Cnidarians Developmental Biology and Molecular Ecology

Head of the Lab: Dr. Tamar Lotan


עבור לגרסה העברית


Cnidaria is one of the most ancient multicellular phyla, having evolved 700 million ago. The phylum, which includes organisms such as jellyfish, sea anemones, corals and hydra, is considered a sister group to the Bilateria. Cnidarians are commonly characterized by a single body axis, only two germ layers, namely ectoderm and endoderm, and unique highly complex stinging capsules. In addition to their morphological simplicity, cnidarians have a high level of developmental plasticity that equips them for shape transformation, regeneration and asexual proliferation during their life cycle. Cnidarians are also key players in the marine ecosystem, acting as reef structure builders and as both predators and prey.

These unique characteristics, together with their basal position in the evolutionary tree, make the cnidarians an important group for studies of basic developmental and evolutionary processes, as well as of environmental adaptations. We are interested in understanding cnidarian developmental biology and molecular ecology as detailed below.

Development Programming

Cnidarians have a well-defined embryogenesis program, but are also capable of propagating using asexual reproduction via fission, budding or strobilation. The ability of cnidarians to undergo multiple developmental programs can have profound ecological and evolutionary consequences.   Our goal is to understand the critical decision junctions that give rise to development programming during cnidarians life cycle via sexual or asexual mode of reproduction.To explore these stages we are using the sea anemone Nematostella vectensis and the jellyfish Aurelia aurita.

Oogenesis: We are interested in understanding the oogenesis processes from the very early determination of the primordial germ cells (PGCs) through oocyte maturation to early stages of embryogenesis. Identifying the molecular pathways that govern the differentiation of PGCs into germline stem cells is a key to deciphering the genetic program that carries the potential to form new life. However, little is known about the mechanisms that execute this program in Cnidaria. We take advantage of the emerging genetic model of the sea anemone Nematostella vectensis, as its full genomic sequence has been published, molecular tools are available and its reproduction can be controlled and induced in the lab.

In order to get an initial insight into the oogenesis process, we have analyzed five different stages from early oogenesis to first embryonic divisions using a proteomic approach. We compared the proteomic profiles of mature ovulated oocyte of Nematostella to MII oocyte stage of mouse, two organisms that diverged 500 million years ago. Our findings suggest that oocyte proteome template predates the divergence of the cnidarian and bilaterian lineages. This was the first proteomic oocyte study done in Cnidaria. Currently, we are testing selected pathways by analyzing proteins expression and function. To detect PGC differentiation, we are creating transgenic animals using promoters of known stem cells, such as vasa and nanos, linked to fluorescent markers.




Jellyfish strobilation:  In the class Scyphozoa, where the medusa phase is the dominant part of the life cycle, the polyp’s asexual proliferation results in the production of dozens of juvenile medusas (ephyra) in a repeated segmented process called strobilation. This rapid proliferation leads to jellyfish outbreaks around the globe, which in the last decade seem to have become more severe and frequent. To study the strobilation process, we use the moon jellyfish Aurelia aurita as a model system.  We have generated a wide data set using next-generation sequencing of six developmental stages in order to study strobila and ephyra development. Elucidating the mechanistic processes that give rise to medusa development is essential to our understanding of both jellyfish evolution and proliferation.

Cnidarian stinging capsules 

The Cnidarians' stinging cells manufacture intracellular structures known as cnidocysts, cyst capsules, loaded with an array of toxins. Upon activation of the capsule, a high internal pressure of 150 bars develops, resulting in the discharge of a folded tubule at an acceleration of 5 x106 g immediately releasing the toxin arsenal into the target cell. About 30 subtypes of capsules are known, all functioning on the same principles, but differing in size, shape and length of the tubule. How is the rigid capsule assembled within the stinging cell? What are the biological active compounds which are delivered into the prey? Can we gain insight into the constraints that shape the capsule?  

To answer these questions, we have adopted a multidisciplinary approach that combines biology, fish parasitology, micro- and nano-fluidics and drug delivery. We study a group of parasites known as Myxozoa, which was recently placed within the Cnidaria phylum, in order to decipher stinging cell evolution, development and function. This basic research has important application as these parasites have devastating effects on aquaculture and natural fish populations. To test the physical characteristics and the internal osmotic pressures of the stinging capsules, we utilize fabricated chips with high-speed camera. To uncover the contents of the stinging capsules, we apply proteomics combined with transcriptomics. Combining molecular data with the physical approach accelerates our understanding of the evolution and function of the stinging capsules.  











The Impact of Marine Pollution

Heavy metal contamination poses a global threat to the marine environment, as heavy metals are passed up the food chain and persist in the environment long after the pollution source is contained. We employed a transcriptome-wide RNA-Seq approach to analyze Nematostella molecular defense mechanisms against four heavy metals. We identified, co-upregulation of immediate-early transcription factors such as Egr1 and AP1. These immediate-early transcription factors may play a role in the first line of protection against the polluted environment. In addition, we revealed a new pathway of defense that regulates the synthesis of the metal-binding phytochelatins, instead of the metallothioneins that are absent from the Cnidaria genome. Currently, we are using phosphorylation assays to understand the role of MAPKs in the processes. Our ultimate goal is to understand how the polluted environment is perceived within the cells to increase anemone adaptation. 

Bloom of Jelly Fish     The Impact of Marine Pollution




ביולוגיה התפתחותית ואקולוגיה מולקולרית של צורבים

מערכת הצורבים כוללת את שושנות הים, האלמוגים, ההידרות, המדוזות ויש לה תפקיד חשוב במערך האקולוגי הימי. בנוסף לחקר הצורבים יש השלכות אקולוגיות, אבולוציוניות, רפואיות וכלכליות. בעשור באחרון, יחד עם התפתחות הכלים המולקולרים והריצוף הגנומי צורפה למערכה של הצורבים קבוצה גדולה של טפילים בשם מיקסוזואה, המציגה את המערכה באור חדש ונותנת לנו הצצה לתהליכי התפתחות של מנגנוני הצריבה היחודיים למערכה.

תחומי המחקר העיקריים במעבדה כוללים:

  • חקר תהליכי התפתחות של מינים כמו מדוזה ושושנת ים שהופיעו לראשונה בשחר האבולוציה, לפני קרוב ל-700 מיליון שנה, והשוואתם עם תהליכי התפתחות בבע"ח מפותחים יותר. המעבדה מתמקדת בשאלות כמו: האם תהליכי הבקרה בהתפתחות הביצית בצורבים משותפים גם להתפתחות הביצית ביונקים? כיצד מתרחש תהליך המטמורפוזה מפגית (לרווה) השוחה בים לפוליפ הצמוד למצע ? או כיצד מפוליפ אחד נוצרות עשרות מדוזות?
  • חקר מסלולים ביוכימיים ובקרתם הגנטית בתהליך קביעת תאי המין מתאי גזע במטרה לקדם הבנה בסיסית של שלבים ראשוניים בהיווצרות בע"ח.
  • המעבדה מפתחת אמצעי ניטור של זיהומים כמו מתכות כבדות, המבוססים על הבנת מנגנון ההגנה של צורבים.
  • מחקר של מערכות הזרקה טבעיות בגודל מיקרוסקופי. למנגנון הצריבה של הצורבים יכולת הזרקת נוזלים בלחץ של 150 אטמוספרות בחלקיקי שנייה. במעבדה מתבצע מחקר ביולוגי והנדסי להבנת תהליכי בנית המזרק ויצירת הלחץ במערכת, לצד הבנת הזרימה דרך צינור (מחט) בקוטר ננומטרי.
  • הבנת מנגנוני ההזרקה בקבוצת המיקסוזואה המנצלת מנגנונים אלו למטרות שונות ויחודיות לקבוצה.

למעבדה גישה לים התיכון לצד יכולת גידול של שלבי החיים השונים של המדוזות ושושנות הים. המחקר מתמקד בשאלות הנ"ל מרמת בעה"ח השלם דרך המערכת התאית ועד לרמה המולקולרית של ה- RNA והחלבון.

השריית מצב של יצירת ריבוי זרועות ציד בכל גוף השושנה- ע"י שינוי בקרת הגנים


מנגנוני הצריבה בצורבים


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