Evo Devo

Evolutionary Developmental Biology (a.k.a Evo Devo) is a growing field of biology that stands at the interface between evolutionary biology and developmental biology. With an ever increasing knowledge base, the literature on the topic is becoming increasingly difficult to wade through. I hope this blog can highlight the important findings in the field that anyone, scientist or layperson, may find interesting and enjoyable.

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The Notch intracellular signaling pathway is unusual in its requirement of cell–cell contact for activity of the membrane bound Notch receptor and ligand as well as for its direct mechanism of signal transduction through endocytosis of a portion of the receptor without amplification through second-messenger cascades. Notch receptors are characterized by an extracellular domain containing both ligand recognition as well as negative control regions that mediate receptor cleavage and the subsequent activation of the pathway. Notch activation is triggered by binding of a DSL domain-bearing ligand, that like Notch, must be endocytosed for proper activity of the pathway. Once cleaved, the intracellular domain of Notch acts directly through conserved protein domains as a co-transcriptional activator with suppressor of hairless (Su(H)/RBPjK) on downstream targets. These targets include hairy and enhancer of split (Hes), and enhancer of split (E)spl as well as a growing number of reported potential targets, many of which are in themselves transcription factors. Notch, these downstream targets, and ligands of Notch form the “canonical Notch signaling pathway”.
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Cnidarians are an early branching basal metazoan group with a
relatively simple body plan. Anthozoan cnidarians such as Nematostella vectensis, the starlet sea aneomone, are diploblastic with only a single gut opening and two main body axes, the oral–aboral and directive axes. Despite their apparent morphological simplicity, cnidarians have been shown to have considerable genomic complexity and possess nearly complete repertoires of all major metazoan signaling pathways. This enigmatic contrast between molecular complexity and morphological readout has prompted a number of studies on the role of developmental signaling pathways in these ancient animals. Surprisingly, a number of parallels between Cnidarian and Bilaterian development have emerged.
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The presence of the Notch signaling pathway in basal metazoans such as N. vectensis is particularly fascinating considering its nearly universal requirement throughout Bilateria in mediating cell–cell communication in extremely varied developmental contexts. This requirement for local signaling to specify defined sub-populations of cells makes the Notch pathway a particularly important candidate for study in early cnidarian embryogenesis.
…
Notch mediates partitioning of the tentacle field in Nematostella and may indicate a conserved role for Notch signaling in the demarcation of morphological territories. Notch has a role in segment formation in both vertebrates and arthropods and has been recently shown to mediate bud separation in asexual budding of the cnidarian hydra. This indicates that in both cnidarians and bilaterians, and therefore what is inferred to be the case for the eumetazoan ancestor, partitioning of morphological territories was among the ancestral roles of the pathway.
Marlow et al. 2012. Developmental Biology.

The Notch intracellular signaling pathway is unusual in its requirement of cell–cell contact for activity of the membrane bound Notch receptor and ligand as well as for its direct mechanism of signal transduction through endocytosis of a portion of the receptor without amplification through second-messenger cascades. Notch receptors are characterized by an extracellular domain containing both ligand recognition as well as negative control regions that mediate receptor cleavage and the subsequent activation of the pathway. Notch activation is triggered by binding of a DSL domain-bearing ligand, that like Notch, must be endocytosed for proper activity of the pathway. Once cleaved, the intracellular domain of Notch acts directly through conserved protein domains as a co-transcriptional activator with suppressor of hairless (Su(H)/RBPjK) on downstream targets. These targets include hairy and enhancer of split (Hes), and enhancer of split (E)spl as well as a growing number of reported potential targets, many of which are in themselves transcription factors. Notch, these downstream targets, and ligands of Notch form the “canonical Notch signaling pathway”.

Cnidarians are an early branching basal metazoan group with a

relatively simple body plan. Anthozoan cnidarians such as Nematostella vectensis, the starlet sea aneomone, are diploblastic with only a single gut opening and two main body axes, the oral–aboral and directive axes. Despite their apparent morphological simplicity, cnidarians have been shown to have considerable genomic complexity and possess nearly complete repertoires of all major metazoan signaling pathways. This enigmatic contrast between molecular complexity and morphological readout has prompted a number of studies on the role of developmental signaling pathways in these ancient animals. Surprisingly, a number of parallels between Cnidarian and Bilaterian development have emerged.

The presence of the Notch signaling pathway in basal metazoans such as N. vectensis is particularly fascinating considering its nearly universal requirement throughout Bilateria in mediating cell–cell communication in extremely varied developmental contexts. This requirement for local signaling to specify defined sub-populations of cells makes the Notch pathway a particularly important candidate for study in early cnidarian embryogenesis.

Notch mediates partitioning of the tentacle field in Nematostella and may indicate a conserved role for Notch signaling in the demarcation of morphological territories. Notch has a role in segment formation in both vertebrates and arthropods and has been recently shown to mediate bud separation in asexual budding of the cnidarian hydra. This indicates that in both cnidarians and bilaterians, and therefore what is inferred to be the case for the eumetazoan ancestor, partitioning of morphological territories was among the ancestral roles of the pathway.

Marlow et al. 2012. Developmental Biology.

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