Mammalian Septins Nomenclature

The septins are a family of proteins that were first discovered in the yeast Saccharomyces cerevisiae by analysis of mutants defective in cytokinesis and bud morphogenesis. It is now clear that they are widespread and probably ubiquitous in the fungi and animals, although apparently not in plants. Most if not all septins seem to bind and hydrolyze GTP and to participate in filament formation in vitro and probably in vivo. In addition to their widespread involvement in cytokinesis, the septins seem also to be involved in vesicle trafficking and other aspects of cell surface organization, and they may have other functions as well. For various trivial historical reasons, the current nomenclature for the mammalian septins is particularly chaotic and confusing. With the field still young but attracting increasing interest, there seems to be great value in rationalizing and simplifying the septin nomenclature at this time.

In accordance with the Mouse Genomic Nomenclature Committee nomenclature, the mouse genes will be named Sept1–Sept10, and the corresponding protein products will be SEPT1–SEPT10. Although these numbers do not correspond to the genetic distances between the septins (Figure 1), they do provide an unambiguous and consistent naming system. The Human Genome Organization Gene Nomenclature Committee-approved symbols will beSEPT1–SEPT10 for the genes, and the corresponding gene products will be SEPT1–SEPT10. Although there are still too few sequences available to be certain, it seems likely that most or all septins of other vertebrates will prove to have unambiguous orthologues among the mammalian septins, in which case it would be desirable to name them by using the same system. For example, several fragments of septin genes from frog and zebrafish are available in GenBank as expressed sequence tags (ESTs), and these encode peptides that are highly related to particular mammalian septins. Therefore, we suggest that where possible other vertebrate septins be named using the same system as used for the mammalian proteins. Usually, the species being described would be obvious from the context, but it could also be indicated by adding, as a prefix, an abbreviation of the Latin binomial for the species (e.g., Xl for Xenopus laevis). For example, the frog septin A (GenBank no. AF212298), which is 89% similar in sequence to human SEPT2 but only 61% similar to the next most closely related human septin, would now be named XlSEPT2, or just SEPT2. (However, the prefix would not be a part of the official gene symbol.) At the same time, comparison of the yeast,Caenorhabditis elegans and Drosophila septins to the mammalian septins (Adam, Peifer, and Pringle, unpublished data) shows that the relationships are sufficiently complicated that the mammalian nomenclature scheme could not reasonably be applied to nonvertebrate septins.

The proposed symbols are reconciled with the previously used aliases for the mouse and human members of the septin family in Table1. This table also provides selected GenBank accession numbers for the mouse and human septins, the N- and C-terminal sequences of the longest known variants (so as to provide an unambiguous means of identification), and the human chromosome loci.

Note that some septins currently have a multitude of distinct aliases (e.g., SEPT9 names include Sint1, Sep9, E-septin, SLP-a, MSF, SepD1, and Ov/Br septin), and SEPT6 has been named both Septin 6 and Sept2, which engenders considerable confusion in the literature and in database searches. Additionally, some vertebrate septins (e.g., Cdc10 or Pnutl) have been named after Saccharomyces cerevisiae orDrosophila septins that are not true orthologues (or even the closest homologues). Finally, at least four septin genes produce multiple splice variants, and these have also sometimes been given completely different names [e.g., SEPT4 splice variants include hCDCrel-2a, hCDCrel-2b, Bradeion-α and -B, ARTS, MART, and Pnutl2(variants 1–4)]. To make the genetic origin of these variants clear, we propose using the system adopted by the Mouse and Human Genome Nomenclature Committees. In this system, splice variants are distinguished by an underscore followed by a lowercase “v” and a number, as listed in Table 1, e.g., the mouse G-septin α would be named SEPT3_v1. Finally, we propose that if new, distinct septin genes are discovered, they and their products be given a new number in the sequence (e.g., SEPT11).

FOOTNOTES