PgmNr P2053: Transposase genes are actively expressed in vespertilionid bat somatic tissues.

Authors:
Rachel Cosby; Ellen Pritham


Institutes
University of Utah, Salt Lake City, UT.


Abstract:

Transposition is often deleterious, and is generally repressed by the host in both germline and somatic tissues. Despite this, transposition does occur, and studies of various elements from fly (P element, hobo) indicate that transposition is most common in the germline. Recent studies have challenged this idea in mammals, demonstrating that transposition occurs in somatic tissues, such as brain and tumor tissue. Most of these studies were done in human, where only LINE-1 retrotransposons remain active. Thus, the extent of somatic transposable element (TE) activity in mammals is unexplored. DNA TE activity in mammals is understood even less, due to their recent extinction in most lineages. DNA transposons are active in many other vertebrates, indicating that mammals are the exception, rather than the rule. Notably, the Vespertilionid (vesper) bat family, has experienced numerous, recent waves of DNA TE activity in conjunction with retrotransposon activity. Here we identify expressed, full-length, putatively active transposase genes in vesper bat tissues. We performed RNA-sequencing and de-novo transcriptome assembly on liver, kidney, and testis tissues and fibroblast cell lines obtained from four vesper bat species, Myotis lucifugus, M. occultus, M. velifer, and Eptesicus fuscus. We also incorporated publicly available datasets for kidney, liver, and brain from another vesper bat, M. brandtii. We then compared existing transposase protein coding sequence to predicted open reading frames (ORFs) in our transcriptome dataset in order to identify transcripts with intact transposase ORFs. We also searched for intact transposase domains using HMMER. In doing so, we identified several expressed transposase transcripts, including both DNA TEs (hAT, PiggyBac, others) and retrotransposons (endogenous retroviral pol, gag, and env genes, and LINE-1 transposase), across all vesper bats examined. Many of these elements have been predicted to be active in vesper bats previously, but often no full-length elements were found, indicating that utilizing de-novo transcriptome data may identify low frequency events in the population as well as overcome difficulties due to poor genome assemblies. Overall, our data strongly implies that somatic transposase expression is common in bats, and that these TEs may be actively transposing in somatic tissue, perhaps due to a lack of regulation in somatic tissues. Thus, the contribution of TE expression and transposition to the somatic transcriptome and genome of mammals may be greater than initially anticipated. Further, expression in somatic tissues may favor horizontal transfer, granting TEs another avenue to propagate outside the germline.