另一個題外話: choanoglafellate (wiki : https://en.wikipedia.org/wiki/Choanoflagellate), a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals.
The cell body of many choanoflagellates is surrounded by a distinguishing extracellular matrix or periplast.
A free living SPERM ? with a Coat/ a reinforced, moving home?
The choanoflagellates feed on bacteria. Movement of the flagellum draws water through the collar, and bacteria and detritus are captured by the microvilli and ingested.Water currents generated by the flagellum also push free-swimming cells along, as in animal sperm.
A model of S. rosetta life history. Fig 2 from "Cell differentiation and morphogenesis in the colony-forming choanoflagellate Salpingoeca rosetta" by Dayel et al., 2011. (doi:10.1016/j.ydbio.2011.06.003)
Analysis on molecular phylogenetic analysis on SSU, LSU, a-tubulin and hsp90 found that choanoflagellates are strongly supported as monophyletic and confirm their position as the closest known unicellular living relative of animals.
Two choanoflagellate species have had their genomes fully sequenced, with another two species having had transcriptome data published.
- Monosiga brevicollis (ensembl genome) : 41.6 Mb, assembled in 218 supercontigs
- Salpingoeca rosetta (ensembl genome ): 55 Mb, assembled in 154 supercontigs
Previously, Choanoflagellida was divided into these three families based on the composition and structure of their periplast; now with classification based on molecular phylogenetics. The choanocytes (also known as "collared cells") of sponges (considered among the most basal metazoa) have the same basic structure as choanoflagellates. Collared cells are found in other animal groups, such as ribbon worms,[17] suggesting this was the morphology of their last common ancestor.
The SIT gene family shows little or no homology to any other genes, even to genes in non-siliceous choanoflagellates or stramenopiles. This suggests that the SIT gene family evolved via a lateral gene transfer event between Acanthoecids and Stramenopiles.
Broad Institute Project:
Origins of Multicellularity Database
The Origins of Multicellularity Project was funded by the NHGRI and is described in a white paper and a recent publication.
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