Crossley is interested in
gene regulation. He studied an unusual genetic disorder termed
Haemophilia B Leyden where patients recover after puberty. The condition results from mutations that disrupt the control region of the clotting
factor IX gene. A
testosterone-responsive element accounts for post-pubertal recovery. He has also investigated abnormal patterns of
globin gene expression and his work on mutations associated with the lifelong expression of the
fetal haemoglobin gene may help in the treatment of
thalassemia and
sickle cell anaemia. He is using
CRISPR-mediated gene editing to introduce beneficial mutations in cell lines as models for treating genetic diseases. Clinical trials by major gene editing companies are now introducing mutations that his lab described. This recent work is considered highly significant. Because co-inheriting mutations that generate lifelong fetal globin expression (so-called
Hereditary Persistence of Fetal Hemoglobin or HPFH mutations) essentially prevents
Sickle Cell Disease and
beta-thalassemia, understanding the molecular mechanisms and mimicking them by
CRISPR-gene editing has become the major therapeutic strategy. Crossley’s lab made three seminal contributions: he showed all the natural point mutations in the fetal globin gene promoter that cause HPFH either create new sites for gene activating proteins or disrupt sites for repressors, BCL11A or ZBTB7A. This is how he discovered ZBTB7A was one of the two major fetal globin repressors, and is how BCL11A was found to directly repress the fetal globin gene. There are many different deletions but they all remove the beta-globin gene promoter. This means that the fetal globin promoter no longer has competition from the beta-globin promoter and it can now access the large enhancer, the Locus Control Region. This is significant as epigenetic editing does not cut the DNA so may be even safer than standard CRISPR-editing and base editing. He is also known for the initial identification and cloning of a significant number of genes encoding
DNA-binding proteins:
KLF3,
KLF8,
KLF17, EOS
IKZF4, PEGASUS IKZF5, and their associated
co-regulators: FOG1
ZFPM1, FOG2
ZFPM2, and
CTBP2. These genes encode gene regulatory proteins (also known as
transcription factors) and their co-regulators that turn genes on and off. Identifying the proteins involved was an important foundational step in our understanding of how the genome is regulated. Several additional discoveries are of note: in the early 2000s his lab noted that several gene regulatory proteins that turn genes off contained SUMOylation motifs within their repression domains. In 2023 a comprehensive study of the 2000 gene regulatory proteins in humans in
Nature concluded that indeed repression domains do typically have SUMOylation sites, thus linking SUMOylation with gene repression. The second discovery involves zinc fingers, small protein domains usually known for DNA-binding. His lab was involved in showing that zinc fingers can also mediate protein-protein interactions, best characterized by the interaction between the blood gene regulatory proteins, GATA1 and Friend of GATA. He has been the advisor to the Human Genome Nomenclature Committee on the naming of the Kruppel-like Factor family and as well as identifying and cloning the genes for KLF3, KLF8, and KLF17, he discovered the cross-regulation between KLF1, KLF3, and KLF8, illustrating both redundancy and inter-dependency within this gene family. ==Other activities==