NTRs: Reservosome and its components

[Achchuthan]

Accession: GO:xxxxxx Name: reservosome Ontology: cellular_component Definition: Reservosome is a large membrane-bound endocytic organelle present only in members of the Schizotrypanum subgenus of the Trypanosoma genus and is defined as the site of storage of endocytosed macromolecules and lysosomal enzymes. It is found at the posterior end of epimastigote forms of Trypanosoma cruzi, but absent in amastigotes and trypomastigotes. is_a: GO:0005770 ! late endosome Taxonomic restriction: NCBITaxon:47570 ## Schizotrypanum Source: PMID:12204365, PMID:15521631, PMID:18452191, PMID:19288526, PMID:21818313, PMID:22425988

Accession: GO:xxxxxx Name: reservosome lumen Ontology: cellular_component Definition: The volume enclosed by the membranes of a reservosome. part_of: GO:xxxxxx ! reservosome Taxonomic restriction: NCBITaxon:47570 ## Schizotrypanum

Accession: GO:xxxxxx Name: reservosome matrix Ontology: cellular_component Definition: A matrix composed of planar membranes, vesicles and lipid inclusions within the reservosome. part_of: GO:xxxxxx ! reservosome lumen Taxonomic restriction: NCBITaxon:47570 ## Schizotrypanum Source: PMID:18452191, PMID:21818313

Accession: GO:xxxxxx Name: reservosome membrane Ontology: cellular_component Definition: The lipid bilayer surrounding a reservosome. is_a: GO:0098805 ! whole membrane bounding_layer_of: GO:xxxxxx ! reservosome Taxonomic restriction: NCBITaxon:47570 ## Schizotrypanum Source: PMID:12204365, PMID:18452191, PMID:19288526

[pgaudet]

Hi @Achchuthan

I wonder, can you use ' GO:0000322 storage vacuole'? We could give it a 'narrow synonym' reservosome. Or are there other Schizotrypanum storage vacuoles you also want to be able to distinguish?

Thanks, Pascale

[Achchuthan]

HI @pgaudet,

Thank you very much for your question regarding using reservosome as a narrow synonym for storage vacuole.

To start with, there are two specialized types of storage vacuoles present in Trypanosomes, particularly T. cruzi. The first one is acidocalcisome containing polyphosphates with bound calcium. It is represented with GO:0020022. The second is reservosome - site of accumulation of endocytosed macromolecules, very rich in cysteine proteinase (PMID:11028107).

Reservosome is a lysosome -related organelle at the last step of endocytosis and is responsible for cellular digestion of endocytosed material and for providing substrates to cellular metabolic demands (PMID:21818313). In this regard, it also functions similar to late endosome. The storage vacuole is therefore a potential parent term for both acidocalcisome and reservosome.

Thanks & best wishes, Achchuthan

[hdrabkin]

Hi @Achchuthan ; can you tell us how this term is different from late endosome other than the species differentia (trypanosome)?

[Achchuthan]

Hi @hdrabkin,

Thanks for your question.

Reservosome is similar to late endosome as it is a rounded organelle, acidic, part of the endocytic pathway and a pre-lysosomal compartment that is formed when cargo is delivered from early endosomes.

But, it is different from late endosome as it serves as a storage vacuole and store nutrients including heme and lipids such as cholesterol from the insect mid-gut during the epimastigote stage as the parasite's environment is full of blood meal. Once the nutrients become scarce, differentiation of epimastigotes into metacyclic-trypomastigotes (process of metacyclogenesis) is triggered and the nutrients from reservosomes are consumed. Lipid inclusions in reservosomes seems to be a unique feature of this organelle, although it is endsome-like.

Thanks & best wishes, Achchuthan

[hdrabkin]

Hi, So 'Lipid inclusions in reservosomes seems to be a unique feature of this organelle, " Do you mean only the reservosome has lipid inclusions? and other endosomes do not?

[Achchuthan]

Hi @hdrabkin, Cholesterol derived from LDL is transported from plasma membrane in the endocytic pathways in other organisms as well and other late endosomes do have these LDL-derived cholesterol. However, the lipid composition of this organelle, the disk or rod-like rectangular shapes of lipid inclusions and the phospholipid monolayer surrounding these lipid inclusions (crystallin-like nature) seem to be unique features.

In addition, the purpose of this organelle is storage of lipids until starvation (at this point differentiation into another lifer cycle stage occurs) rather than just delivery of lipids to the cell.

Thanks, Achchuthan

[deustp01]

"Storage" sounds like a reliable difference - the other features also don't fit the textbook description of a mammalian late endosome processing stuff for degradation, but I'm not sure they can't occur sometimes. The textbook certainly does not allow mammalian endosomes to persist as a storage form of lipids or anything else: they turn over briskly.

[pgaudet]

But then the reservosome is not an endocome; its a storage vacuole derived from an endosome; is this correct ?

Pascale

[Achchuthan]

Hi @pgaudet , Yes, your definition that reservosome is a storage vacuole derived from an endosome is right. Hence, it shares some features of endo/lyso-some such as it is acidic and it is a product of endocytic pathway. However, its different as its role is storage of lipids and heme.

Thanks, Achchuthan

[hdrabkin]

So really is_a: GO:0005770 ! late endosome maybe should be is_a: storage vacuole?

[Achchuthan]

I forgot to bring one point: In addition to being storage vacuole, it also seems to have lytic function as it has cysteine proteinase. So, it is a dual functioning vacuole with both storage and lytic function.

Should we have both storage vacuole and lytic vacuole (GO:0000323) as parents?

[hdrabkin]

So are all reservosomes capable of being both storage vacuole and lytic vacuole? (any/all have cysteine proteinase, etc.)?

[Achchuthan]

Hi @hdrabkin, All reservosomes are capable of being both storage vacuole (stores lipids) and lytic vacuole (have enzymes of protein digestion including cysteine proteinase). Thanks, Achchuthan

[hdrabkin]

Ok, I think we will put this in with dual parentage

[hdrabkin]

reservosome GO:0106123 reservosome lumen GO:0106124 matrix GO:0106125 membrane GO:0106126

[hdrabkin]

Argh; forgot taxon constraint; may take a while as I think this one needs to be imported. NCBITaxon:47570 ## Schizotrypanum

[Achchuthan]

Thanks a lot @hdrabkin

[hdrabkin]

Added taxon constraints; Thanks @balhoff ! Done