Do RBC"S also require any companion cells, like sieve tubes require due to absence of nucleus?

Mature red blood cells do not contain nucleus. RBC's perform the function of transportation of oxygen through blood and they have to squeeze through various tiny blood vessels inside the body. Presence of nucleus is not required for this function, instead it inhibits this function as nucleus occupies a large space in cells. So, RBC's loose the nucleus to utilize maximum space for oxygen. 

RBC's don't replicate and have a life span of around 120 days. Initially they have nucleus but as they mature, they loose it.  So, without nucleus they can survive for around 120 days as they make all the required proteins and materials during the initial stages of life when they have nucleus.   

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