Changes in the expression of α-fodrin during embryonic development of Xenopus laevis

Abstract

Fodrin (nonerythroid spectrin) and its associated proteins have been previously implicated in the establishment of specialized membrane-cytoskeletal domains in differentiating cells. Using antiserum which is monospecific for the α-subunit of fodrin, we demonstrate that α-fodrin is present in oocytes and adult tissues of Xenopus laevis. Analyses of the de novo synthesis of α-fordin during embryonic development reveal that α-fodrin is synthesized in oocytes, but not during early development. To investigate the level of control of α-fodrin expression, we isolated two cDNA clones for oocyte α-fodrin. The oocyte cDNA clones were identified as encoding portions of α-fodrin based on DNA sequence analysis and on the comparison of the predicted amino acid sequence of the cDNAs with the known sequence of human erythrocyte α-spectrin. The Xenopus α-fodrin cDNAs hybridize to a transcript of ~9 kb on RNA blots, and probably to a single gene type on genomic DNA blots. Both RNA blot analyses and S1 nuclease protection assays with the Xenopus α-fodrin cDNAs demonstrate that the observed decline in the de novo synthesis of α-fodrin polypeptides is controlled by a dramatic decrease in the abundance of α-fodrin transcripts after fertilization. In contrast, levels of actin transcripts do not decrease during this period. Inasmuch as steady-state levels of α-fondrin transcripts rise by tne neurula stage of development, these results suggest that the synthesis of α-fodrin polypeptides during embryonic development of Xenopus is regulated, rather than constitutive, and that the primary level of control is the steady-state abundance of mRNA.