TBX3, the gene mutated in ulnar-mammary syndrome, promotes growth of mammary epithelial cells via repression of p19ARF, independently of p53.

TBX3, the gene mutated in ulnar-mammary syndrome (UMS), is involved in the production of a transcription factor of the T-box family, known to inhibit transcription from the p14ARF (p19ARF in mouse) promoter in fibroblasts and to contribute to cell immortalization. One of the main features of the UMS phenotype is the severe hypoplasia of the breast, associated with haploinsufficiency of the TBX3 gene product. In mice homozygous for the targeted disruption of Tbx3, the mammary glands (MGs) are nearly absent from early stages of embryogenesis, whereas in heterozygous adults, the MGs show reduced ductal branching. All these data strongly suggest a specific role of TBX3 in promoting the growth of mammary epithelial cells (MECs), although direct evidence of this is lacking. Here, we provide data showing the growth-promoting function of Tbx3 in several models of MECs, in association with its ability to repress the ARF promoter. However, no effect of Tbx3 on cell differentiation or apoptosis has been observed. The growth promoting function also entails the down-regulation of p21 ( CIP1/WAF ) and an increase in cyclin D1 but is independent of p53 and Mdm2 cell-cycle regulatory proteins, as p53-null MECs show similar growth responses associated with the up- or down-regulation of Tbx3. This is the first direct evidence that the level of Tbx3 expression positively controls the proliferation of MECs via pathways alternative to Mdm2-p53.

Novel TBX3 mutation data in families with ulnar-mammary syndrome indicate a genotype-phenotype relationship: mutations that do not disrupt the T-domain are associated with less severe limb defects.

We describe a family affected by Ulnar-Mammary syndrome (UMS) in which typical UMS traits (hypoplasia of the breast and axillary hair, upper limbs and genital defects) are present together with cardiac malformations and pulmonary stenosis. Sequence analysis of TBX3 shows a new heterozygous mutation that causes a frame-shift (Nt.1586-1587-insC) in exon 6, resulting in a truncated ORF. Recently the expression of Tbx3 has been described also in the septal region of the embryonic murine heart. This observation may establish a link between the congenital heart defects and the TBX3 mutation in this family. Combining the TBX3 mutation data in the literature with this novel mutation we find an association between mutations that disrupt the DNA-binding domain and a higher frequency of severe upper limb malformations and teeth defects. A possible explanation is that mutant TBX3 proteins that retain the T-domain, if translated, might be minimally active in promoting/repressing transcription of target genes in the limbs and in other embryonic tissues.

The Dlx5 homeodomain gene is essential for olfactory development and connectivity in the mouse.

The distalless-related homeogene Dlx5 is expressed in the olfactory placodes and derived tissues and in the anterior-basal forebrain. We investigated the role of Dlx5 in olfactory development. In Dlx5(-/-) mice, the olfactory bulbs (OBs) lack glomeruli, exhibit disorganized cellular layers, and show reduced numbers of TH- and GAD67-positive neurons. The olfactory epithelium in Dlx5(-/-) mice is composed of olfactory receptor neurons (ORNs) that appear identical to wild-type ORNs, but their axons fail to contact the OBs. We transplanted Dlx5(-/-) OBs into a wild-type newborn mouse; wild-type ORN axons enter the mutant OB and form glomeruli, but cannot rescue the lamination defect or the expression of TH and GAD67. Thus, the absence of Dlx5 in the OB does not per se prevent ORN axon ingrowth. In conclusion, Dlx5 plays major roles in the connectivity of ORN axons and in the differentiation of OB interneurons.

Characterisation and expression analysis of the WDR9 gene, located in the Down critical region-2 of the human chromosome 21.

We report the isolation and characterisation of the gene WDR9 (WD Repeat 9), located in the Down Syndrome critical region-2 (DCR-2) from the human chromosome 21. This gene spans 125 kb of genomic sequence and is organised in 41 exons and 40 introns. The WDR9 cDNA has a size of 13 kb and encodes for a putative protein of 2269 amino acids with a potential location in the nucleus. Expression analysis in different human adult tissues and in cultured cell lines indicates that the gene has several tissue-specific transcripts. The more significant protein signatures in the WDR9 protein sequence are for WD repeats, bromodomain, beta-ketoacyl synthases, and ribonucleoprotein (RNP). The WDR9 protein has a high similarity with the Mus musculus neuronal differentiation protein (NDRP) and a region of similarity with the region of the Yotiao protein that has been proposed to bind the NR1 subunit of the NMDA receptor. The presence of protein-protein interaction domains as such the WD repeats, and the similarity of the WDR9 protein to regulatory proteins suggest a potential involvement in some of the clinical features associated to the DCR-2.

The identification of a novel human homologue of the SH3 binding glutamic acid-rich (SH3BGR) gene establishes a new family of highly conserved small proteins related to Thioredoxin Superfamily.

The SH3 binding glutamic acid-rich (SH3BGR) gene was cloned in an effort to identify genes located to human chromosome 21, within the congenital heart disease region, and expressed in the developing heart. After the identification of SH3BGR, two human homologous genes, SH3BGRL and SH3BGRL3, were identified and mapped to chromosome Xq13.3 and 1p34.3-35, respectively. SH3BGRL and SH3BGRL3 code for small proteins similar to the N-terminal region of the SH3BGR protein. SH3BGRL3 protein shows a significant similarity to Glutaredoxin 1 of Escherichia coli, and all the three proteins are predicted to belong to Thioredoxin-like protein Superfamily. Here we describe the identification and characterization of an additional human homologue of SH3BGR, named SH3BGRL2. The SH3BGRL2 gene maps to chromosome 6q13-15 and its messenger RNA has a large 3' untranslated region containing several AUUUA repeats. SH3BGRL2 codes for a protein of 107 amino acids, which, like SH3BGRL and SH3BGRL3 proteins, is highly homologous to the N-terminal region of the SH3BGR protein and appears to be related to Glutaredoxins and to PKC-interacting cousin of thioredoxin homology domain. We propose that the identification of SH3BGRL2 establishes a novel family of human genes, coding for highly conserved small proteins belonging to Thioredoxin-like protein Superfamily.