C-type cytochromes from two protozoa, Crithidia oncopelti and Kuglena gracilis. were purified and partly characterised. Crithidia cytochrome C557 and Euglena cytochrome C558 had certain atypical spectral characteristics. The sequence of amino acids in both proteins was determined and compared with the large number of eukaryotic cytochrome c sequences already known. One of the two amino acids which are involved in the covalent attachment of the prosthetic group to the protein in c-type cytochromes is replaced by a non-binding amino acid in both protozoan cytochromes. It is proposed that this change results in the observed spectral peculiarities of these two cytochromes. A second c—type cytochrome, which is implicated in photosynthesis, was isolated from Euglena and the sequence of amino acids was determined. This protein is not closely related in structure to the mitochondrial cytochromes c although certain features are similar. Homology with a prokaryotic c—type cytochrome is proposed, with possible implications for the evolution of photosynthesis.

No description available.

No description available.

Mouse aggregation chimaeras were used in this study to attempt to evaluate the developmental potential of tetraploid cells in the fetus and extraembryonic membranes of mid-gestation chimaeric conceptuses. Diploid͍diploid chimaeras were generated and analysed to provide a control and general baseline for the analysis of tetraploid͍diploid chimaeras. Relationships between compositions of tissues in the diploid͍diploid chimaeras were in agreement with those already established. Tetraploid embryos were produced by electrofusion, which facilitates the fusion of adjacent blastomeres following the exposure to electric field pulses. Three genetic cell markers were chosen to allow identification of the two cell populations in chimaeric conceptuses. These were; (i) pigment in the retinal epithelial cells of the eye; (ii) electrophoretic variants of the enzyme glucose phosphate isomerase (GPI); (iii) the β-globin transgenic marker, which can be detected by <i>in situ</i> hybridization. The bulk of the analysis was performed at 12<SUP>1</SUP>/<SUB>2</SUB> days of gestation by assaying homogenized tissue for GPI. By constructing chimaeras from two embryos which were homozygous for different alleles of <i>Gpi-1</i>, it was possible to estimate the proportions of each cell type in each tissue of the chimaera. <i>In situ</i> hybridization was used to provide spatial information on the yolk sacs of the tetraploid͍diploid chimaeras. The efficiency of the electrofusion technique was tested by <i>in situ</i> hybridization, to ensure that embryos produced by the technique were uniformly tetraploid and not 4m/2n mosaics. In the tetraploid͍diploid chimaeras, the tetraploid cells contributed mainly to the primitive endoderm derivatives (yolk sac endoderm, parietal; endoderm), with very little contribution to the primitive ectoderm derivatives (fetus, amnion, yolk sac mesoderm). There was also good colonisation of the trophectoderm derivatives (trophoblast, placenta).

Triploid human embryos are believed to account for up to 20% of all first trimester spontaneous abortions with a numerical chromosomal abnormality. This group of polyploid embryos therefore gives rise to a significant proportion of human pregnancy wastage. It would appear from cytogenetic studies of human triploid conceptuses that 85% of human triploids are of diandric origin and only 15&37 of digynic origin. Some of these genetic conditions are of considerable clinical significance, since the placentas of human diandric diploids and diandric triploids show 'complete' and 'partial' hydatidiform molar degeneration, respectively. Since the number of human triploid conceptuses obtained in any one centre is generally very limited, and their pre- and early post-implantation stages are simply unavailable for analysis, suitable animal models have been developed to study these genetically abnormal conditions. A study of these triploid conditions has been investigated through the analysis of the appropriate mouse models produced by the expermental techniques indicated below. The relationship between the genetic constitution, morphological appearance and developmental fate of these various types of triploid embryos has been investigated in this study. One of the most informative models we have used is the LT/Sv strin of mice, which regularly ovulate primary oocytes, which are capable to being fertilised and produce digynic triploid embryos. We have also shown that by the administration of exogenous hormones to this strain of mouse the incidence of ovulation of primary oocytes can be increased. It has also been observed that maternal age of the mouse was important in relation to the incidence of primary oocytes ovulated; at 6 weeks old up to 50% of the oocytes ovulated were primary oocytes, significantly lower levels were observed when females were examined at 12, 18, 24 and 30 weeks of age. We have also been able to produce digynic triploid embryos in F1 hybrid female mice by the administration of an intraperitoneal injection of cytochalasin D, which if given at an appropriate time after Human Chorionic Gonadotrophin (HCG) administration, will inhibit the extrusion of the second polar body following fertilisation, and result in the production of up to 18% of digynic triploids.

56 invertebrate species were identified from the sediment at Culbin. There was little evidence of consistent and easily interpretable seasonal cycles for the main invertebrates, but several species tended to have higher abundance during the autumn or early winter. Annual production by invertebrates was 15-23 gAFDW.m-2.yr-1. Arenicola marina was the most important in terms of standing stock in the sediment, followed by the bivalve Cerastoderma edule. Production values of cockles were 1.4-3.4 gAFDW.m-2.yr-1. The most abundant epibenthic species were the brown shrimp Crangon crangon, the common goby Pomatoschistus microps and plaice Pleuronectes platessa, but other fish (e.g. sandeel Ammodytes tobianus, three-spined stickleback Gasterosteus aculeatus, fifteen-spined stickleback Spinachia spinachia, sea scorpion Myoxocephalus scorpio, pipefish Nerophis lumbriciformes, sand goby Pomatoschistus minutus, and flounder Plactichthys flesus), crab (e.g. shore crab Carcinus maenas and hermit crab Pagurus bernhardus ) and starfish (Asterias rubens) were also present. The most important prey were amphipods (mainly Bathyporeia) for the brown shrimp and common goby, and bivalves (siphons of adult individuals) for plaice. Despite the relatively high consumption rates manipulative field experiments showed that none of the predators had significant impact on invertebrate prey densities, although shorebirds had significant size effects on the prey, especially on the larger size classes of the bivalves C. edule and Macoma balthica. These results are in line with others found all around the world such as in the Ythan estuary, Scotland (e.g. Raffaelli & Hall, 1992, Anim. Ecol. 61: 551-560), USA (Wilson, 1994, J. Exp. Mar. Biol. Ecol., 196(1) : 15-25), and in New Zealand (Trush et al., 1994, Mar. Ecol. Prog. Ser., 107(3) : 211-222).

<I>Pax6</I> is a developmentally important, highly conserved transcription factor. <I>Pax6</I> mutations in mouse, man and <I>Drosophila </I>cause eye abnormalities. <I>Pax6</I> mutations in the mouse cause the small eye phenotype. Several small eye alleles have been identified, including <I>Sey </I>and <I>Sey<SUP>Neu</SUP>. </I>The heterozygous small eye mouse (<I>Sey/</I>+) exhibits micropthalmia and anterior segment abnormalities similar to the human conditions of aniridia and Peter's anomaly. The homozygous small eye mouse (<I>Sey/Sey</I>) exhibits anopthalmia, absence of nasal tissues, severe brain defects and cranio-facial abnormalities and is an early post-natal lethal. It is difficult to determine from the small eye homozygous phenotype alone the developmental potential of cells deficient in <I>Pax6</I> during eye and nasal development as the eyes and nasal tissues are completely absent. Therefore, to investigate roles for <I>Pax6 </I>in eye and nasal development, cells deficient for <I>Pax6</I> were incorporated with wild-type cells within aggregation chimaeras. This strategy attempts to rescue <I>Pax6</I> deficient cells into lens and nasal tissue formation. Production of E12.5 <I>Sey<SUP>Neu</SUP>/Sey </I>↔+/+ aggregation chimaeras showed that <I>Sey<SUP>Neu</SUP>/Sey</I> cells were unable to contribute to the lens and nasal epithelium, thus defining a cell autonomous role for <I>Pax6</I> in these tissues. Severe abnormalities of optic cup development were also observed in <I>Sey<SUP>Neu</SUP>/Sey</I> ↔ +/+ chimaeras. Optic cup phenotypes indicated requirements for <I>Pax6</I> in cell-to-cell interaction in the optic cup due to marked segregation between <I>Sey<SUP>Neu</SUP>/Sey </I>cells and wild-type cells. Also, <I>Sey<SUP>Neu</SUP>/Sey</I> cells were found to be excluded from the retinal pigment epithelium (RPE), which indicated a possible cell autonomous role for <I>Pax6</I> in RPE differentiation. Inability of <I>Sey<SUP>Neu</SUP>/Sey</I> cells to contribute to RPE could be due to a failure of mutant cells to be recruited to this differentiation pathway or incomplete or retarded differentiation of <I>Sey<SUP>Neu</SUP>/Sey </I>cells relative to wild-type cells within the chimaeric eye. These possibilities were explored by analysis of expression of <I>Pax6</I> and an early RPE marker, <I>Trp2, </I>in E12.5 and E14.5 <I>Sey<SUP>Neu</SUP>/Sey</I> ↔+/+ chimaeras. These experiments confirmed a role for <I>Pax6</I> in the development of the RPE and indicated that although <I>Sey<SUP>Neu</SUP>/Sey</I> cells were able to be specified as RPE, they were unable to differentiate at the stages examined.

No description available.

No description available.

No description available.