Cyclical alternative exon splicing of transcription factor cyclic adenosine monophosphate response element-binding protein (CREB) messenger ribonucleic acid during rat spermatogenesis.
During spermatogenesis, the levels of cAMP in seminiferous tubules undergo stage-dependent cyclical fluctuations. We show that changes in cAMP levels are accompanied by alternative exon splicing of the RNA encoding the cAMP-responsive transcription factor CREB (cAMP response element-binding protein), expressed in both the Sertoli and germ cells. Exons Y and W are expressed exclusively in the testis, and they introduce stop codons into the normal protein coding frame of CREB. The splicing in of W was shown earlier to activate the internal translation of two alternative products of the CREB messenger RNA (mRNA) containing the DNA-binding domain (I-CREBs). The I-CREBs act as potent inhibitors of activator isoforms of CREB. The functions of the alternatively spliced exon Y are unknown. To investigate whether the splicing of exons W and Y is regulated during spermatogenesis, seminiferous tubules, isolated from adult rats, were dissected into segments representing different stages of the spermatogenic cycle and were analyzed by RT-PCR. The analyses of pooled-tubule segments revealed stage-dependent splicing of both exons W and Y in the CREB transcripts. Single tubules were dissected into smaller segments for greater staging accuracy and were analyzed by RT-PCR for CREB mRNAs containing either exons W or Y, as well as for FSH receptor mRNA. This analysis confirmed that a marked, cycle-dependent variation in CREB mRNA levels was occurring. Maximal splicing of exons W and Y occurs independently at different stages of the spermatogenic cycle, stages II-VI and IX, respectively. The distinct spermatogenic cycle-dependent regulation of the splicing of exons W and Y provides further evidence in support of a functional relevance for CREB-W and Y mRNA isoforms in spermatogenesis.
Daniel
P B
PB
Laboratory of Molecular Endocrinology, Massachusetts General Hospital and Howard Hughes Medical Institute, Harvard Medical School, Boston 02114, USA.
Habener
J F
JF
D017398:Alternative Splicing; D000818:Animals; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics*; D005091:Exons / Q000235:genetics*; D014644:Genetic Variation / Q000235:genetics; D008297:Male; D010507:Periodicity; D012333:RNA, Messenger / Q000235:genetics*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013091:Spermatogenesis / Q000502:physiology*; D013997:Time Factors
D017362:Cyclic AMP Response Element-Binding Protein; D012333:RNA, Messenger