Retinoid-independent motor neurogenesis from human embryonic stem cells reveals a medial columnar ground state.

A major challenge in neurobiology is to understand mechanisms underlying human neuronal diversification. Motor neurons (MNs) represent a diverse collection of neuronal subtypes, displaying differential vulnerability in different human neurodegenerative diseases. The ability to manipulate cell subtype diversification is critical to establish accurate, clinically relevant in vitro disease models. Retinoid signalling contributes to caudal precursor specification and subsequent MN subtype diversification. Here we investigate the necessity for retinoic acid in motor neurogenesis from human embryonic stem cells. We show that activin/nodal signalling inhibition, followed by sonic hedgehog agonist treatment, is sufficient for MN precursor specification, which occurs even in the presence of retinoid pathway antagonists. Importantly, precursors mature into HB9/ChAT-expressing functional MNs. Furthermore, retinoid-independent motor neurogenesis results in a ground state biased to caudal, medial motor columnar identities from which a greater retinoid-dependent diversity of MNs, including those of lateral motor columns, can be selectively derived in vitro.

Polypropylenimine dendrimer-induced gene expression changes: the effect of complexation with DNA, dendrimer generation and cell type.

Polypropylenimine (PPI) dendrimers appear attractive non-viral vectors for the delivery of genes, antisense oligonucleotides, and small interfering RNA (siRNA). However, the effects of these synthetic gene delivery vectors on global gene expression are poorly understood. Here we have examined the toxicogenomics of generation 2 (DAB-8) and generation 3 (DAB-16) PPI dendrimers in two human cell lines. At concentrations and treatment protocols routinely used for gene and oligonucleotide transfection, PPI dendrimers alone elicited marked changes in endogenous gene expression in A431 epithelial cells. The extent of PPI-induced gene changes appeared to be dependent on the dendrimer generation as the number of genes affected was greater with G3 compared to G2 PPI dendrimers in A431 cells. The signature of DAB16-induced gene changes in A549 cells was different to those elicited in A431 cells implying a strong dependence on cell type. The DAB-16 polymer complexed with DNA (dendriplexes) also elicited marked gene expression changes in A549 cells but with a signature that was different from the polymer alone implying that dendriplexes are "recognised" by cells as chemical entities that are distinct from the polymer alone. Alterations in expression of a variety of gene ontologies were observed including those involved in defence responses, cell proliferation and apoptosis. Although there was a tendency for increased DNA damage in cells treated with DAB16 alone or its DNA dendriplexes as detected by the COMET assay, these differences were not statistically significant. These data show for the first time that PPI-dendrimers, separate from their capability as transfection reagents, can intrinsically alter the expression of many endogenous genes that could potentially lead to them exerting multiple biological effects in cells. The impact and consequences of polymer-induced gene changes should guide their rational use as delivery systems for gene-based therapeutics.

Caveolin-1 expression and caveolae biogenesis during cell transdifferentiation in lung alveolar epithelial primary cultures.

Caveolae are omega-shaped invaginations of the plasmalemma possessing a cytoplasmic membrane protein coat of caveolin. Caveolae are present in the in vivo alveolar epithelial type I (ATI) lung cell, but absent in its progenitor, the alveolar epithelial type II (ATII) cell. In primary culture ATII cells grown on a plastic substratum acquire with time an ATI-"like" phenotype. We demonstrate that freshly isolated rat ATII cells lack caveolae and expression of caveolin-1 (a critical caveolae structural protein). As the ATII cells acquire an ATI-like phenotype in primary culture caveolin-1 expression increases, with caveolin-1 signal at 192 h postseeding up to 50-fold greater than at 60 h; caveolae were morphologically evident only after 132 h. When maintaining the differentiated ATII phenotype with time, i.e., culture upon collagen with an apical interface of air, a temporal increase in caveolin-1 expression was not observed, with only very faint signals evident even at 192 h postseeding; at no time did these cultures display caveolae. In late primary ATII cultures caveolin-1 expression and caveolae biogenesis occur as a function of in vitro transformation from the ATII to the ATI-like phenotype. The results have broad implications for the in vitro study of the role of caveolae and caveolin in alveolar epithelial cell biology.