Convergent evolution of cysteine residues in sperm protamines of one genus of marsupials, the Planigales

A characteristic feature of the sperm P1 protamines of eutherian mammals is the constant presence of six to nine cysteine residues per molecule. During spermiogenesis these residues become oxidized to form a three-dimensional network of disulfide bridges between, and within, protamine molecules in the sperm chromatin. This covalent cross linking strongly stabilizes eutherian sperm nuclei. In contrast, protamines sequenced from teleost fish, birds, monotremes, and marsupials all lack cysteine residues and their sperm nuclei, without the stabilizing cross links, are easily decondensed in vitro. We have now found that one genus of tiny, shrewlike dasyurid marsupials, the Planigales, possess P1 protamines containing five to six cysteine residues. These residues appear to have evolved since the divergence of Planigales from other members of the family Dasyuridae, such as the marsupial mouse, Sminthopsis crassicaudata. We believe this constitutes a case of convergent evolution in a subfamily of dasyurid marsupials toward the cysteine-rich eutherian form of sperm protamine P1.      

Evidence for independent recruitment of zeta-crystallin/quinone reductase (CRYZ) as a crystallin in camelids and hystricomorph rodents

Zeta-crystallin/quinone reductase (CRYZ) is an NADPH oxidoreductase expressed at very high levels in the lenses of two groups of mammals: camelids and some hystricomorph rodents. It is also expressed at very low levels in all other species tested. Comparative analysis of the mechanisms mediating the high expression of this enzyme/crystallin in the lens of the Ilama (Lama guanacoe) and the guinea pig (Cavia porcellus) provided evidence for independent recruitment of this enzyme as a lens crystallin in both species and allowed us to elucidate for the first time the mechanism of lens recruitment of an enzyme- crystallin. The data presented here show that in both species such recruitment most likely occurred through the generation of new lens promoters from nonfunctional intron sequences by the accumulation of point mutations and/or small deletions and insertions. These results further support the idea that recruitment of CRYZ resulted from an adaptive process in which the high expression of CRYZ in the lens provides some selective advantage rather than from a purely neutral evolutionary process.      

rRNA gene activity and control of expression mediated by methylation and imprinting during embryo development in wheat x rye hybrids

Ribosomal RNA genes originating from one parent are often suppressed in interspecific hybrids. We show that treatments during germination with the cytosine analogue 5-azacytidine stably reactivate the expression of the suppressed rRNA genes of rye origin in the wheat x rye amphiploid, triticale, by preventing methylation of sites in the rye rDNA. When 5-azacytidine is applied to embryos of triticale and wheat x rye F₁ hybrids nine, or more, days after fertilization, rye rRNA gene expression is stably reactivated in the resulting seedling. Earlier treatments have no effect on rye rRNA gene expression, indicating that undermethylation of DNA early in embryo development is reversible. After 9 days, the methylation status of rRNA genes in maintained throughout development. Since the change in expression follows a methylation change at particular restriction-enzyme sites, the data establish a clear correlation between gene activity and methylation in plants.     

Chromosome identification and nuclear architecture in triticale tritordeum F1 hybrids

In situ hybridization with cloned, repetitive DNA probes andtotal genomic DNA enables the parental origin of all chromosomesto be established in metaphases of triticale tritordeum F¹hybrids (2n=6x=42). Nuclei contain seven chromosomes of Hordeumchilense origin, seven from Secale cereale and 28 of wheat origin.When used as a probe, total genomic rye DNA labelled the ryechromosomes strongly and uniformly along their lengths, withbrighter regions coincident with the terminal heterochromatin.The probe labelled the wheat-origin chromosomes weakly and wasalmost undetectable on the H. chilense-origin chromosomes. Incontrast, under the same conditions, H. chilense DNA hybridizedstrongly to the H. chilense- and, with intermediate strength,to the S. cereale-origin chromosomes, excluding the subtelomericheterochromatin: it hybridized only weakly to the wheat chromosomes,in some experiments revealing characteristic bands on wheatchromosomes. Cloned repetitive DNA probes from rye and H. chilensewere used as probes to identify the linkage groups of all oftheir own-species chromosomes. Analysis of hybridization patternsof various probes to prophase and interphase nuclei indicatedthat there are many non-random features in the localizationof both repetitive DNA and whole chromosomes, although generalpatterns of nuclear organization have yet to emerge. Both theparticular lines used and the techniques developed here arelikely to be valuable for production and characterization ofplant breeding material. Key words: In situ hybridization, triticale, cytogenetics, plant breeding, Hordeum chilense     

Ribosomes, membranes and organelles during meiosis in angiosperms.

Evidence is presented from both observational and analytical techniques indicating profound changes to take place in the ribosome population during male and female meiosis in some flowering plants. During microsporogenesis these appear to involve the elimination of the major part of the ribosome complement early in the meiotic prophase, and its subsequent restoration by the disintegration in the tetrad cytoplasm of 'nucleoloids', themselves synthesized in the nucleus during late prophase. In female tissue the process is essentially similar except for differences in the restoration of the ribosome population. Immediately before the eradication of the ribosomes in both sexes, a sizeable proportion of the meiocyte cytoplasm is encapsulated by double, or multiple unit membrane profiles. Significantly this cytoplasm remains unaffected by the agents responsible for the degredation of the ribosome population. These events are also reflected in the organelle populations where cycles of dedifferentiation and redifferentiation take place. In view of evidence from other organisms, it is considered unlikely that these cycles are in any way a prerequisite of meiosis, but more a characteristic of cells undergoing major changes of phase, where a cytoplasmic 'clean-up' is required before the next stage of growth may begin.     

A cytochemical study of the leaf-gland enzymes of insectivorous plants of the genus Pinguicula

Summary Cytochemical methods have been used to study the distribution of acid phosphatase, esterase, ribonuclease, amylase and protease activity in the stimulated and unstimulated leaf glands of Pinguicula grandiflora, P. vulgaris, P. lusitanica, and P. caudata. Two gland types are present, stalked and sessile. The stalked glands bear a muco-polysaccharide secretion droplet, and are concerned with capture of the prey; the sessile glands are specialised for digestion. In unstimulated glands of both classes, acid phosphatase, esterase and ribonuclease activity is associated with the anticlinal walls of the head cells, which have a characteristic spongy inner surface, comparable with that of transfer cells. Acid phosphatase and esterase activity was also detected in the vacuoles of the head cells of the sessile glands. Substrate film tests showed that amylase is readily released from the stalked glands but not from the sessile ones, while in contrast proteolytic activity is mainly associated with the sessile glands.On stimulation by suitable nitrogenous materials, the glands begin to sectete fluid onto the leaf surface within 1 hr. During the process the enzymes held in the spongy walls are discharged, and activity is also lost from the intracellular sites in the sessile glands.Digestion on the leaf surface and resorption of the products has been followed autoradiographically after feeding of ¹⁴C-labelled protein. Within 2 hr, digestion products enter the leaf, and move towards the margin in the vascular system. Movement out of the leaf begins within 12 hr. Microautoradiographs showed a concentration of products around the bases of the sessile glands and in the cells of the gland head, showing that these glands are involved in resorption as well as secretion.A possible mechanism of gland function is discussed.     

Functional changes in human leukemic cell line HL-60. A model for myeloid differentiation

Polar solvents induce terminal differentiation in the human promyelocytic leukemia cell line HL-60. The present studies describe the functional changes that accompany the morphologic progression from promyelocytes to bands and poly-morphonuclear leukocytes (PMN) over 9 d of culture in 1.3 percent dimethylsulfoxide (DMSO). As the HL-60 cells mature, the rate of O(2-) production increase 18-fold, with a progressive shortening of the lag time required for activation. Hexosemonophosphate shunt activity rises concomitantly. Ingestin of paraffin oil droplets opsonized with complement or Ig increases 10-fold over 9 d in DMSO. Latex ingestion per cell by each morphologic type does not change significantly, but total latex ingestion by groups of cells increases with the rise in the proportion of mature cells with greater ingestion capacities. Degranulation, as measured by release of β-glucuronidase, lysozyme, and peroxidase, reaches maximum after 3-6 d in DMSO, then declines. HL-60 cells contain no detectable lactoferrin, suggesting that their secondary granules are absent or defective. However, they kill staphylococci by day 6 in DMSO. Morphologically immature cells (days 1-3 in DMSO) are capable of O(2-) generation, hexosemonophosphate shunt activity, ingestion, degranulation, and bacterial killing. Maximal performance of each function by cells incubated in DMSO for longer periods of time is 50-100 percent that of normal PMN. DMSO- induced differentiation of HL-60 cells is a promising model for myeloid development.