Capacitation-like changes occur in mouse spermatozoa cooled to low temperatures

Previously we showed that > 70% of mouse spermatozoa cooled slowly from 37°C to 4°C and warmed have undergone capacitation-like changes as examined by a chlortetracycline staining assay. These membrane changes are reflected in the ability of cooled spermatozoa to achieve fertilization rates in vitro similar to those of uncooled controls when added to oocytes immediately upon warming. The aim of this study was to determine the nature of these membrane changes. We found they were not dependent upon the rate of cooling to 4°C and similar changes were observed when spermatozoa were cooled to higher temperatures (10° and 20°C), but it took longer for 50% of the spermatozoa to undergo such changes (3, 18, and 27 min for spermatozoa held at 4°, 10°, and 20°C, respectively). Mixing cooled spermatozoa with oocytes immediately upon warming produced fertilization rates similar to fresh spermatozoa capacitated in vitro for 90 min before the oocytes were added. The rate of sperm penetration as determined by the fluorescent DNA stain Hoescht 33258 was also similar. However, the penetration time for cooled spermatozoa was significantly shortened when they were preincubated for 90 min before being added to oocytes. We conclude that membrane changes resembling capacitation (1) occur during cooling to temperatures above freezing, (2) are independent of cooling rate, (3) proceed faster at lower temperatures, and (4) obviate the need for prior capacitation in vitro before mixing with oocytes. Mol. Reprod. Dev. 46:318–324, 1997. © 1997 Wiley-Liss, Inc.     

Stat3-dependent induction of interleukin-3 receptor expression in leukemia inhibitory factor-stimulated M1 mouse leukemia cells

M1 mouse leukemia cells differentiate to macrophages/monocytes by the stimulation of interleukin-6 (IL-6)/leukemia inhibitory factor (LIF). To identify new LIF-induced genes, we have performed representational difference analysis using M1 cells and cloned mouse interleukin-3 (IL-3) receptor beta subunit gene. The mRNA expression of both IL-3 receptor (IL-3R) alpha and beta subunits is upregulated after 1 h stimulation of LIF and remains to be elevated along the differentiation of M1 cells. This induction is almost completely suppressed in M1 cells expressing a dominant negative form of Stat3. Furthermore, we show that IL-3-induced Stat5 phosphorylation increases in LIF-stimulated M1 cells. These results suggest that Stat3 may play a role in the differentiation of myeloid cells by regulating IL-3R expression.     

Warmer springs advance the breeding phenology of golden plovers Pluvialis apricaria and their prey (Tipulidae)

Most studies of climate-driven changes in avian breeding phenology have focused on temperate passerines, yet the consequences of such environmental change may be more deleterious for other avian taxa, such as arctic and sub-arctic waders (Charadrii). We therefore examine large-scale climatic correlates of the breeding phenology of one such species (golden plover Pluvialis apricaria), and the timing of emergence of their adult tipulid prey, to assess the potential for climate change to disrupt breeding performance. Golden plover first-laying dates were negatively correlated with both March and April temperature, the mean laying date of first clutches was additionally negatively correlated with March rainfall. The timing of final laying dates were negatively correlated with April temperature only. The timing of tipulid emergence was negatively correlated with May temperature. In combination with historical climatic data, these models suggest a 9-day advancement of golden plover first-laying dates occurred during the 1990s, although this remains within the range of natural variation for the twentieth century. The magnitudes of predicted changes in mean and final laying dates, and the timing of tipulid emergence, were smaller. Climate predictions for 2070-2099 suggest potential advances in first-laying dates by 25 days, whilst the timings of mean and final laying dates are predicted to change by 18 days and 13 days, and tipulid emergence by 12 days. Given the importance of adult tipulids to young golden plover chicks, these changes may result in a mismatch between the timing of first-laying dates and tipulid emergence, so reducing the success of early breeding attempts. Modelling suggests that these changes could reduce breeding success in a South Pennines population by about 11%.     

Insulin at pH 2: structural analysis of the conditions promoting insulin fibre formation

When insulin solutions are subjected to acid, heat and agitation, the normal pattern of insulin assembly (dimers-->tetramers-->hexamers) is disrupted; the molecule undergoes conformational changes allowing it to follow an alternative aggregation pathway (via a monomeric species) leading to the formation of insoluble amyloid fibres. To investigate the effect of acid pH on the conformation and aggregation state of the protein, the crystal structure of human insulin at pH 2.1 has been determined to 1.6 A resolution. The structure reveals that the native fold is maintained at low pH, and that the molecule is still capable of forming dimers similar to those found in hexameric insulin structures at higher pH. Sulphate ions are incorporated into the molecule and the crystal lattice where they neutralise positive charges on the protein, stabilising its structure and facilitating crystallisation. The sulphate interactions are associated with local deformations in the protein, which may indicate that the structure is more plastic at low pH. Transmission electron microscopy analysis of insulin fibres reveals that the appearance of the fibres is greatly influenced by the type of acid employed. Sulphuric acid produces distinctive highly bunched, truncated fibres, suggesting that the sulphate ions have a sophisticated role to play in fibre formation, rather as they do in the crystal structure. Analytical ultracentrifugation studies show that in the absence of heating, insulin is predominantly dimeric in mineral acids, whereas in acetic acid the equilibrium is shifted towards the monomer. Hence, the effect of acid on the aggregation state of insulin is also complex. These results suggest that acid conditions increase the susceptibility of the molecule to conformational change and dissociation, and enhance the rate of fibrillation by providing a charged environment in which the attractive forces between the protein molecules is increased.     

Maternal testosterone in tree swallow eggs varies with female aggression

Variation in the investment of maternal resources in eggs, such as proteins and lipids, can have a profound influence on the growth and development of young. Maternal resources transferred to eggs also include androgens found in the yolk. In several species of birds the concentration of testosterone in the yolk either increases or decreases with laying order. Yolk testosterone has been shown to have various effects on the young including enhanced growth and dominance as well as reduced survival. Previous work suggested that the concentration of testosterone in the yolk may be influenced by the female's social conditions, specifically the frequency of aggressive interactions. In tree swallows, Tachycineta bicolor, we found that yolk testosterone was correlated with the aggressive interactions of the female before and during egg laying. In contrast to other species, yolk testosterone did not vary with laying order in tree swallows. Thus, patterns of yolk testosterone are more variable than thought previously and may be influenced by the social conditions experienced by the female during laying.     

Mating systems, sperm competition, and the evolution of sexual dimorphism in birds

Comparative analyses suggest that a variety of factors influence the evolution of sexual dimorphism in birds. We analyzed the relative importance of social mating system and sperm competition to sexual differences in plumage and body size (mass and tail and wing length) of more than 1,000 species of birds from throughout the world. In these analyses we controlled for phylogeny and a variety of ecological and life-history variables. We used testis size (corrected for total body mass) as an index of sperm competition in each species, because testis size is correlated with levels of extrapair paternity and is available for a large number of species. In contrast to recent studies, we found strong and consistent effects of social mating system on most forms of dimorphism. Social mating system strongly influenced dimorphism in plumage, body mass, and wing length and had some effect on dimorphism in tail length. Sexual dimorphism was relatively greater in species with polygynous or lekking than monogamous mating systems. This was true when we used both species and phylogenetically independent contrasts for analysis. Relative testis size was also related positively to dimorphism in tail and wing length, but in most analyses it was a poorer predictor of plumage dimorphism than social mating system. There was no association between relative testis size and mass dimorphism. Geographic region and life history were also associated with the four types of dimorphism, although their influence varied between the different types of dimorphism. Although there is much interest in the effects of sperm competition on sexual dimorphism, we suggest that traditional explanations based on social mating systems are better predictors of dimorphism in birds.     

Chromosomal rearrangements in Plantago insularis Eastw.

Seeds of Plantago insularis Eastw. which were irradiated with gamma rays yielded 37–67% semi-sterile plants. Twenty-four out of sixty-four of these plants were heterozygous for one or more chromosomal rearrangements. Twothirds of these were translocations, and one-third were inversions. Homozygous lines for four translocations were established. The karyotypes of these provide chromosome markers either at pachynema or in mitotic divisions, or both.Breakage positions were usually located within hetrochromatic segments or at the ends of heterochromatic regions (72.6% of all breaks), and half of all breaks occurred at the juncture of the centromere with the proximal heterochromatin. The consequences of proximal breakage were non-random, in that 93% of such breaks resulted in translocations and only 7% in inversions, whereas more than half of breaks in non-centromeric regions became involved in inversions.The individual chromosomes differed in the types of breakage and of aberrations produced, and these differences appeared correlated with length ratios of heterochromatic segments flanking the centromeres.The research for this paper was supported by National Science Foundation Grant Number GB 5713X.