Stable reprogrammed heterokaryons form spontaneously in Purkinje neurons after bone marrow transplant

Abstract

Heterokaryons are the product of cell fusion without subsequent nuclear or chromosome loss. Decades of research using Sendai-virus or polyethylene glycol (PEG)-mediated fusion in tissue culture showed that the terminally differentiated state of a cell could be altered. But whether stable non-dividing heterokaryons could occur in animals has remained unclear. Here, we show that green fluorescent protein (GFP)-positive bone-marrow-derived cells (BMDCs) contribute to adult mouse Purkinje neurons through cell fusion. The formation of heterokaryons increases in a linear manner over 1.5 years and seems to be stable. The dominant Purkinje neurons caused the BMDC nuclei within the resulting heterokaryons to enlarge, exhibit dispersed chromatin and activate a Purkinje neuron-specific transgene, L7-GFP. The observed reprogrammed heterokaryons that form in brain may provide insights into gene regulation associated with cell-fate plasticity.

Extensive fusion of haematopoietic cells with Purkinje neurons in response to chronic inflammation

“…Nonetheless, in mice with a lethal recessive liver disease (tyrosinaemia), transplantation of wild type BMDCs restored liver function by cell fusion and rescued the mice from death 3, 9 , indicating that cell fusion can have beneficial effects. Here we report that chronic inflammation resulting from severe dermatitis or autoimmune encephalitis leads to robust fusion of BMDCs with Purkinje neurons and formation of hundreds of binucleate heterokaryons, a 10-100 fold higher frequency than previously reported 8,10,11,14 . Single haematopoietic stem cell transplants showed that the fusogenic cell is in the haematopoietic lineage and parabiosis experiments revealed that fusion can occur without irradiation.…”

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AbstractTransplanted bone marrow derived cells (BMDCs) have been reported to fuse with cells of diverse tissues [1][2][3][4][5][6][7][8][9][10][11][12][13] , but the extremely low frequency of fusion has led to the view that such events are biologically insignificant. Nonetheless, in mice with a lethal recessive liver disease (tyrosinaemia), transplantation of wild type BMDCs restored liver function by cell fusion and rescued the mice from death 3, 9 , indicating that cell fusion can have beneficial effects.

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“…cells of a number of tissues including skeletal muscle, liver, intestine, and brain 1,3,4,[8][9][10][11][12] . However, the low incidence of fusion, which increases somewhat with tissue damage 2,4,18 , has raised questions regarding its significance 19 .…”

“…In the brain, fusion of BMDCs appears to be restricted to the complex Purkinje neurons of the cerebellum 8,11,14 . Such fusion events are not limited to rodents, but have also been observed in humans 10 .…”

“…S3, S4). The rat Purkinje neuron-specific transcripts Purkinje cell protein 2 (Pcp2) 11 , vitamin D-dependent calcium-binding protein (Calb1) 11 , neuron voltage-gated potassium channel protein 1 (Kcnc1) 34 and G-substrate, (Gsbs) 35 , were detected in mouse cerebella after rat BMT (Fig. 5d).…”