Genomic structure and cloning of two transcript isoforms of human Sp8.
BACKGROUND
The Specificity proteins (Sp) are a family of transcription factors that have three highly conserved zinc-fingers located towards the carboxy-terminal that bind GC-boxes and assist in the initiation of gene transcription. Human Sp1-7 genes have been characterized. Recently, the phenotype of Sp8 null mice has been described, being tailless and having severe truncation of both fore and hind limbs. They also have malformed brains with defective closure of the anterior and posterior neuropore during brain development.


RESULTS
The human Sp8 gene is a three-exon gene that maps to 7p21.3, close to the related Sp4 gene. From an osteosarcoma cell line we cloned two transcript variants that use two different first exons and have a common second exon. One clone encodes a 508-residue protein, Sp8L (isoform 1) and the other a shorter 490-residue protein, Sp8S (isoform 2). These two isoforms are conserved being found also in mice and zebrafish. Analysis of the Sp8L protein sequence reveals an amino-terminal hydrophobic Sp-motif that is disrupted in Sp8S, a buttonhead box and three C2H2 zinc-fingers. Sp8 mRNA expression was detected in a wide range of tissues at a low level, with the highest levels being found in brain. Treatment of the murine pluripotent cell line C3H10T1/2 with 100 ng/mL BMP-2 induced Sp8 mRNA after 24 hours.


CONCLUSIONS
There is conservation of the two Sp8 protein isoforms between primates, rodents and fish, suggesting that the isoforms have differing roles in gene regulation. Sp8 may play a role in chondrogenic/osteoblastic differentiation in addition to its role in brain and limb development.
Milona
Maria-athina
MA
Department of Cell Biology and Genetics, Faculty of Medicine, Erasmus Medical Center Rotterdam, PO Box 1738, 3000 DR Rotterdam, The Netherlands. m.mylona@erasmusmc.nl <m.mylona@erasmusmc.nl>
Gough
Julie E
JE
Edgar
Alasdair J
AJ
D000595:Amino Acid Sequence / Q000235:genetics; D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000502:physiology; D002460:Cell Line; D045744:Cell Line, Tumor; D002874:Chromosome Mapping / Q000379:methods; D002897:Chromosomes, Human, Pair 7 / Q000235:genetics; D003001:Cloning, Molecular / Q000379:methods*; D017124:Conserved Sequence / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D005091:Exons; D005786:Gene Expression Regulation / Q000235:genetics / Q000502:physiology; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D051379:Mice; D008809:Mice, Inbred C3H; D008969:Molecular Sequence Data; D009928:Organ Specificity / Q000235:genetics; D010006:Osteoblasts / Q000737:chemistry / Q000378:metabolism; D012516:Osteosarcoma / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics; D014157:Transcription Factors / Q000737:chemistry* / Q000235:genetics* / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000502:physiology; D029961:Zebrafish Proteins / Q000737:chemistry; D016335:Zinc Fingers / Q000235:genetics
D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D029961:Zebrafish Proteins; C525718:BMP2 protein, human; C525719:Bmp2 protein, mouse; C501901:SP8 protein, human