RESUMEN
Crinoids (Echinodermata) exhibit unique morphological and behavioral characteristics that facilitate a wide range of symbiotic relationships with diverse organisms. Our comprehension of their interactions with microscopic copepod crustaceans is, however, still in a nascent and fragmented state. Here, we review and discuss the 166 literature records to date in which a total of 39 copepod species in 6 families have been reported in association with 33 species of the crinoid order Comatulida. Many of these associations have been reported just once. The respective localities cover 5 of the World Ocean's 12 ecoregions, with a notable concentration of both host and symbiont diversity in the Central and Western Indo-Pacific. In contrast, the documentation of copepod-crinoid associations in the Atlantic appears markedly limited. Copepods have been found predominantly in ectosymbiotic relationships with crinoids, with a lower incidence of endosymbiosis. Copepods of the genera Collocheres Canu, 1893 and Pseudanthessius Claus, 1889 are particularly prominent in the list, and the comatulid family Comatulidae displays the most diverse assortment of copepod associations. The current scope of knowledge encompasses a mere 5% of the potential crinoid host diversity, underscoring the need for more extensive research in this area.
RESUMEN
The kinetoplastids are unicellular flagellates that derive their name from the 'kinetoplast', a region within their single mitochondrion harboring its organellar genome of high DNA content, called kinetoplast (k) DNA. Some protein products of this mitochondrial genome are encoded as cryptogenes; their transcripts require editing to generate an open reading frame. This happens through RNA editing, whereby small regulatory guide (g)RNAs direct the proper insertion and deletion of one or more uridines at each editing site within specific transcript regions. An accurate perspective of the kDNA expansion and evolution of their unique uridine insertion/deletion editing across kinetoplastids has been difficult to achieve. Here, we resolved the kDNA structure and editing patterns in the early-branching kinetoplastid Trypanoplasma borreli and compare them with those of the well-studied trypanosomatids. We find that its kDNA consists of circular molecules of about 42 kb that harbor the rRNA and protein-coding genes, and 17 different contigs of approximately 70 kb carrying an average of 23 putative gRNA loci per contig. These contigs may be linear molecules, as they contain repetitive termini. Our analysis uncovered a putative gRNA population with unique length and sequence parameters that is massive relative to the editing needs of this parasite. We validated or determined the sequence identity of four edited mRNAs, including one coding for ATP synthase 6 that was previously thought to be missing. We utilized computational methods to show that the T. borreli transcriptome includes a substantial number of transcripts with inconsistent editing patterns, apparently products of non-canonical editing. This species utilizes the most extensive uridine deletion compared to other studied kinetoplastids to enforce amino acid conservation of cryptogene products, although insertions still remain more frequent. Finally, in three tested mitochondrial transcriptomes of kinetoplastids, uridine deletions are more common in the raw mitochondrial reads than aligned to the fully edited, translationally competent mRNAs. We conclude that the organization of kDNA across known kinetoplastids represents variations on partitioned coding and repetitive regions of circular molecules encoding mRNAs and rRNAs, while gRNA loci are positioned on a highly unstable population of molecules that differ in relative abundance across strains. Likewise, while all kinetoplastids possess conserved machinery performing RNA editing of the uridine insertion/deletion type, its output parameters are species-specific.