Hydrozoan insights in animal development and evolution

Abstract

The fresh water polyp Hydra provides textbook experimental demonstration of positional information gradients and regeneration processes. Developmental biologists are thus familiar with Hydra, but may not appreciate that it is a relatively simple member of the Hydrozoa, a group of mostly marine cnidarians with complex and diverse life cycles, exhibiting extensive phenotypic plasticity and regenerative capabilities. Hydrozoan species offer extensive opportunities to address many developmental mechanisms relevant across the animal kingdom. Here we review recent work from non-Hydra hydrozoans - hydromedusae, hydroids and siphonophores - shedding light on mechanisms of oogenesis, embryonic patterning, allorecognition, stem cell regulation and regeneration. We also highlight potential research directions in which hydrozoan diversity can illuminate the evolution of developmental processes at micro- and macro-evolutionary time scales.

Diversity of Cnidarian Muscles: Function, Anatomy, Development and Regeneration

“…A handful of cnidarians has emerged in the past decades as experimental models in molecular, cell and developmental biology, providing insights into the evolution of developmental programs, including regeneration, stem cell biology and the evolution of key bilaterian traits (Kraus et al, 2007, 2016; Momose and Houliston, 2007; Amiel et al, 2009; Chera et al, 2009; Boehm et al, 2012; Layden et al, 2012; Röttinger et al, 2012; Sinigaglia et al, 2013; Leclère and Rentzsch, 2014; Abrams et al, 2015; Bradshaw et al, 2015; Helm et al, 2015; reviewed in Technau and Steele, 2011; Layden et al, 2016; Leclère et al, 2016; Rentzsch and Technau, 2016). The main, but not exclusive, cnidarian models are the medusozoan hydrozoans Hydra, Hydractinia, Podocoryna and Clytia (reviewed in Houliston et al, 2010; Galliot, 2012; Plickert et al, 2012; Gahan et al, 2016; Leclère et al, 2016) as well as the anthozoans Nematostella vectensis (reviewed in Layden et al, 2016; Rentzsch and Technau, 2016) and the coral Acropora (Shinzato et al, 2011; Hayward et al, 2015; Okubo et al, 2016).…”

“…The main, but not exclusive, cnidarian models are the medusozoan hydrozoans Hydra, Hydractinia, Podocoryna and Clytia (reviewed in Houliston et al, 2010; Galliot, 2012; Plickert et al, 2012; Gahan et al, 2016; Leclère et al, 2016) as well as the anthozoans Nematostella vectensis (reviewed in Layden et al, 2016; Rentzsch and Technau, 2016) and the coral Acropora (Shinzato et al, 2011; Hayward et al, 2015; Okubo et al, 2016). …”

A gonad-expressed opsin mediates light-induced spawning in the jellyfishClytia

“…Members of Hydrozoa, a subgroup of Cnidaria which can have medusae or polyps as the sexual form, commonly display light-regulated sexual reproduction. (Leclère et al, 2016;Siebert and Juliano, 2016). They have simple gonads in which the germ cells are sandwiched between ectoderm and endoderm, and unlike many other animals they lack additional layers of somatic follicle cells surrounding oocytes in the female (Deguchi et al, 2011).…”

The genome of the jellyfish Clytia hemisphaerica and the evolution of the cnidarian life-cycle

“…There are four classes of Medusozoa: the Cubozoa (box jellyfish), Scyphozoa (so-called 'true' jellyfish), Staurozoa (stalked 'jellyfish') and Hydrozoa [2,6]. Life cycles in different medusozoan lineages have undergone frequent modifications, including loss of polyp, planula and medusa stages.…”

“…1). Clytia is easy to maintain and manipulate, and amenable to gene function analysis including Cas9 mediated mutation, allowing mechanistic insight into cellular and developmental processes [6,11,12]. We analyse transcriptomes from all life cycle forms, illuminating the evolution of the planula, polyp and medusa, and demonstrate how the gene complement of the cnidarian-bilaterian ancestor provided the foundation of anatomical complexity in the medusa.…”