About the blog author: Yvain Desplat graduated with Master of Science from Nova Southeastern University in Florida (August, 2020). His thesis work focused on characterizing gene responses after oil and dispersant exposure in marine sponges (Cinachyrella spp.) to establish the genus Cinachyrella as a bioindicator in the face of environmental challenges. He currently works as a Research Associate II at JumpCode Genomics Inc in San Diego, California.
Marine sponges (Phylum Porifera) are rarely used as experimental models, but their development as such offers several benefits. Besides occurring in oceans worldwide and being one of the earliest emerging metazoan taxa, sponges have a simple, basic physiology with some features that can mirror more complex animals (Riesgo et al. 2014; Feuda et al. 2017). However, very little is known about those organisms from a genomics perspective. To date, only two genomes are publicly available: Amphimedon queenslandica (Fernandez-Valverde et al. 2015) and Ephydatia muelleri (Kenny et al. 2020). A. queenslandica was the first ever poriferan genome to be assembled with the colossal worked achieved by Srivastava et al. (2010) and Fernandez-Valverde et al. (2015). These teams showed how tricky the de-novo assembly of the genome and transcriptome of such an understudied phylum really is.
The difficulty in assembling such genomics resources primarily results from two main reasons: a) sponges are known to be highly symbiotic organisms, with some species having symbiotic microbial communities composing large proportions of the sponge biomass (called in the field High Microbial Abundance sponges or HMA), which renders downstream analysis cumbersome, and b) correct identification of specimens is sometimes tricky as even taxonomic genetic markers are not always detected.
In our new Journal of Heredity article (Desplat et al, 2022), we decided to study a genus of marine sponges found globally, Cinachyrella, in order to gauge the genetic responses in the face of environmental stress. However, besides the lack of genome or transcriptome resources for this species, three species of Cinachyrella are present on Florida’s reef tract: Cinachyrella alloclada, Cinachyrella apion, and Cinahcyrella kuekenthali. Those three sponge species are all HMA sponges and are easily not distinguishable through the eye (Shuster et al. 2017). Hence, genetic marker analysis is required to characterize the species and perform any study. In Cinachyrella, the Group I intron sequence motif LAGDIGLAD is usually used to call correct taxonomy, but even then, this intron is challenging to PCR amplify and not always present in the samples. The other solution is to use house-keeping genes such as EF1A (elongation factor 1A).
Consequently, in an effort to extend genomics resources for the Phylum Porifera, we here report the assembly of the holo-transcriptome of the HMA sponge Cinachyrella alloclada (identified through EF1A gene characterization). The assembly consisted of 1,194,291 contigs among which a total of 39,813 transcripts identified as sponge related. The large majority of transcripts (36,459) was identified as similar to the sponge Amphimedon queenslandica. Thus, a large difference exists between the number of hits matching a sponge and the total number of annotated genes. This finding could be explained by the well documented presence of microbial symbionts, composing up to 60% of total organismal biomass (Webster and Thomas 2016; Lopez 2019).
Our effort adds a new dataset in the Order Tetractinellida, consistent with previous sponge RNAseq studies (Manousaki et al. 2019) and is available on the NCBI repository under the accession GJAZ00000000 under BioProject PRJNA663558.
References
Webster NS, Thomas T. (2016) The Sponge Hologenome. MBio, 7: doi: 10.1128/mbio.00135-16