Submitted December 11, 2007
Returned for revision January 10, 2008
Accepted April 4, 2008
Testis
Expression Patterns of SP1 and SP3 During Mouse Spermatogenesis: SP1 Down-Regulation Correlates with Two Successive Promoter Changes and Translationally Compromised Transcripts
Wenli Ma ,
Gary C. Horvath ,
Malathi K . Kistler ,
and
W. Stephen Kistler *
* To whom correspondence should be addressed. E-mail: kistler{at}mail.chem.sc.edu.
Abstract
Because of their prominent roles in regulation of gene expression, it is important to understand how levels of Krüpple-like transcription factors SP1 and SP3 change in germ cells during spermatogenesis. Using immunological techniques we found that both factors decreased sharply during meiosis. SP3 declined during the leptotene to pachytene transition while SP1 fell somewhat later, as spermatocytes progressed beyond early pachytene. SP3 reappeared for a period in round spermatids. For Sp1 it is known that the transition to pachytene is accompanied by loss of the normal 8.2 kb mRNA and appearance of a prevalent 8.8 kb variant, which has not been well characterized. We have now shown that this pachytene-specific transcript contains a long, unspliced sequence from the first intron and that this sequence inhibits expression of a reporter, probably due to its many short open reading frames. A second testis-specific Sp1 transcript in spermatids of 2.4 kb has also been reported previously. Like the 8.8 kb variant, it is also translationally compromised. We have confirmed by Northern blotting that the 8.8, 8.2 and 2.4 kb variants account for the major testis Sp1 transcripts. Thus the unexpected decline of SP1 protein in the face of continuing Sp1 transcription is explained in large part by poor translation of both novel testis transcripts. As part of this work we also identified five additional minor Sp1 cap sites by 5' RACE, including a trans-spliced RNA originating from the Glcci1 gene.
Key words:
Testis •
Meiosis •
Spermatogenesis •
alternate promoter •
alternative splicing
