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ae-3803, macrophage, and erythroblast (hataraku saibou) drawn by hikari_niji

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    Erythroblast and Ms. Macrophage~

    my Illustration of Young Red Blood Cell with her Teacher Ms. Macrophage~
    from Hataraku Saibou

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    PraiseVectron
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    Macrophage onee-san has three purposes as a nurse cell. She provides nourishment to the developing red blood cell. She cleans up the nucleus (red hat fuzz) that is lost as the red blood cell matures. She also exterminates defective red blood cells, and those that fail to mature properly.

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    Rathurue
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    PraiseVectron said:

    Macrophage onee-san has three purposes as a nurse cell. She provides nourishment to the developing red blood cell. She cleans up the nucleus (red hat fuzz) that is lost as the red blood cell matures. She also exterminates defective red blood cells, and those that fail to mature properly.

    It was not 'lost', but rather 'ejected' by the Erythrocyte itself out, of which Macrophage will eat it. In the manga it was depicted as Macrophage tore the puffy ball from the cap, making it looks like the adult RBC outfit cap (and it's probably was).

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    NNescio
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    Rathurue said:

    It was not 'lost', but rather 'ejected' by the Erythrocyte itself out, of which Macrophage will eat it. In the manga it was depicted as Macrophage tore the puffy ball from the cap, making it looks like the adult RBC outfit cap (and it's probably was).

    So, Macrophage onee-san noms on baby red blood cell brains?

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    NNescio
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    Garrus said:

    That's a mammal thing as I recall. At the very least, avian RBCs do retain their nuclei.

    Most (if not all) other vertebrates as well. Enucleated RBCs are mostly (if not exclusively) a mammalian adaptation. IIRC the theory is that mammals evolved during the low-oxygen Triassic period and had less advanced pulmonary/circulatory systems compared to the more 'advanced' reptiles and birds (the archosaurs), so they needed some sort of leg-up.

    (Later on we kept that evolutionary advantage... more like a trade-off, really, but like spaghetti programming, once you introduce a feature it becomes very hard to remove it because of all the dependencies.)

    That said, enucleated RBCs have sometimes been detected (as a small fraction of overall RBCs) in the blood of birds and reptiles before (and amphibians too, IIRC), but's that's considered unusual (like nucleated RBCs in mammals).

    Updated by NNescio

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    Rathurue
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    NNescio said:

    Most (if not all) other vertebrates as well. Enucleated RBCs are mostly (if not exclusively) a mammalian adaptation. IIRC the theory is that mammals evolved during the low-oxygen Triassic period and had less advanced pulmonary/circulatory systems compared to the more 'advanced' reptiles and birds (the archosaurs), so they needed some sort of leg-up.

    (Later on we kept that evolutionary advantage... more like a trade-off, really, but like spaghetti programming, once you introduce a feature it becomes very hard to remove it because of all the dependencies.)

    That said, enucleated RBCs have sometimes been detected (as a small fraction of overall RBCs) in the blood of birds and reptiles before (and amphibians too, IIRC), but's that's considered unusual (like nucleated RBCs in mammals).

    Actually, mammalian RBCs evolved to be without nucleus so they can be more pliable and carry more oxygen molecules, thus can carry more oxygen per unit while passing small capillaries without being stuck.

    Without nucleus, they also avoid breaking from oxidative damage, like a normal cell would because there's no waste product accumulated in them.

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    NNescio
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    (Disclaimer: I am no biologist.)

    Rathurue said:

    Actually, mammalian RBCs evolved to be without nucleus so they can be more pliable and carry more oxygen molecules, thus can carry more oxygen per unit while passing small capillaries without being stuck.

    That's the 'leg-up' I alluded to. I was providing an explanation why the evolutionary pressure was present in early mammals but not in archosaurs (better lungs, wider capillaries).

    It's also a trade-off of sorts, as enucleated RBCs cannot undergo mitosis, complicating homeostasis especially under osmotic stress (technically most mature end-stage nucleated RBCs also cannot [the nucleus becomes deactivated], but the penultimate-stage RBCs can, and they generally can be found circulating in the blood and can be mobilized very quickly in the event of blood loss).

    Most of the vetebrates with nucleated RBCs also tend to have smaller genomic sizes (and smaller nuclei) compared to mammals of equivalent size (birds in particular have very small genome sizes, about 1-2 Gb), so the presence of a nucleus doesn't affect cell pliablity as much. Birds and most other ectothermic vetebrates also have wider capillaries compared to mammals.

    Curiously enough, some salamanders have also evolved high levels of enucleated RBCs. They also happen to have large genomic sizes and small capillaries (and bodies), putting them in a somewhat similar situation as the early mammals (and pre-mammal synapsids).

    Rathurue said:

    Without nucleus, they also avoid breaking from oxidative damage, like a normal cell would because there's no waste product accumulated in them.

    That's the prevailing theory (the mitochondrial stress hypothesis), but some research have indicated this to not be true at least for some birds.

    Ultimately, however, what works for mammals may not work for other vetebrates, and vice versa. A viable adapation for one may not necessarily be viable for another, especially considering their morphological, behavioural and enviromental differences.

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