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This also means that the function of a particular lncRNA using a mouse model of metastasis for instance,
does not always imply that the mechanism of action of those lncRNAs function similarly in human cells.
For instance, the use of genetically engineered mouse models (GEMMs) that have a propensity to develop
metastasis may provide some useful information yet may not provide a complete picture regarding the
mechanisms by which a specific lncRNA promotes metastasis in human systems. Therefore, additional
technologies will be required to assess the functionality of metastatic-specific lncRNAs. For instance, the use
of humanized mouse models, 3D culture systems, and use of conditionally reprogrammed cells from human
tissue, all will aid investigators in determining the bona fide relevance of functionally conserved lncRNAs.

In many cases lncRNAs are expressed at lower abundance than cytoplasmic mRNA, thereby making it
difficult to assess whether lncRNAs are functionally relevant, or present as a result of leaky transcriptional
activity. As an example, lncRNAs can regulate the processing of nascent transcripts generated from RNA
polII-based transcription. These lncRNAs may only number a few copies in the cell at any given time yet
can bind in a 1:1 stoichiometric relationship with the nascent mRNA altering the stability of the newly
synthesized RNA molecule. Technologies such as global run on sequencing , which is a sensitive and
[187]
high throughput type of nuclear-run on assay, have been developed to specifically determine the relevant
abundance of a particular lncRNA binding these nascent transcripts. Additionally, techniques such as high-
throughput sequencing of RNAs isolated by crosslinking immunoprecipitation (CLIP) and cross-linking,
[188]
ligation and sequencing of hybrids (CLASH) have been utilized to gauge the abundance, enrichment,
[189]
and/or composition of composition of ncRNAs within particular RNA-RBP cytoplasmic complexes. As
sequencing technology develops and the cost to perform these analyses decrease, the utilization of these
biochemical approaches coupled with these high-throughput sequencing methods will pave the way for new
discoveries regarding lncRNA function.

Despite these challenges, it is clear that lncRNAs play a crucial role in driving a metastatic phenotype,
and in particular regulate the initiating steps of metastasis such as EMT. Given EMT is the process of
cell fate switching, or reactivation of embryogenic programs that convert epithelia cells to those harboring
a mesenchymal phenotype, the continued approach of utilizing reductionist-based investigations within
well-defined model systems will help in elucidating the mechanisms by which individual lncRNAs regulate
the underlying biology of metastasis. Given the advances in sequencing technology as well as a renewed
scientific interest in lncRNA biology, the number of publication discussing the role of lncRNAs in metastasis
will most likely double in the next year. The continued demand for reliable biomarkers of metastasis will also
fuel research towards the development of prognostic and predictive indicators for patients with high grade
tumors harboring metastatic dissemination. In conclusion, the lncRNA field is certainly in its infancy, yet
is considered to be the wild-west of the post-genomic era and has the potential to unlock the key to some of
the most prevalent challenges associated with treating patients with metastatic disease.

DECLARATIONS
Acknowledgments
We thank Kimberly N. Kelly at BioCT Innovation Commons, as well as Drs. Garret Barr and Ann Yezerski
Gilmor at King’s College for providing the resources and office space required for the writing of this
manuscript.

Authors’ contributions
Conception and design: Adams BD, Reed IG, Alexander A, Willetts L, Habibian M
Financial support: Adams BD
Literature search, manuscript preparation and writing: all authors
Manuscript editing: Adams BD, Reed IG, Willetts L
Manuscript review: all authors