Patterns of spectrin transcripts in erythroid and non‐erythroid cells

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Abstract
Spectrin is the major protein of the membrane erythrocyte skeleton. More recently, homologous but non‐identical spectrins (fodrins) were also found in various non‐erythroid tissues. Spectrin mRNA in erythroid and various non‐erythroid cells was examined by direct hybridization with human α‐spectrin, β‐spectrin (erythroid spectrins), and α‐fodrin (non‐erythroid spectrin) cDNA probes. Northern blot analysis of poly (A)+ RNA revealed a distinct pattern of expression in erythroid vs. non‐erythroid cells. Erythroid cells from early erythroblasts to reticulocyte stage expressed two mRNA species of β‐spectrin, whereas they expressed only a single speeies of α‐spectrin, and no α‐fodrin mRNA. In contrast, non‐erythroid cells (platelets, myeloid cells, liver, muscle, heart, cerebellum, and eye lens) expressed either no α‐spectrin mRNA or a different molecular weight transcript(s) of this gene, and a single species of β‐fodrin mRNA. Additionally, they also expressed from none to multiple species of β‐spectrin, and these were of different molecular size(s) from that found in erythroid cells (with the exception of platelets). Transcripts of non‐erythroid spectrin, α‐fodrin, were found as a single copy only in non‐erythroid tissues. Human and murine erythroleukemia cells expressed both erythroid spectrin transcripts in addition to α‐fodrin and raise the possibility that erythroid progenitors may have the potential to express both erythroid and non‐erythroid species. These data indicated that several mRNA species of β‐spectrin could be detected in both erythroid and some non‐erythroid cells. Whether multiple spectrin peptides could also be found with functional heterogneity is unclear. However, in each case, the pattern combination observed appeared to be tissue‐specific.