The MLL-side twin of the 1998 anti-AF4 result: in 1997 the same punctate nuclear pattern was seen with and without an 11q23 translocation, and the authors said so
also called Butler 1997 HRX localisation · HRX punctate nuclear structures · anti-MLL immunocytochemistry attribution
In 1997 a group made antibodies to the normal MLL protein and looked at leukemia cells. On a gel the antibodies separated the fusion protein from the normal one by size; under the microscope the picture looked the same whether or not the cell carried the translocation, and the authors themselves wrote that this rules out using the microscope to diagnose the disease.
The same thing, for a scientist
This graph's fusion-attribution audit established that the only endogenous immunofluorescence of a KMT2A fusion - the 1998 anti-AF4 study - is unattributable rather than negative, because a shared-epitope polyclonal images wild-type AF4 and the minority fusion species together [E1]. The same shape exists a year earlier **from the MLL side and with monoclonal as well as polyclonal reagents**, and it was not cited anywhere in this graph before this cycle. Butler and colleagues blotted protein extracts from cells carrying t(11;19) and t(4;11) and resolved chimeric HRX proteins at the sizes predicted from the fusion mRNAs - the size dimension doing the attribution. They then imaged the same reagents and found a punctate nuclear distribution of wild-type and chimeric HRX alike, 'in cells with and without 11q23 translocations', and drew the explicit methodological conclusion that this 'precludes an immunocytochemical approach for diagnosis of leukemias bearing 11q23 structural abnormalities' [E2]. That is the audit's finding, stated by the original authors, twenty-nine years before the audit. It means the punctate-nuclear description of KMT2A fusions rests on two independent experiments that each say, in their own words, that they cannot tell the species apart.
What was attributable and what was not, in the same paper
The paper contains both halves of the size-dimension rule in one place.
Attributable. Western blots of extracts from t(11;19) and t(4;11) cells showed chimeric HRX proteins whose migration matched the size predicted from each line's own fusion mRNA 2. Predicting the band from the patient's transcript and then finding it is a genuine fusion-specific measurement, and it is the same design the 1998 AF4 paper used for its 240-versus-125/145 kDa resolution 1.
Not attributable. Immunocytochemistry with the same reagents gave a punctate nuclear pattern in cells with and without the translocation. Nothing in the image distinguishes the chimera from wild-type HRX, and the paper says so.
The authors were making a diagnostic point rather than a mechanistic one - they wanted to know whether anti-HRX staining could flag 11q23 disease, and concluded it cannot because HRX is widely expressed across human tissues with strongest reactivity in cerebral cortex, kidney, thyroid and lymphoid tissue 2. The mechanistic consequence is the one that matters here, and it appears to have gone unremarked for three decades.
Why two independent unattributable images are worse than one
A reader encountering the punctate description twice - once from the AF4 side in 1998 1 and once from the MLL side in 1997 2 - will reasonably treat it as replicated. It is replicated, but what is replicated is the observation that the picture does not change, which is the expected result in both the 'fusion goes where the parent goes' model and the 'fusion is invisible against the parent' model.
Two experiments that cannot distinguish two models do not distinguish them any better for being two. The graph should therefore hold the punctate claim at the confidence of a non-measurement, not at the confidence of a replicated finding.
The abundance datum from the AF4 side sharpens this: the fusion is the less abundant species 1. A minority species contributes proportionally less to an image than to a blot lane, so the imaging failure is not symmetric with the blotting success.
What would convert it
Nothing about the 1997 or 1998 images can be rescued, because the information was never collected. Three designs restore attribution and all are described elsewhere in this graph: an epitope tag knocked in at the endogenous fusion allele; a degron that subtracts the fusion's contribution to a signal 3; or - cheapest and needing no new reagent - fractionate and blot, which keeps the size dimension that imaging discards.
The constraint on tagging is real and documented: an N-terminal tag on MLL::AF9 did not reproduce the untagged construct's leukaemogenesis kinetics, which the authors attribute to interference with chromatin localisation because the DNA-binding and menin-binding modules are N-terminal; only the C-terminally tagged construct behaved like the parent 3. For a KMT2A fusion the tag goes on the partner end.
| readout | immunocytochemistry + Western blot, same reagents |
|---|---|
| size dimension blot | true |
| size dimension image | false |
| attribution verdict | blot attributable, image unattributable |
| authors own statement | precludes an immunocytochemical approach for diagnosis of leukemias bearing 11q23 structural abnormalities |
translocations examined
[ "t(4;11)", "t(11;19)" ]
- Any pharmacodynamic assay that reads fusion localisation by immunofluorescence in patient cells inherits this failure, and would score a drug effect on wild-type KMT2A as an effect on the fusion.
- A trial correlative endpoint built on 'fusion redistribution by imaging' would be uninterpretable, and the 1997 authors said as much about the diagnostic version of the same idea.
- Which cell lines were imaged in the 1997 study, and is the full text reachable by any non-PMC route?
- Did either the 1997 or the 1998 study co-stain a compartment marker, or was the punctate pattern described without reference to any named structure?
- Is there a cell type in which wild-type KMT2A is low enough that a shared-epitope image would be fusion-dominated?
- E1strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
In t(4;11) cells anti-AF4 polyclonals resolve the fusion at about 240 kDa from wild-type AF4 at 125 and 145 kDa on a blot, but in the microscope t(4;11) and non-t(4;11) leukaemic cells show a similar punctate nuclear pattern, and the fusion is the less abundant species.
AF4 encodes a ubiquitous protein that in both native and MLL-AF4 fusion types localizes to subnuclear compartments · Li Q, et al. · Blood 1998What this evidence cannot show
Abstract-level plus this graph's fusion-attribution audit of the same paper. No PMCID by the Europe PMC core route and no DOI in the PubMed record.
Evidence that argues against this (1)
- In a transfected system, where the fusion is the only species carrying the partner epitope, chimeric ALL-1 proteins do show a punctate distribution that maps to defined N-terminal elements - so the punctate pattern is a real property of the protein family, not only a wild-type background. Yano T et al. 1997
- E2strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
Western blots of extracts from cells carrying t(11;19) and t(4;11) showed chimeric HRX proteins migrating at the sizes predicted from the fusion mRNAs, while immunocytochemistry with the same polyclonal and monoclonal reagents showed a punctate nuclear distribution of wild-type and chimeric HRX in cells with and without 11q23 translocations - which the authors state precludes an immunocytochemical approach to diagnosis.
The HRX proto-oncogene product is widely expressed in human tissues and localizes to nuclear structures · Butler LH, et al. · Blood 1997What this evidence cannot show
Abstract only. No PMCID by the Europe PMC core route, no DOI in the PubMed record, and the publisher page returns HTTP 403, so routes 2, 3 and 4 of the unreadable test were not reachable; the cell lines used for imaging are not named in the abstract. Reagent specificity was confirmed on cells transfected with HRX-ENL, which is itself an overexpression control.
Evidence that argues against this (1)
- The wide tissue expression that drives the diagnostic conclusion also means the imaging comparison was made against an abundant wild-type background everywhere; a cell type with unusually low wild-type KMT2A would be a more favourable, and untested, setting for the same experiment. Yano T et al. 1997
- E3strong confidence 4 of 5: Replicated in peer-reviewed work by more than one group.paper
An N-terminal tag on MLL::AF9 did not reproduce the untagged construct's leukaemogenesis kinetics, attributed to interference with chromatin localisation because the DNA-binding and menin-binding motifs are N-terminal, and only the C-terminally tagged construct behaved like the parent; the degron system then allows the fusion's contribution to a signal to be subtracted.
MLL::AF9 degradation induces rapid changes in transcriptional elongation and subsequent loss of an active chromatin landscape · Olsen SN, et al. · Molecular cell 2022What this evidence cannot show
Mouse MLL::AF9 model, not human KMT2A::AFF1, and the kinetic failure is inferred to be a localisation effect rather than measured as one. The tag-placement constraint is nonetheless the strongest published guidance for designing an attributable imaging experiment in this family.
Evidence that argues against this (1)
- Because the N-terminal tag failure was not itself read out as a localisation change, an alternative explanation - altered taspase1 processing or protein stability - is not excluded, so the design rule rests on an inference. Liu H et al. 2007
- ← related toKMT2A / MLL1 — the gene that breaks
the punctate nuclear image of KMT2A in translocated cells is unattributable by its own authors
the MLL-side twin of the same unattributable-image shape, one year earlier
the audit's conclusion stated by the original authors in 1997
- related to →KMT2A / MLL1 — the gene that breaks
wild-type HRX/KMT2A is punctate and widely expressed, which is what makes the fusion invisible in an image
the same paper's blot half shows the size dimension working where the image half fails
- related to →KMT2A::ELL (MLL-ELL), t(11;19)(q23;p13.1)
t(11;19) extracts were among those blotted, giving a second translocation with a size-resolved chimeric band
a second way a fixed-cell image misleads: cell-cycle averaging on top of species ambiguity
a 1997 paper reaching the same conclusion for diagnostic immunocytochemistry