Homozygous diploid zebra fish have been produced on a large scale by the application of simple physical treatments. Clones of homozygous fish have been produced from individual homozygotes. These clones and associated genetic methods will facilitate genetic analyses of this vertebrate.

Production of clones of homozygous diploid zebra fish ( Brachydanio rerio )

In addition to thick and thin filaments, vertebrate striated muscle contains a third filament system formed by the giant protein titin. Single titin molecules extend from Z discs to M lines and are longer than 1 micrometer. The titin filament contributes to muscle assembly and resting tension, but more details are not known because of the large size of the protein. The complete complementary DNA sequence of human cardiac titin was determined. The 82-kilobase complementary DNA predicts a 3-megadalton protein composed of 244 copies of immunoglobulin and fibronectin type III (FN3) domains. The architecture of sequences in the A band region of titin suggests why thick filament structure is conserved among vertebrates. In the I band region, comparison of titin sequences from muscles of different passive tension identifies two elements that correlate with tissue stiffness. This suggests that titin may act as two springs in series. The differential expression of the springs provides a molecular explanation for the diversity of sarcomere length and resting tension in vertebrate striated muscles.

https://science.sciencemag.org/content/sci/270/5234/293.full.pdf

Titins: Giant Proteins in Charge of Muscle Ultrastructure and Elasticity

A MADS box gene, FLF (for FLOWERING LOCUS F ), isolated from a late-flowering, T-DNA-tagged Arabidopsis mutant, is a semidominant gene encoding a repressor of flowering. The FLF gene appears to integrate the vernalization-dependent and autonomous flowering pathways because its expression is regulated by genes in both pathways. The level of FLF mRNA is downregulated by vernalization and by a decrease in genomic DNA methylation, which is consistent with our previous suggestion that vernalization acts to induce flowering through changes in gene activity that are mediated through a reduction in DNA methylation. The flf-1 mutant requires a greater than normal amount of an exogenous gibberellin (GA3) to decrease flowering time compared with the wild type or with vernalization-responsive late-flowering mutants, suggesting that the FLF gene product may block the promotion of flowering by GAs. FLF maps to a region on chromosome 5 near the FLOWERING LOCUS C gene, which is a semidominant repressor of flowering in late-flowering ecotypes of Arabidopsis.

The FLF MADS Box Gene: A Repressor of Flowering in Arabidopsis Regulated by Vernalization and Methylation

Organization of a mammahan egg at the beginning of development has been the subject of several experimental as well as descriptive cytological and cytochemical investigations. The regulative capacities of blastomeres isolated at the 2-cell stage have been studied in the rat (Nicholas & Hall, 1942), rabbit (Seidel, 1952,1960) and mouse (Tarkowski, 1959 a, b ; Mulnard, 1965 a, b ). Investigations by Seidel and Tarkowski have shown that although the majority of 1/2 blastomeres can regulate and develop into smaller but otherwise normal blastocysts, som e of them give rise to purely trophoblastic vesicles devoid of the inner cell mass. In the mouse, Tarkowski (1959 a, b ) observed in addition in a few cases multicellular morulae which had not undergone cavitation. The findings of Tarkowski have been recently confirmed by Mulnard (1965 a, b ) who studied cytochemically mouse 1/2 blastomeres developing in vitro .

Development of blastomeres of mouse eggs isolated at the 4- and 8-cell stage.

Vertebrate Segmentation: From Cyclic Gene Networks to Scoliosis

The Avian Embryo: Structural and Functional Development

Estimates of the strength of iron binding to model phosphoproteins were obtained from equilibrium dialysis experiments. Iron-free phosvitin (chicken and frog) or alpha sl-casein (cow) was dialyzed against the iron(III) chelates of nitrilotriacetate (NTA), )ethylenedinitrilo)tetraacetate (EDTA), or citrate. Protein-bound metal was measured at equilibrium; competition of chelator and phosphoprotein for iron(III) was determined by reference to comprehensive equilibrium equations presented in the Appendix. Analysis of the iron-binding data for phosvitin suggested that clusters of di-O-phosphorylserine residues (SerP.SerP) were the most probable iron-binding sites. A stoichiometric equilibrium constant of 10(18.0) was calculated for the formation of the Fe3+(SerP.SerP) chelate. When comared on the basis of phosphate content, casein bound iron more weakly than phosvitin. However, if the stoichiometric equilibrium constant for the formation of the casein Fe3+(SerP.SerP) chelate (10(17.5) was adjusted to account for the fact that a smaller percentage of casein phosphoserines occurs in di-O-phosphorylserine clusters, the affinity of casein and phosvitin for iron was very similar. A theoretical comparison showed that the "strengths" of the ferric chelates can be ranked: EDTA greater than phosphoprotein di-O-phosphorylserine greater than citrate greater than NTA.

Iron(III)-phosphoprotein chelates: stoichiometric equilibrium constant for interaction of iron(III) and phosphorylserine residues of phosvitin and casein

Staining acidic phosphoproteins (phosvitin) in electrophoretic gels

https://www.genetics.org/content/genetics/66/2/349.full.pdf

Parthenogenesis and genetic variability. i. linkage and inbreeding estimations in the frog, rana pipiens

An animal enclosure system comprising an enclosure and a modular assembly of enclosures. Each enclosure is adapted so that environmental conditions may be easily and economically changed and conformed to the particular animal in that enclosure. A selection of different levels for the animal and access means for the animal between levels is provided. An adjustable drain and overflow assembly is provided, adapted to permit easy, selective, accurate and reliable adjustment of the water level in the enclosure and to prevent inundation, even if there is a continuous influx of water. Wet-dry environment balance is carefully controllable.

George W. Nace

Papers

The Avian Embryo: Structural and Functional Development

Iron(III)-phosphoprotein chelates: stoichiometric equilibrium constant for interaction of iron(III) and phosphorylserine residues of phosvitin and casein

Staining acidic phosphoproteins (phosvitin) in electrophoretic gels

Parthenogenesis and genetic variability. i. linkage and inbreeding estimations in the frog, rana pipiens

Animal enclosure system