Lens regeneration in adult newts is a classic example of faithfully regenerating an entire organ via transdifferentiation1-6. After lentectomy, intriguing regulation allows the pigment epithelial cells (PECs) of the dorsal iris, but not the ventral, to dedifferentiate and then differentiate to form a new lens. This regulation might provide clues to the lack of lens regeneration in higher vertebrates. Six-3 and pax-6 known for their ability to induce ectopic lenses during embryogenesis7,8 and members of the BMP pathway, which are regulators of the dorsal/ventral axis establishment in embryos9 were examined for their role in induction of lens regeneration. Here we show that lens regeneration from the ventral iris is possible by inhibiting the BMP pathway or by transfecting ventral iris cells with six-3 and concomitant treatment with retinoic acid. In intact irises six-3 is expressed higher in the ventral iris. During regeneration, however, only levels in the dorsal iris are significantly increased. Such an increase is seen in ventral irises only when they are induced to transdifferentiate by six-3/RA or BMP inhibitors. Therefore, transcriptional regulation associated with competency for lens regeneration, aims to increase levels over established thresholds and not to merely render a regulatory gene as dorsal-specific. Lack of induction in the axolotl, a salamander incapable of lens regeneration seems to be associated with repression of six-3 expression.

A gram-negative bacterium, Sphingomonas sp. strain A1, isolated as a producer of alginate lyase, has a characteristic cell envelope structure and forms a mouth-like pit on its surface. The pit is produced only when the cells have to incorporate and assimilate alginate. An alginate uptake-deficient mutant was derived from cells of strain A1. One open reading frame, algS (1,089 bp), exhibiting homology to the bacterial ATP-binding domain of an ABC transporter, was cloned as a fragment complementing the mutation. algS was followed by two open reading frames, algM1 (972 bp) and algM2 (879 bp), which exhibit homology with the transmembrane permeases of ABC transporters. Disruption of algS of strain A1 resulted in the failure to incorporate alginate and to form a pit. Hexahistidine-tagged AlgS protein (AlgS His6 ) overexpressed in Escherichia coli and purified by Ni 2؉ affinity column chromatography showed ATPase activity. Based on these results, we propose the occurrence of a novel pit-dependent ABC transporter system that allows the uptake of macromolecules.Alginate is a heteropolysaccharide consisting of ␣-L-mannuronate and its 5Ј-epimer, ␣-L-guluronate, and is produced by brown seaweeds and certain bacteria. Other than its utilization in the medical, chemical, and food areas, this biopolymer has been widely associated with chronic Pseudomonas aeruginosa infection in the lungs of cystic fibrosis patients (5). A bacterium, Sphingomonas sp. strain A1, was isolated from soil as a potent producer of alginate lyase catalyzing the depolymerization of alginate (24). The cells of strain A1 are covered by many large plaits (Fig. 1a), and a mouth-like pit (0.02 to 0.1 m in diameter) is formed on their surface when they are grown in a medium containing alginate as the sole carbon source (10, 11) ( Fig. 1b and c). The pit formed in the presence of alginate disappears when the cells are transferred to a medium without alginate (10, 11). In the presence of alginate, a specific region of the cell surface and its neighborhood is intensely stained with an agent that interacts with mucopolysaccarides (alginate), and thin sections of cells show an irregular site where the cell membrane sinks deeply into the cytosol (10, 11).For the utilization of polysaccharides and other macromolecules, microbes usually degrade them by means of extracellular enzymes and then take the depolymerized low-molecular-weight (LMW) products up through their membranes. However, alginate lyase is exclusively localized in the cytoplasm, and the periplasmic and membrane fractions contain no alginate lyase activity (25). Furthermore, no extracellular alginate-depolymerizing activities have been detected in concentrated culture fluid of strain A1 (24, 25), when assayed by measuring the changes in viscosity and absorbance at 235 nm (for alginate lyase) or analysis of the depolymerization profile by thin-layer chromatography (data not shown). The amino acid sequence of alginate lyase purified from strain A1 was 53 amino acids shorter in the N-terminal region than t...

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