The Ca2+-binding protein parvalbumin: molecular cloning and developmental regulation of mRNA abundance.

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Abstract
Parvalbumin (PV) is a Ca2+-binding protein found only in vertebrates. It is postulated to serve as a soluble relaxing factor in fast mammalian muscle. A rat PV C [complementary]DNA clone was isolated and used as a probe to examine changes in PV mRNA during muscle and brain development. a cDNA library was contructed in PUC8/PUC9 plasmid vectors from adult poly(A)+ RNA isolated from rat gastrocnemius muscle. The library was screened with a 17-meroligonucleotide encoding amino acids 28-33 of rat PV. One recombinant (9f) was confirmed as a PV clone by DNA sequencing and was shown to contain 73% of the protein coding sequence. Hybridization of clone 9f to RNA separated by electrophoresis revealed 2 species 700 and 1100 nucleotides long but genomic blotting indicates that PV may be a single copy gene. Highest levels of PV mRNA are found in the gastrocnemius, which is a fast contracting/relaxing muscle. Skin contains the next highest amount of PV mRNA followed, in order, by brain and the slow twitch soleus muslce. Rat muscle PV mRNA levels increase 15-20-fold between postnatal days 4 and 20 as measured by dot blot hybridization of total RNA, whereas only a slight increase was observed when young and adults brains were compared. The changes in PV mRNA during development appears to be selective, because mRNA coding for the structurally homologous Ca2+-binding protein calmodulin (CaM) was found to change only slightly in muscle. CaM mRNA levels decrease during the early days of brain ontogeny. The mRNA that encode the homologous Ca2+-binding proteins PV and CaM appear to be developmentally regulated in a tissue-specific manner.