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Mer belongs to the Tyro 3 family of receptor tyrosine kinases (RTKs). Together with Axl and Rse, the three RTKs are believed to play important functional roles in the male gonads because gene knockout male mice lacking all of these receptors are infertile. In the present study, postnatal expression of Axl and Rse in mouse testes decreased during maturation while expression of Mer increased age-dependently during testicular development. | Eur. J. Biochem. 269 3789-3800 2002 FEBS 2002 doi 10.1046 j.1432-1033.2002.03092.x The proximal ós-acting elements Sp1 Sp3 and E2F regulate mouse mer gene transcription in Sertoli cells Connie C. S. Wong and Will M. Lee Department of Zoology The University of Hong Kong China Mer belongs to the Tyro 3 family of receptor tyrosine kinases RTKs . Together with Axl and Rse the three RTKs are believed to play important functional roles in the male gonads because gene knockout male mice lacking all of these receptors are infertile. In the present study postnatal expression of Axl and Rse in mouse testes decreased during maturation while expression of Mer increased age-dependently during testicular development. To investigate the transcriptional regulation of gene expression in the testis a w 1.5 kb fragment of the 5 flanking sequence of Mer was isolated. The sequence lacks a typical TATA or CAAT box. 5 RACE revealed that the putative major transcriptional start site of Mer is located at 102 bp upstream of the translation initiation site. Using transient transfections of luciferase reporter constructs driven by various lengths of the 5 flanking sequence the gene segment -321 126 showed the highest transcriptional activity in a mouse Sertoli cell line TM4 . DNAase I footprinting experiments revealed four footprints within the region from -321 to -26 including three binding sites for the transcriptional factor Specificity protein 1 Sp1 and one for an unknown transcriptional factor. Electrophoretic mobility shift assay EMSA supershift assay mutation studies and cotransfection demonstrated that those Sp1 cis-acting motifs interacted either with Sp1 or Sp1 Sp3 depending on location and the nearby nucleotide sequences. An E2F binding site which down-regulates Mer transcription as revealed by EMSA deletion and mutation studies was identified downstream in the proximity of the promoter. Taking all of these data together the study has demonstrated that Sp1 Sp3 E2F and probably .
