Developmental expression of poly(A) binding protein mRNAs during spermatogenesis in the mouse

Abstract

The poly(A) binding protein (PABP), a conserved protein that binds to the 3' poly(A) tail on mRNAs in eukaryotic cells, has been implicated in the regulation of mRNA stability and translation. Two PABP cDNAs with different sequences were isolated from mouse testis cDNA libraries. The predicted amino acid sequence of one, PABP1, is nearly identical (98.9%) to human liver PABP, while 80% of the amino acids of the second, PABPt, are identical to mouse and human PABPs. Northern blots reveal that there is one major PABP mRNA species in liver, muscle, kidney, and brain, two in spleen, and at least four in testis. The levels of PABP mRNA in testis are 5-10-fold higher than in these somatic tissues, but surprisingly the vast majority of all PABP mRNA size variants sediment more slowly than single ribosomes, indicating strong translational repression. Reverse transcriptase-polymerase chain reaction assays demonstrate that PABPt mRNAs are abundant only in testis. Northern blots of RNAs purified from highly enriched spermatogenic cells show that the high levels, multiple sizes of PABP mRNAs, and the PABPt mRNA are present in meiotic and early haploid spermatogenic cells, and are sharply reduced in late haploid cells. Comparison of the binding of PABP1 and PABPt to poly(A) Sepharose in vitro revealed subtle differences, even though PABPt contains substitutions for highly conserved aromatic amino acids that are thought to be necessary for binding to poly(A). The existence of two PABP isoforms in mouse spermatogenic cells could influence cytoplasmic gene expression during spermatogenesis.

The poly(A)-binding protein genes, EPAB, PABPC1, and PABPC3 are differentially expressed in infertile men with non-obstructive azoospermia

“…Hence, use of pathologic testicular samples may lead to changes in spatial and temporal expression patterns of the PABPC1 and PABPC3 genes; therefore, new studies are required for these genes on testicular samples obtained from healthy and fertile men. Notably, the expression levels of the Pabpc1 and Pabpc2 (known as PABPC3 in human) genes in the mouse spermatogenic cells were found to be compatible with our findings [22].…”

“…Taken together, spatial and temporal expression patterns of the EPAB, PABPC1, and PABPC3 genes have been characterized in mouse [21,22,26,28] and human [24,27] spermatogenic cells. Based on the expressional distributions of the PABP genes, they appear to play roles in the posttranscriptional control and regulation of the translation activities of the mRNAs, being required for proper spermatogenic activity.…”

“…When their translation is required during late stages of spermatogenesis, the long poly(A)-tails of target mRNAs are shortened to approximately 30 nucleotides to trigger their association with ribosomes for translation [14,16]. In vertebrates, the post-transcriptional or translational control of these mRNAs in germ cells and early embryos are mainly performed by cognate poly(A)-binding proteins, EPAB [17][18][19][20], PABPC1 [20][21][22][23], and PABPC3 [21,22,24] via binding their poly(A) tails.…”

“…The poly(A)-binding protein, cytoplasmic 1 (PABPC1, also known as PABP1) defined as a somatic poly(A)-binding protein is generally expressed in mouse [25,26] and human [27,30] gonads. On the other hand, the poly(A)-binding protein, cytoplasmic 3 (PABPC3; also known as tPABP, and PABPC2 in mouse) is synthesized only in spermatocytes and round spermatids in mouse [21,22], but only in round spermatids in human testis [24]. The central function of the PABP proteins seems to govern translational control and stabilization of the mRNAs in the spermatogenic cells throughout spermatogenesis.…”

Diesel exhaust particles disturb gene expression in mouse testis

“…1(B)]. Among the exposure reactions of all the clones named above, only the induction of R35 (USP52; poly (A)-specific ribonuclease subunit 2 (Uchida et al, 2004)) and the suppression of R60 (testis specific poly A binding protein 2 (Kleene et al, 1994)) suggested that DEP exposure stimulated the degradation of mRNA in testis. Furthermore, the downregulation of R39, which is similar to the testis-specific Dnaj-homolog and acts as a cochaperone with heat-shock protein 70 in the coexpressing cell line (Farinha et al, 2002), indicated that the stability of some proteins in testis might decline.…”