Molecular cloning, expression and regulation of the avian tubby-like protein 1 (tulp1) gene

The tubby-like protein 1 (tulp1) gene is a member of the tubby multigene family which includes tub, tulp1, tulp2 and tulp3. Human and mouse tulp1 genes were cloned and mutations in tulp1 have been implicated in retinitis pigmentosa in man. Here we report on the cDNA cloning of the chicken tulp1 homologue and its protein product deduced from the nucleotide sequence. The chicken Tulp1 protein comprises 358 amino acids with a calculated molecular mass of 40 kDa. The overall structure of Tub and Tulp proteins, exemplified by the highly conserved C-terminal domain of 255 amino acids and the signature motif KLACE, is also preserved in chicken Tulp1. Phylogenetic analysis demonstrates that chicken tulp1 cDNA and protein are closely related to human and mouse tulp1. In addition, chicken tulp1 mRNA is abundantly expressed in retina similar to tulp1 expression in human and mouse. Two tulp1-specific transcripts of 2 and 3 kb in size were identified that showed differential regulation during embryonic and postnatal development. Finally, tulp1 mRNA was found to be expressed in chicken erythroid cells and upregulated by ligand-activated thyroid hormone receptor (TR alpha/c-erbA).

Thyroid hormone regulates the obesity gene tub

Thyroid hormone T3/T4 is a major regulator of energy metabolism in vertebrates, and defects in thyroid status are frequently associated with changes in body weight. It is demonstrated here that thyroid hormone regulates in vivo and in vitro the tub gene, which when mutated in tubby mice causes obesity, insulin resistance and sensory deficits. Hypothyroidism in rats altered tub mRNA and protein in discrete brain areas. These changes could be attributed to thyroid hormone deficiency since T3/T4 treatment restored normal tub expression. T3 also upregulated tub mRNA within 4-6 h in neuronal cells in culture, suggesting that T3 is a positive regulator of tub gene expression. Thus, these results establish a novel pathway of T3 action and provide an important molecular link between thyroid status and the tubby-associated syndrome.

Polarised expression pattern of focal contact proteins in highly motile antigen presenting dendritic cells

Dendritic cells are professional antigen presenting cells that capture antigens and migrate to lymphoid tissues to elicit specific T cell responses. Here we used an in vitro differentiation system for generating highly motile dendritic cells from chicken bone marrow progenitors by employing the conditional v-Rel estrogen receptor (ER) fusion protein v-RelER. Molecular mechanisms of dendritic cell motility were investigated. Differentiation of v-relER progenitors into dendritic cells is associated with a reduction in cell-cell and cell-extracellular matrix interactions as cells acquire motility. We demonstrate that v-relER progenitors and dendritic cells express several adhesion receptors and components of adhesion complexes. Differentiation of v-relER cells was accompanied by downregulation of focal adhesion kinase (FAK), a key molecule of adhesion complexes, but ectopic FAK expression did not affect cell adhesion and motility. Interestingly, v-relER dendritic cells exhibit a polarised expression pattern of actin and vimentin, with actin being highly concentrated at the leading edge of the cells where lamellipodia are formed. FAK, paxillin and tyrosine phosphorylated proteins are found at both poles of the cell and colocalise with actin at the leading edge, while surface beta1 integrin is confined to the uropod at the rear. CD34(+)stem cell-derived human dendritic cells also exhibited an elongated bipolar morphology, mode of migration and a polarised pattern of actin-vimentin expression similar to v-relER dendritic cells.