Modelling Down Syndrome leukaemia using transchromosomic ES cell lines.
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AMKL (acute megakaryoblastic leukaemia) accounts for at least 50% of all
cases of acute myeloid leukaemia (AML) associated with Down Syndrome
(DS).
Every tenth neonate with DS develops Transient Myeloproliferative Disorder
(TMD), a self-regressing neoplasia with features that closely resemble AMKL.
Despite the vast majority of TMD cases self-regressing within a few weeks,
approximately 30% of DS infants with TMD develop by the age of 2-4 years a
more aggressive, full-blown AMKL. Both DS-TMD and DS-AMKL are
associated with trisomy of human chromosome 21 (HSA21) and with acquired
mutations of GATA-1 (a transcription factor essential for
erythroid/megakaryocytic lineage specification) leading to the exclusive
production of a short form of the protein known as GATA-1s. Additional
molecular events involved in the progression from TMD to AMKL remain
largely unknown.
The aim of this project was to shed new light on the critical events involved in
the pathogenesis of DS-TMD and AMKL utilizing an innovative in vitro model
that mimics Down syndrome, a murine embryonic stem cell line carrying an
extra copy of human chromosome 21 (HSA21).
Using this transchromosomic ES cell system, I explored the effect of trisomy
21 (t21) on the generation of megakaryocytes in vitro, and showed that
trisomic megakaryocyte precursors display increased levels of GATA-1
compared to euploid controls and exhibit the tendency of forming macroscopic
colonies without overt GATA1 mutations. Furthermore, I genetically
manipulated the transchromosomic ES cell system by retrovirally
4
overexpressing GATA1s and demonstrated that trisomy 21 is required for
GATA-1s to exert its full hyperproliferative potential.
The influence of the supernumerary HSA21 on the ontogenesis of
haematopoietic stem cells (HSCs) from mesodermal precursors was also
studied in the transchromosomic system. In this thesis, I present evidence that
mesodermal colonies derived from transchromosomic ES cells give rise to an
increased number of immature haematopoietic progenitors compared to
euploid controls. I demonstrate that at least two independent genes on HSA21
contribute to this effect, and that trisomy of RUNX-1 (a master regulator of
primitive haematopoiesis encoded on chromosome 21) is required for an
increased haematopoietic commitment from the mesodemal precursors.
This thesis shows that t21 influences haematopoiesis (in general) and the
megakaryocytic lineage (in particular) at several levels and that it is
responsible for an overall increase in levels of immature cells that are targets
for acquisition of further leukaemogenic mutations.
Finally, in this study I clarify the role of JAK3, a gene whose mutations have
been reported in AMKL, in the progression from TMD to AMKL.
Authors
De Vita, SerenaCollections
- Theses [3348]