Monthly Archives: April 2019

Hey all!

This is the finale on our journey with the Cerebratulus lacteus! I dove into some research about the milky ribbon worm’s embryo and came across the Developmental Biology Journal, with a piece entitled ” β-catenin is required for the establishment of vegetal embryonic fates in the Nemertean, Cerebratulus lacteus“. Well, that’s a mouthful– but what does this mean for our milky ribbon worm? Essentially, this journal piece goes in-depth on how the embryo of C. lacteus— specifically, how this protein has an effect on the formation of the mesendoderm layer of the embryo. The purpose overall was to figure out how beta-catenin affects embryo formation in the Cerebratulus lacteus and if there was any other determining factor in the organism affected by the protein. There are typically 3 germ layers of a triploblastic organism: the endoderm, which is the inner layer, the mesoderm, which is the middle layer, and the ectoderm, which is the outer layer. The mesendoderm is the layer of the embryo that becomes the mesoderm and the endoderm; it is common among some animal groupings, but not all. 

The writers of the paper provided keywords for readers to properly comprehend the information from the paper; the four terms were Lophotrochozoa. development, evolution, and signaling.  Lophotrochozoa refers to one of the two groupings of Protosomal organisms, mainly those that do not undergo molting, including the Cerebratulus lacteus. Development simply refers to a process of growth and may refer to multiple aspects of an organisms’ life. In the case of this paper, development is tied to the growth of an embryo into a completely formed milky ribbon worm. Evolution can be defined on a large scale as macroevolution, or on a small scale as microevolution. Microevolution refers to changes within a population of the gene frequencies, while macroevolution is the major changes affecting a species due to smaller scale evolutionary changes.  Signaling can be an indication that an event has taken place. 

The hypothesis for this experiment is that β-catenin plays an important role in the “gastrulation, the specification of the endoderm, and establishment of dorsoventral polarity in C. lacteus.” This is still quite a loaded statement, so let’s break it down: The researchers in this study believe that based on the history of the protein beta-catenin and its behavior on other organisms, it affects multiple aspects of the milky ribbon worm embryo formation.  Specifically, the protein is key for the folding of the vegetal plate to produce the mesoderm (which is gastrulation), then give the mesoderm its functions to make other components of the embryo, like the formation of the internal organs (specification), and the formation of poles in the embryo. The numbers labeled in the visual below display a fertilized blastocyst with the abembryonic pole at one and the embryonic pole at 2.

The image displays the poles of a fertilized embryo, as described above. 

http://www.embryology.ch/anglais/evorimplantation/furchung04.html

There were many preparations conducted in the methods of this experiment, but many related to the extraction and cloning of β-catenin protein to observe in C. lacteus embryos. Our main focus is on how this protein affects the milky ribbon worm embryo fate.  The methods that actually involved the Cerebtratulus lacteus included the ‘preparing’ of the embryos and maintaining them in specific conditions to prevent bacterial growth before testing and staining endodermal cells of the milky ribbon worm with the enzyme esterase to physically see nuclei inside of the larva. Following these procedures, some larva were injected with a fluorescent molecule called morpholinos to observe the behavior of the embryos with the β-catenin; those not injected were considered control larvae. It was found that the β-catenin was affecting all of the hypothesized aspects of embryo development, but it is not required. Compared to the normal formation, embryos injected with morpholinos developed odd shapes– additionally, the endoderm did not form, and there was not any gastrulation as seen from the staining results.

What do these results mean for the C. lacteus?  The milky ribbon worm is not necessarily positively impacted by the β-catenin on endodermal tissue, and the hypothesis was not supported. It was also concluded that due to the lack of gastrulation of the milky ribbon worm embryos, there was more of the ectodermal layer produced. Without the folding to produce the endoderm, there was an excessive amount of ectoderm tissue in the worms. Other than this, the embryos behaved normally– the only difference was the lack of a true endoderm layer. The main points of the paper worked to understand how the embryos behaved, in terms of if there was loss of function (when embryos did not behave like controls, lacks embryo layers, or lacked movement) or gain of function (in which there was over-expression leading to too much tissue or particularly odd behavior normal milky ribbon worms did not usually do).

These findings are new because the Cerebratulus lacteus is not well researched. This paper is the only experimental research studying various aspects of the milky ribbon worm embryo is relatively new information about the organism simply because not much is know about it. These findings also help us try to understand more about how animals develop, specifically how organisms in Phylum Nemertea develop into their final adult states. 

This visual shows the milky ribbon worm in its natural environment!

https://www.alamy.com/cerebratulus-lacteus-galicia-spain-image60961726.html

Journal Article information: https://www.sciencedirect.com/science/article/pii/S0012160608001681

Authors: Jonathan Q. Henry, Kimberly J. Parry, Jason Wever, Elaine Seaver, and Mark Q. Martindale

Journal and Page Numbers- Development Biology, Volume 317, Issue 1. Pages 368-379

Citations – 

https://www.cell.com/cell/fulltext/S0092-8674(01)00307-5

https://www2.gwu.edu/~darwin/BiSc151/Lopho/Lophotrochozoa.html

Nusnbaum, Matthew “2- Evolution, Speciation, and Phylogeny” Powerpoint.

https://embryo.asu.edu/pages/mesoderm

Hey Everyone, 

The broader phylogenetic relationship between the milky ribbon worm,  Cerebratulus lacteus, and other organisms in its genus are quite interesting. In fact, most phylogenetic trees with the milky ribbon worms are not closely grouped with other members in the Cerebratulus genus. I discovered two different phylogenies (seen below) both based on the cytochrome oxidase 1 mitochondrial DNA and 28S ribosomal RNA gene sequences, but the trees are not the exact same.

The above image displays a phylogenetic tree of organisms in the class Lineidae. The Cerebratulus lacteus is grouped next to the Micrura chlorapardalis. 

The above image shows a phylogenetic tree also of organisms in the family Lineidae, but the Cerebratulus lacteus is grouped separately. However, the Cerebratulus marginatus and Micrura rubramaculosa are grouped together and located very close to the milky ribbon worm. 

There are multiple species outside of the Cerebratulus genus on the tree, but all the organisms are still in the family Lineidae– specifically, more than 8 genera are represented on both phylogenies. Furthermore, the Cerebratulus lacteus and other organisms within the genus are commonly grouped very closely to organisms in the genus Micrura, which is extremely interesting; one would think that an animal would be more related to the fellow organisms in the genus. From there, the question is, what makes the organisms in Cerebratulus and Micrura similar?

The problem is, this question has not been answered. There has not been any adequate evidence pointing to why organisms in the genus Micrura and Cerebratulus are phylogenetically similar.

There is an ongoing issue concerning multiple aspects of phylogeny with organisms in the phylum Nemertea. Scientists are concerned about the groupings of this phylum because they were largely organized based on physical features like color, shape, and size by Heinrich Otto Wilhelm Bürger in the early 20th century. The issue is that these traits are considered ‘un-taxonomically reliable’, and they were grouped this way mainly because Bürger was unable to study internal features. As a result, many species were thrown into the four ‘known’ genera groups– Cerebratulus and Lineus are genera groups in class Anolopa, and Prostoma and Amphiporus are genera in the class Enolopa. Non-coincidentally, these groups are the most studied genera out of 29 genus groups in the order Heteronemertea, and this order was classified by large size and overall musculature (which is not necessarily the best method of classification). Scientists have been able to provide some literature and general information about the behavior, physiology, and many other aspects of these organisms lives. However, having some information is not enough to thoroughly study and distinguish these species. The single trait so far (since these organisms are still being studied) that separates the milky ribbon worm from other members of its genus is the toxin it produces in an attack.

Researchers have discovered that this is not only a species related problem; even ‘known’  genera were not well classified. In turn, scientists are not really sure what makes each group distinct. It was so serious that when originally trying to classify the Cerebratulus truncatus, the organism had notable characteristics of both the Cerebratulus genus and the Lineus genus, so it was termed as nomina duba. This basically meant that scientists did not know where to put the organism, so it remained ‘taxnomically inadequate.’ There are many other organisms that have the same issue with overlapping traits. From what is understood about these animals, there are not many characteristics that truly set them apart as unique.

I believe these trees are said to be derived from the same information but not completely because of this enormous classification issue. These animals are not well understood by lots of scientists, and many of them have tried to classify them to understand their distinguishable features, but there has not been anything definite with concrete evidence to support their theories. Perhaps the start of the solution to this problem would be a re-classification of this phylum.

Citations-

https://www.biodiversity.no/Pages/196711

https://core.ac.uk/download/pdf/39323074.pdf

https://www.researchgate.net/figure/Phylogenetic-tree-resulting-from-maximum-likelihood-analysis-of-combined-COI-18S-and_fig3_317021243

https://www.researchgate.net/figure/Phylogeny-resulting-from-a-maximum-likelihood-analysis-of-28S-ribosomal-RNA-likelihood_fig5_233225614

https://www.researchgate.net/publication/233225614_Redescription_of_Lineus_acutifrons_Southern_1913_Nemertea_Pilidiophora_and_comments_on_its_phylogenetic_position

https://academic.oup.com/icb/article/25/1/5/2031761

Ebook- Report on the scientific results of the H.M.S Challenger by John Murray, pages 37-39 (https://play.google.com/books/reader?id=bhscAQAAMAAJ&hl=en&pg=GBS.PP7)