Sequence characterization of a newly identified human alpha-tubulin gene (TUBA2)

A role for E2F6 in the restriction of male-germ-cell-specific gene expression

E2F transcription factors play a pivotal role in the regulation of cellular proliferation and can be subdivided into activating and repressing family members [1]. Like other E2Fs, E2F6 binds to E2F consensus sites, but in contrast to E2F1-5, it lacks an Rb binding domain and functions as an Rb-independent transcriptional repressor [2, 3, 4 and 5]. Instead, E2F6 has been shown to complex with Polycomb (PcG) group proteins [6 and 7], which have a well-established role in gene silencing. Here, we show that E2F6 plays an unexpected and essential role in the tissue specificity of gene expression. E2F6-deficient mice ubiquitously express the alpha-tubulin 3 and 7 genes, which are expressed strictly testis-specifically in control mice. Like an additional E2F6 target gene, Tex12, that we identified, tubulin 3 and 7 are normally expressed in male germ cells only. The promoters of the alpha-tubulin and Tex12 genes share a perfectly conserved E2F site, which E2F6 binds to. Mechanistically, E2F6-mediated repression involves CpG hypermethylation locking target promoters in an inactive state. Thus, E2F6 is essential for the long-term somatic silencing of certain male-germ-cell-specific genes, but it is dispensable for cell-cycle regulation.

Kabuki syndrome: Clinical data in 20 patients, literature review, and further guidelines for preventive management

The Kabuki syndrome, or Niikawa-Kuroki syndrome, is a clinically recognizable syndrome of unknown etiology. Clinical findings include early hypotonia, joint laxity, developmental delay, facial dysmorphism, persistent fetal fingertip pads, cleft palate, hypodontia, lip nodules, heart defects, and a variety of other structural defects. Behavior in general is social and pleasant. In collaboration with the Dutch Kabuki Network, we evaluated the medical data of 20 individuals diagnosed with the syndrome and compared them with data from the literature. In our literature review we used convincing cases only. Frequent findings in the oral region are under-reported in the literature: apart from the cleft palate (in about 50%), hypodontia with predominantly absence of the upper lateral incisors, and a full lower lip with symmetrical nodules, or (in a minority) lip-pits are frequent findings. Also under-reported is the presence of a thickened nuchal fold during pregnancy and hydrops in the neonatal period. Clinical recognition in the neonate is difficult. Towards early puberty acute and serious weight excess has been experienced. We suggest that a cytogenetic abnormality should be ruled out in all cases. We provide further guidelines for preventive management.

TUBA8: A new tissue-specific isoform of alpha-tubulin that is highly conserved in human and mouse

We have cloned and sequenced a cDNA from a human adult skeletal muscle cDNA library, encoding for a novel isoform of alpha-tubulin (tuba8) that is preferentially expressed in heart, skeletal muscle, and testis. A genomic DNA sequence from the chromosomal region 22q11 allowed us to determine the complete structure of the TUBA8 gene that mirrors the canonical exon/intron organization of the vertebrate alpha-tubulin genes. We also cloned and sequenced the cDNA of its murine homologue (MMU-TUBA8). The latter encodes for a protein that differs from its human counterpart in only three amino acids, revealing an extreme rate of conservation that is even extended to both the 3' and 5' UTRs of the mRNAs. Sequence comparison of these novel isoforms with other known alpha tubulins shows that tuba8 is the most divergent member of the mammalian alpha-tubulin family. The sequence peculiarity of the human and murine tuba8 strongly suggests that they might have functional significance and, according to the multi-tubulin hypothesis, that they might play specific functional roles in the cell cytoskeleton.