Here’s a thread about the #nucleus… no, Professor Ernest Rutherford, not the atomic nucleus that you discovered with your alpha particles back in 1911.😉 This is about *cell* nuclei and all their weird and wonderful forms, in blood cells and beyond. #HematologyTweetstory 31! /1 
Cell nuclei were first drawn by Dutch microscopy pioneer Antonie van Leeuwenhoek circa 1719 (pictured), and discussed as distinct structures in 1804 by botanist Franz Bauer (below with green jacket), then clearly described in 1831 by botanist Robert Brown (below, with bowtie)./2
Brown first called the nucleus the “cell areola” – which suggests he may have observed nucleoli as well, although he didn't mention them (they would have been just at the limit of his microscope's resolving ability). Probably a good thing that term didn’t stick, though.../3
There was much debate about just what nuclei were in the mid- to late 1800s. It soon became obvious that they split apart when cells divided. But... why? The reason wouldn’t become clear until the 20th century with the linking of mitosis (1882, Flemming) to Mendelian genetics./4
Blood cells are recognizable by their nuclear patterns. Most neutrophils have 3 or 4 lobes connected by thin strands of chromatin-free nucleoplasm, while eosinophils are usually bilobed. Basophil nuclei have 2 lobes, but granules are so dark it can sometimes be hard to see./5
The “mononuclear” leukocytes include lymphocytes and monocytes. Lymphocyte nuclei are usually more condensed and round. Monocyte nuclei (which are actually usually “bilobed” - cleaved or kidney shaped - not “mono” lobed!) change shape when they differentiate into macrophages./6
The distinction between "polymorphonuclear" vs. "mononuclear" leukocytes is often credited to Ilya Metchnikoff, who discovered macrophages in 1882 and received the 1908 Nobel with Paul Ehrlich. I always found it puzzling why monocytes are so named given their bilobed nucleus./7
One of the most impressive cells in all of microscopy is the megakaryocyte. For still unclear reasons – perhaps to do with its unique way of making platelets - megs get huge and undergo endomitosis/nuclear endoreduplication, so can have up to 128N DNA all smooshed together./8
Here’s an amusing Boston-centric way (in the "Hub of the Universe" tradition of Oliver Wendell Holmes) of depicting megakaryocyte maturation from the Katya Ravid lab @BU_Tweets 😉/9
Hepatocytes do the endomitosis thing, too, but rarely exceed 8N ploidy - and, in contrast to megakaryocytes, the nuclei are widely separated./10
Sometimes mistaken for a megakaryocyte by new histology students are giant multinucleated Langhans-type macrophages, which can be seen in granulomatous disorders. These arise differently: not endomitosis, but fusion of multiple epitheloid macrophages, mediated by CD40/CD40L. /11
By the way, those are *Langhans* cells, named after bearded 19th century German pathologist Theodor Langhans (1839-1915; depicted below left), not *Langerhans* cells, named after bearded 19th century German pathologist Paul Langerhans (1847-1888; depicted below right).🧔🏻/12
Blasts are recognizable by their prominent nucleolus. Stages of leukocyte precursors are defined in part by the degree of nuclear indentation. Red cells, of course, normally completely extrude their nuclei during development – but sometimes a nucleus persists, as shown below/13.
Nuclei of non-hematologic cells tend to be a bit more regular, though the shape/proportion still vary widely. For example, spindle-shaped nuclei characterize muscles and fibroblasts, and finding such nuclei is important in pathology of related tumors./14
And the nuclei of spermatozoa are all sorts of crazy shapes, for reasons that may have to do with efficient swimming. (Image: Jesús L Yániz et al Asian Journal of Andrology, 2016)/15
These patterns change in disease. In B12 and folate deficiency, and sometimes iron deficiency, a high proportion of neutrophils will develop extra lobes in the nucleus. The mechanism is unclear – “impaired DNA synthesis” is usually cited, but that’s kind of hand-waving.../16
The "rule of 5s" states: if >5% of neutrophils have 5 lobes, or if any have 6 or 7 lobes, that's abnormal. BTW there’s a rare hereditary spinocerebellar ataxia+ syndrome, Boucher-Neuhäuser syndrome, caused by germline PNPLA6 mutations, in which neutrophils are hypersegmented./17
The opposite type of lobation defect may happen in myelodysplastic syndromes #MDS: a megakaryocyte might have just a single-lobed nucleus like the ones below at left, or just 2 lobes, while MDS neutrophils may only have 2 lobes (aka acquired or pseudo-Pelger–Huët anomaly)./18
Why are normal neutrophils multilobed? It's not entirely clear. Drs. Veda from Bangalore and Manley et al from @MonashUni summarize the unknowns well. Perhaps it is to enable their “crawling” function… but monocytes are also very flexible, and they are not as highly lobated./19
One potential explanation is that neutrophils also generate neutrophil extracellular traps (NETs): chromatin “nets” released from nucleoplasm to extracellular space, which have antibacterial effects. Lobation facilitates NETosis (image from @nature). But we really don't know./20
Underlying the nuclear membrane is the nuclear lamina, a mesh-like structure comprised of intermediate filaments called lamins (A, B and C). Lamins are tethered to the inner nuclear membrane. The lamins provide mechanical support & influence nuclear size and shape./21
Lamin B receptors (LBR) are especially important in determining morphology. Reduced LBR causes neutrophil nuclei to become hypolobated, as in Pelger-Huët anomaly, which results from a germline defect in lamins and about which I did an early Tweetstory:/22
In megaloblastic/megaloblastoid maturation, there is nuclear-cytoplasmic asynchrony with chromatin in the nucleus more “open” (non-condensed) than it should be for the degree of cell maturation. In addition to B12/folate, one sees this w/ MDS & antimetabolites, eg MTX or Hydrea.
The congenital dyserythropoietic anemias (CDA) can have some really bizarre nuclear morphology. In CDA type 1 there is characteristic “nuclear bridging” from one red cell precursor to the next – as if the two sibling cells are unwilling to let go./24
Well, Twitter only allows 25 tweets at a time, but there's more fun to come in this thread - we've shown lots of histopathology images, and we have yet to mention food!😜 But we will - and we'll also discuss nuclear substructures. The rest is coming within the hour, D.V./25
The Barr body, named after Murray Barr of Western Ontario (1908 – 1995), resembles a drumstick . It is a condensed X chromosome found in XX females. No one knows why the extra X does this and doesn’t just sit condensed inside a lobe. (BTW: Barr also invented the buccal swab!)/26
The Reed-Sternberg cell, first discovered by Dorothy Reed at @HopkinsMedicine in 1901 and later by Austrian pathologist Carl Sternberg, is diagnostic of Hodgkin lymphoma. Their nuclei are often compared to owl eyes, but some people think we should call them “emoji eyes”🙄./27
Did you know owls don’t have eye "balls"? Owl eyes are more cone or rod shaped, fittingly, given that cones and rods describe retinal cells and owls have amazing vision. But their retina does not have cone cells so they see black and white... /28
The “Orphan Annie Eye” nucleus is characteristic of papillary carcinoma of the thyroid. It is was named by Dr Nancy Warner @USC in 1971 after a comic strip that ran from 1924 to 2010. Histology image is from PathologyStudent.com. We don't know why the nuclei do this./29
“Marty Feldman cells” were named in the 1970s after actor Feldman of Young Frankenstein fame, with his characteristic misaligned eyes. These are megakaryocytes with 2 widely-spaced nuclei, sometimes seen in MDS. /30
I also did a #HematologyTweetstory on “Pawn Ball nuclei” last year. These are characteristic of MDS also, but with 3 lobes instead of 2 like Marty Feldman cells. /31
In addition to Orphan Annie nuclei, thyroid cancer cells can have a hazy “ground glass” nucleus. Ground glass most commonly used to describe an infiltrate pattern in the lung, which can indicate a range of pathologies – infections and inflammatory conditions.../32
What is “ground” glass, anyway? It is nothing special -- just regular glass in which the surface has been ground to produce a matte finish. You’ll find it in any chemistry lab, like on this bottle stopper from the Science Company./33
Back to nuclei. There are some tumors in which the nucleus is dense & disproportionate. These are the so-called “small round blue cell tumors” – Ewing sarcoma and some other sarcomas, neuroblastoma, medulloblastoma, retinoblastoma, Wilms tumor, small cell cancer and so on./34
I wet your appetite above with the drumstick Barr body... Now let's do some more "eating." Pathologists love their food metaphors. A terrific list of dozens of food eponyms was compiled in 2017 by Vimal and Nishanthi in Puducherry, India:/35 ncbi.nlm.nih.gov/pmc/articles/P…
One food metaphor relevant to our discussion is “coffee bean nucleus”, classically seen in Brenner tumor of the ovary, or granulosa tumors but sometimes seen in Langerhans (!) histiocytosis or thyroid cancer. This Brenner tumor image is from Borah et al, J Midlife Health 2011./36
Another food nucleus is the “raisin nucleus”, with coarse chromatin and a wrinkled nuclear membrane. It's a stretch, I know. I heard through the grapevine 😜 that raisin nuclei can be seen in many different poorly differentiated carcinomas. Image is from the AUA./37
Linking nuclei types: JJ Thomson's “raisin bun” or “plum pudding” model of the atomic nucleus was what Ernest Rutherford disproved in 1911 with his scattering experimeents)/38
And the “fried egg” of hairy cell leukemia, where the round nuclei are the yolk. It is not a very specific pattern; there are other malignancies where the nucleus resembles a yolk in an egg./39
OK enough food. Nucleli blow up in various ways. In addition to apoptosis, there is karyorrhexis from Greek κάρυον, "kernel, seed or nucleus" & ῥῆξις "bursting”, pyknosis (from Greek word πυκνός "to thicken up, to condense", and karyolysis where the nucleus just dissolves./40
Benjamin Skinner and Emma Johnson @Cambridge_Uni wrote a long review of nuclear morphologies in Chromosoma in 2017 which describes the links between structure and function. This lovely figure is from their paper./41
Nuclear shape, polarity, and position within the cell is a really dynamic process, depending on the activity level of transcription and numerous other factors. There are numerous substructures – the largest by far is the nucleolus, where ribosome biogenesis happens.
Once one ventures beyond traditional light microscopy, using electron microscopy and fluorescent probes, there are all sorts of weird and wonderful nuclear substructures. This gorgeous image is by David Spector @CSHL from Journal of Cell Science in 2001./42
One well-studied type of nuclear substructure is the “PML body”, so-called because they are abnormally dispersed in clonal cells from patients with acute promyelocytic leukaemia (APML). They have an important normal transcriptional role./43
There are usually 5-30 PML nuclear bodies in mammalian cell nuclei; they range from 0.2-1 μm in diameter. This figure, from Luciani et ai 2006, shows ATRX (which I spent 2 years working on in the Higgs and Gibbons groups @MRC_WIMM) and other proteins co-localize in PML bodies./44
The nucleus also has 1-10 "Cajal bodies", also called coiled bodies, similar size to PML bodies. They look like tangled thread under EM. They’re important in RNA processing, too. This image is from the Neugebauer lab @Yale. Named after Spanish anatomist Santiago Ramón y Cajal/45
Cajal bodies also come in pairs, called “gems” or “Gemini of Cajal bodies”. Not entirely clear what gems do, but they don’t have coilin and the do have SMN (survival of motor neuron) protein, neither of which is true of single Cajal bodies./46
Then there is the “polymorphic interphase karyosomal association” (PIKA) first described in 1991 @hopkinsmedicine by the Earnshaw lab…/47
And “splicing speckles”, aka snurposomes, are dynamic structures enriched in pre-mRNA splicing factors. On EM, they look like interchromatin granules. “Paraspeckles” are found next to speckles. I think it is safe to say we’ve only just begun to understand the nucleus./48
So that's a whirlwind tour through the cell nucleus: a bit of history (not so much this time, only a few B&W photos), normal & pathologic morphology, pathologist creativity in nuclear description, owls, and the new world of the nuclear substructure. Hope you enjoyed it.🙂/49
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