Two repeated motifs enriched within some enhancers and origins of replication are bound by SETMAR isoforms in human colon cells

Setmar is a gene specific to simian genomes. The function(s) of its isoforms are poorly understood and their existence in healthy tissues remains to be validated. Here we profiled SETMAR expression and its genome-wide binding landscape in colon tissue. We found isoforms V3 and V6 in healthy and tumour colon tissues as well as incell lines. In two colorectal cell lines SETMAR binds to several thousand Hsmar1 and MADE1 terminal ends, transposons mostly located in non-genic regions of active chromatin including in enhancers. It also binds to a 12-bp motifs similar to an inner motif in Hsmar1 and MADE1 terminal ends. This motif is interspersed throughout the genome and is enriched in GC-rich regions as well as in CpG islands that contain constitutive replication origins. It is also found in enhancers other than those associated with Hsmar1 and MADE1. The role of SETMAR in the expression of genes, DNA replication and in DNA repair are discussed.

Transposase concentration controls transposition activity: myth or reality?

Deciphering the mechanisms underlying the regulation of DNA transposons might be central to understanding their function and dynamics in genomes. From results obtained under artificial experimental conditions, it has been proposed that some DNA transposons self-regulate their activity via overproduction inhibition (OPI), a mechanism by which transposition activity is down-regulated when the transposase is overconcentrated in cells. However, numerous studies have given contradictory results depending on the experimental conditions. Moreover, we do not know in which cellular compartment this phenomenon takes place, or whether transposases assemble to form dense foci when they are highly expressed in cells. In the present review, we focus on investigating the data available about eukaryotic transposons to explain the mechanisms underlying OPI. Data in the literature indicate that members of the IS630-Tc1-mariner, Hobo-Ac-Tam, and piggyBac superfamilies are able to use OPI to self-regulate their transposition activity in vivo in most eukaryotic cells, and that some of them are able to assemble so as to form higher order soluble oligomers. We also investigated the localization and behavior of GFP-fused transposases belonging to the mariner, Tc1-like, and piggyBac families, investigating their ability to aggregate in cells when they are overexpressed. Transposases are able to form dense foci when they are highly expressed. Moreover, the cellular compartments in which these foci are concentrated depend on the transposase, and on its expression. The data presented here suggest that sequestration in cytoplasmic or nucleoplasmic foci, or within the nucleoli, might protect the genome against the potentially genotoxic effects of the non-specific nuclease activities of eukaryotic transposases.

Novel approach for the development of new antibodies directed against transposase-derived proteins encoded by human neogenes

Molecular domestication of several DNA transposons has occurred during the evolution of the primate lineage, and has led to the emergence of at least 42 new genes known as neogenes. Because these genes are derived from transposons, they encode proteins that are related to certain recombinases, known as transposases. Consequently, they may make an important contribution to the genetic instability of some human cells. In order to investigate the role of these neogenes, we need to be able to study their expression as proteins, for example in tumours, which often provide good models of genetic instability. In order to perform such studies, polyclonal antibodies directed against the proteins expressed by neogenes are obtained using a recently developed new method of Nanospheres/DNA immunisation in laboratory mammals. In this chapter, we describe a fully integrated process of producing antibodies that consists of a series of steps starting with the preparation and synthetic formulation of plasmids encoding neogenes, and culminating in the final production and confirmation of the quality of these polyclonal antibodies.