Reticulomyxa
Reticulomyxa Filosa
Reticulomyxa Filosa is a species in the group of single-celled foraminifera and the only representative of its genus from the order of Allogromiida. The 1949 first-described species is one of the few species of foraminifera that does not live in the sea, but in fresh water. In addition, it has, unlike the majority of foraminifera also no housing.
The type served since its rediscovery in the early 1980s as a model organism for cell biological research, since the turn of the millennium also for molecular genetic analyzes of systematic purposes. Through the work in this frame work, the species is unusually well researched for a single-celled. Features showed in particular with regard to the unusual manner of propagation, the formation of two different resting stages and the very powerful ways of transport of organelles within the cell.
- 2.1 nutrition
- 2.2 Reproduction
Features
The cells are surrounded by a slime sheath, almost immovable multinucleate plasmodia without housing or proteinaceous shell variable, net-like shape. Their diameter is usually around 1 to 3 centimeters, they can have a maximum dimension of up to 12 ( according to other sources up to 25 ) reach square centimeters. The organism can be divided into two areas, a central region and a peripheral region. The latter is formed by the radially outgoing from up to 6 mm in diameter measured central region of long, thread-like Retikulopodien. These are along with each other multiply linked ( anastomosis ) main strands thick on average by 100 (40 to 250) microns, but are tapered with fine foothills down to 1 micron thickness. Overall, they can reach a length of ten times the diameter of the central region.
The cytoplasm is coarse to fine-grained and white to pale pink. During the vegetative phase, it contains a lot of non- contractile vacuoles, a differentiation into endo-and ectoplasm is missing.
Ultrastructure
The cell comprises in the central area several thousand nuclei with a diameter of 5 to 6 microns, and with strong Diktyosome tank stacks.
The cytoskeleton consists almost entirely of microtubules, the content of actin is low. A centrosome is missing as well as a Mikrotubulusorganisationszentrum in the conventional sense, the latter is instead of a collar at the far end of the microtubules. Microtubules serve as rails for driving a bi-directional grain flow, which, in its periphery but leads away in the middle of pseudopodia from the central portion to him. The organelles thereby slidably move on the microtubules. The assembly and disassembly of microtubules in Reticulomyxa happens with remarkably high speed, build the Retikulopodien stretching speeds of up to 6.5 microns / second were measured in the degradation rates of up to 19.5 microns / second. It is unusual in that for the transport of organelles in both directions, a single microtubule is already sufficient, probably because the motor protein dynein included can operate in both directions.
Resting stage and cyst
Reticulomyxa Filosa has two different stages of quiescence, only one of which enveloped and therefore is but a cyst in the strict sense. Why the type forms two different types of resting stages is not known. Possible causes of seasonal processes or different functions are (possibly represents the non-enveloped resting stage is a propagation stage ).
Not Shrouded resting stage
This resting stage, which is caused by lack of food, extreme nutrient excess or cold, is created by the plasmodia to contract and then fragment. The resulting cells have a diameter of 50 to 100 micrometers. Except oversized Exozytosevesikeln and lack of microtubules - instead, however, numerous aggregated to Para crystals helical filaments -, the cells no different from active cells. A metabolism is still available.
A transition from the resting stage in the cyst form is not possible. But already a few minutes after normal conditions prevail, the resting stages are active again and begin to build a new retikulopodialen network.
Cyst
The true cyst forms as a result of lack of food. The Plasmodie contracts into a sausage shape and then disintegrates into several oval to spherical plasma sections. The cell image is associated with the beginning almost unchanged, only microtubules and helical filaments are largely absent completely. Over the next two days then starts the actual encystment. On the cell surface, many tube - to club-shaped appendages that are 20-40 nanometers thick and about 50 nanometers long, they are probably involved in the formation of the shell form. The envelope is in this phase, around 100 nanometers thick and consists of fine fibrils.
After three days, the shell has a thickness of 400 nanometers. In parallel, the degradation of many organelles, the plasma has begun, even the number of nuclei is reduced. Also, the previously existing rough endoplasmic reticulum is now missing. As a result of the degradation dark to disordered moving residual bodies are formed.
After about ten days, the encystment is completed. Which emerged from the mother cell cysts are now 50 to 200 microns in size, spherical or oval to bean-shaped and are often close to each other. They are surrounded by a 20 to 30 microns thick, gelatinous layer. The cyst wall is 1-2 micrometers thick and is reinforced from the inside by a layer of 50 nm thick fibrils on. To the rest of the body to the granules have aggregated. In the approximately 500 existing 3.5 micron nuclei nucleoli, neither microtubules nor tubulin Para crystals are locate missing. The cysts are now protected from dehydration and temperatures of up to -16 ° C. They remain viable for months. Only when rule over several days, good conditions, the cysts re-enable it. They solve by enzymes, the cyst shell at a point on, leave it and form again Retikulopodien.
Way of life
Reticulomyxa Filosa growing aquatic to semi -aquatic in the detritus of fresh water. The central areas are preferably in probably obscured by substrate or plant small niches or cavities from which protrude only the tips of Retikulopodien.
Nutrition
Reticulomyxa Filosa are omnivores, besides coming from the detritus nutrient particles they also feed on smaller unicellular and multicellular living organisms such as cyanobacteria, bacteria, rotifers, green algae and rarely ciliate. Although the processes are not documented in more details, but presumably the corresponding particles are taken up by the tips of the Retikulopodien be placed over the particles or by more of the Retikulopodien flow around the object in question, to unite with each other and so include the food. In multi-cellular or cell- colonial prey individual cells from the body are released. After this the phagocytosis vacuoles are transported into the central area using the granules flow. Already the road begins the digestion, but only completed in the central area, where the nutrients are then available. Incidental feces are excreted by the surfaces of the main routes where they provide a solid protective layer.
Reproduction
Sexual processes of Reticulomyxa Filosa are not known, documented is just a multiplication by division of the cell. Cell division occurs here in a unique way.
During growth of the organism, in particular of the central region, continuously, new nuclei. The increase in the cytoplasm and nuclei correlated. The nuclear divisions within the cell are synchronized according to previous observations, carried out within a few minutes, but not at regular intervals. Unlike most of protists, the nuclear envelope during the division is substantially maintained and is permeable only to the spindle microtubules. The nuclear envelope deposited nucleoli are not resolved, but given the resulting daughter nuclei.
If the cell has exhausted the resources of their environment, they enters the last stage of propagation, the so-called migration phase. At the beginning there is a kind of " self-cleaning " by the cell largely freed the cytoplasm by exocytosis of residual materials. The existing bi-directional grain flow is unidirectional and then the entire cytoplasm, including that of the central region flows outward. Already after only about fifteen minutes, the cytoplasm is then distributed to the extreme ends of the Retikulopodien where so usually make three or four new central areas. With increasing growth of the daughter cells may then arrive at common crossing points also to re- merger of Plasmodiennetze.
History of Research
Reticulomyxa Filosa City was discovered in the summer of 1937 in a puddle full of foliage in New York, and in 1949 first described by the botanist Ruth N. Nauss due to some features than slime mold, although she also attracted a relationship to the foraminifera into consideration. The name was suggested by Libbie H. Hyman and refers to the very long, thread-like Retikulopodien. In 1982, she was then recovered in a fish tank in the tropics houses of the Botanical Garden of the Ruhr University in Bochum, and shortly thereafter in a laboratory aquarium at Berkeley and isolated. Despite further finds but it took until 1993 the isolation of a non- directly linked to human habitat, the Möwensee in Fürstenberg / Havel.
Since it is easy to hold unlike almost all other foraminifera easily in culture and has relatively rapid life cycles, it was since its rediscovery a model organism in particular for studies on motility of the cells. The same advantages in connection with the general rare availability of foraminiferal DNA have led to Reticulomyxa Filosa was used since the first study in 1999 in many molecular genetic work on the foraminifera (eg, ), sometimes as a representative (,) for the entire group. In 2008, it was announced that the sequencing of the genome of the species is being prepared.
System
The systematic position of Reticulomyxa Filosa was unclear until the end of the 20th century. The features could be both a classification in the foraminifera as well as in the slime molds. Previous classifications of foraminifera, which are mostly based on morphological characteristics of the housing, Reticulomyxa not usually considered.
First molecular genetic studies could clarify that it is a foraminifer in the way. Later studies confirmed this and established their suspected Position in the Allogromiida. Nevertheless, their exact position within the foraminifera is also based on molecular genetic results are not yet clear as sufficient evidence for a basal position of Reticulomyxa to all other foraminifera off some Allogromia species are regarded as non- consolidated. Since they phylogenetically located in the immediate vicinity of some other housing countless species as well as species with agglutinated housings, is considered likely that the originally existing housing went evolutionarily lost again in the context of adaptation to freshwater habitats.
Apparently closely related to the species is discovered with the 1983 and 2006 first described Wobo gigas. From Reticulomyxa Filosa it differs mainly by a proteinaceous shell and a less complex networked central region. Wobo gigas was performed in older literature as another, hitherto undescribed Reticulomyxa type.