleSox3, MleSox4), and SoxF (MleSox5), with one unclassified gene (MleSox6). We investigated the expression of five out of six Mnemiopsis Sox genes during early development. Expression patterns determined through in situ hybridization generally revealed spatially restricted Sox expression patterns in somatic cells within zones of cell proliferation, as determined by EdU staining. These zones were located in the apical sense organ, upper tentacle bulbs, and developing comb rows in Mnemiopsis, and coincide with similar zones identified in the cydippid ctenophore Pleurobrachia. Conclusions Our results are consistent with the established role of multiple Sox genes in the maintenance of stem cell pools. Both similarities and differences in juvenile cydippid stage expression patterns between Mnemiopsis Sox genes and their orthologs from Pleurobrachia highlight the importance of using multiple species to characterize the evolution of development within a given phylum. In light of recent phylogenetic evidence that Ctenophora is the earliest-branching animal lineage, our results are consistent with the hypothesis that the ancient primary function of Sox family genes was to regulate the maintenance of stem cells and function in cell fate determination.
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    Non-canonical Notch signaling represents an ancestral mechanism to regulate neural differentiation
    (2014-09-19) Layden, Michael J; Martindale, Mark Q
    Abstract Background Cellular differentiation is a critical process during development of multicellular animals that must be tightly controlled in order to avoid precocious differentiation or failed generation of differentiated cell types. Research in flies, vertebrates, and nematodes has led to the identification of a conserved role for Notch signaling as a mechanism to regulate cellular differentiation regardless of tissue/cell type. Notch signaling can occur through a canonical pathway that results in the activation of hes gene expression by a complex consisting of the Notch intracellular domain, SuH, and the Mastermind co-activator. Alternatively, Notch signaling can occur via a non-canonical mechanism that does not require SuH or activation of hes gene expression. Regardless of which mechanism is being used, high Notch activity generally inhibits further differentiation, while low Notch activity promotes differentiation. Flies, vertebrates, and nematodes are all bilaterians, and it is therefore unclear if Notch regulation of differentiation is a bilaterian innovation, or if it represents a more ancient mechanism in animals. Results To reconstruct the ancestral function of Notch signaling we investigate Notch function in a non-bilaterian animal, the sea anemone Nematostella vectensis (Cnidaria). Morpholino or pharmacological knockdown of Nvnotch causes increased expression of the neural differentiation gene NvashA. Conversely, overactivation of Notch activity resulting from overexpression of the Nvnotch intracellular domain or by overexpression of the Notch ligand Nvdelta suppresses NvashA. We also knocked down or overactivated components of the canonical Notch signaling pathway. We disrupted NvsuH with morpholino or by overexpressing a dominant negative NvsuH construct. We saw no change in expression levels for Nvhes genes or NvashA. Overexpression of Nvhes genes did not alter NvashA expression levels. Lastly, we tested additional markers associated with neuronal differentiation and observed that non-canonical Notch signaling broadly suppresses neural differentiation in Nematostella. Conclusions We conclude that one ancestral role for Notch in metazoans was to regulate neural differentiation. Remarkably, we found no evidence for a functional canonical Notch pathway during Nematostella embryogenesis, suggesting that the non-canonical hes-independent Notch signaling mechanism may represent an ancestral Notch signaling pathway.