Aspects of the biology of Galaxias maculatus.

The biology of three landlocked and a riverine population of Galaxias maculatus were examined in western Victoria, Australia. All systems supported reproducing populations of these fish, including Lake Corangamite which had salinities that on occasion reached 82. Spawning sites in Lake Corangamite were located in adjacent tributaries and not in the main lake as was the case for other populations. The smallest fish were found in the fresh water Lake Purrumbete and the largest in the hypersaline Lake Corangamite. The size at which 50% of the population attained sexual maturity varied across sites, with fish maturing at a smaller size in Lake Purrumbete, followed by the Merri River, Lake Bullen Merri and Lake Corangamite. Condition was higher in the freshwater Lake Purrumbete and there was no relationship between condition and temperature, conductivity, turbidity and pH; but there was a positive relationship between condition and dissolved oxygen. Length frequency analysis suggested that the majority of fishes live for a year.

Establishment and characterization of a retinal Müller cell line.

PURPOSE: Primary cultures of Müller cells have proven useful in cell biologic, developmental, and electrophysiological studies of Müller cells. However, the limited lifetime of the primary cultures and contamination from non-neural cells have restricted the utility of these cultures. The aim of this study was to obtain an immortalized cell line that exhibits characteristics of Müller cells. METHODS: Primary Müller cell cultures were prepared from retinas of rats exposed to 2 weeks of constant light. Cells were immortalized by transfection with simian virus 40. Single clones were obtained by repeatedly passaging cells using cloning wells. Immunocytochemical and immunoblotting studies were carried out with glial fibrillary acidic protein (GFAP)-specific and cellular retinaldehyde-binding protein (CRALBP)-specific antibodies. Transient transfections with CRALBP-luciferase constructs were performed by electroporation. RESULTS: Oncogene transformation resulted in the establishment of a permanent cell line that could be readily propagated. Immunocytochemical and immunoblotting studies demonstrated that the Müller cell line, rMC-1, expressed both GFAP, a marker for reactive gliosis in Müller cells, and CRALBP, a marker for Müller cells in the adult retina. Transient transfection assays showed that promoter-proximal sequences of the CRALBP gene were able to stimulate reporter gene expression in rMC-1. CONCLUSIONS: Viral oncogene transformation has been successfully used to isolate a permanent cell line that expresses Müller cell phenotype. The rMC-1 cells continue to express both induced and basal markers found in primary Müller cell cultures as well as in the retina. The availability of rMC-1 should facilitate gene expression studies in Müller cells and improve our understanding of Müller cell-neuron interactions.

Upregulation of AP-2 in the skin of Xenopus laevis during thyroid hormone-induced metamorphosis.

During amphibian metamorphosis dramatic changes occur in the morphogenesis and differentiation of the epidermis. Concurrently with these changes, the 63 kDa keratin gene is upregulated from low basal levels to high levels. What makes these processes unique is that they are controlled by triiodothyronine (T3) and can be duplicated in cultures of purified epidermal cells. Since there is a 2 day lag period between the addition of T3 and the upregulation of keratin gene expression and terminal differentiation, recent studies have focused on identifying the genes activated during the lag period. We assume that the transcription factors required for upregulation of the keratin gene are induced by T3 during the lag period, and therefore we have cloned the keratin gene so that promoter analyses can be conducted. S1 mapping assays have shown that the same transcription start sites are used during premetamorphosis when the keratin gene is basally expressed, during metamorphosis when it is T3-upregulated, and in the adult epidermis where it is expressed independently of T3. During the early part of the lag period TR beta and AP-2 mRNA levels are upregulated in the epidermis by T3. The transcription factor AP-2 is expressed at high levels in the skin of premetamorphic larvae and induced about fivefold by T3 but is not induced in an epithelial cell line (XL-177). Since the keratin mRNA, AP-2 mRNA, and other genes induced during the lag period are expressed in premetamorphic larvae it appears that T3 functions by upregulating the expression of genes previously activated by a T3-independent process. This preprogramming may account for the tissue specificity of T3 action during metamorphosis.

The Caenorhabditis elegans rol-6 gene, which interacts with the sqt-1 collagen gene to determine organismal morphology, encodes a collagen.

The rol-6 gene is one of the more than 40 loci in Caenorhabditis elegans that primarily affect organismal morphology. Certain mutations in the rol-6 gene produce animals that have the right roller phenotype, i.e., they are twisted into a right-handed helix. The rol-6 gene interacts with another gene that affects morphology, sqt-1; a left roller allele of sqt-1 acts as a dominant suppressor of a right roller allele of rol-6. The sqt-1 gene has previously been shown to encode a collagen. We isolated and sequenced the rol-6 gene and found that it also encodes a collagen. The rol-6 gene was identified by physical mapping of overlapping chromosomal deficiencies that cover the gene and by identification of an allele-specific restriction site alteration. The amino acid sequence of the collagen encoded by rol-6 is more similar to that of the sqt-1 collagen than to any of the other ten C. elegans cuticle collagen sequences compared. The locations of cysteine residues flanking the Gly-X-Y repeat regions of rol-6 and sqt-1 are identical, but differ from those in the other collagens. The sequence similarities between rol-6 and sqt-1 indicate that they represent a new collagen subfamily in C. elegans. These findings suggest that these two collagens physically interact, possibly explaining the genetic interaction seen between the rol-6 and sqt-1 genes.