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A D Mills

Publications and source records attributed to A D Mills.

At least 37 records · Page 2Linked to original sources
PubMed1993

The role of nucleoplasmin in chromatin assembly and disassembly.

Nucleoplasmin is the most abundant nuclear protein in Xenopus oocytes and eggs. The term 'molecular chaperone' was coined to describe its role in the assembly of the nucleosome subunits of chromatin. Although histones and DNA can self-assemble into nucleosomes, nucleoplasmin can facilitate this process in vitro by competing against non-specific charge interactions. In vivo nucleoplasmin binds histones H2A and H2B and transfers them to DNA. Another acidic nuclear protein, N1, binds and transfers histones H3 and H4. Nucleoplasmin has at least one other role in modulating chromatin structure in Xenopus eggs. It is required for the first stage of sperm chromatin decondensation. It binds and removes sperm basic proteins and replaces them by histones H2A and H2B, again forming nucleosomes, and resulting in decondensation of the compacted sperm chromatin. In addition we propose that the properties of the nuclear localization signal of nucleoplasmin can be explained by a model in which heat shock cognate protein hsc70 has a chaperone role in signal presentation during nuclear transport.

Amino Acid Sequence↗
PubMed1993

Responses to isolation in Japanese quail genetically selected for high or low sociality.

The adrenocortical, behavioral, and leucocytic responses to isolation, for 1, 3, or 72 h, of 7-10-day-old Japanese quail chicks, of lines selected for high (HSR) or low (LSR) levels of social reinstatement (SR) behavior, were studied. Isolation had no effect on plasma corticosterone levels of heterophil/lymphocyte measures in LSR line chicks. Conversely, circulating corticosterone levels were increased after 1 h of isolation in the HSR line, although they fell to control levels thereafter. Heterophil/lymphocyte ratios of HSR line chicks were also increased after 3 h of isolation but decreased to control levels thereafter. Isolated HSR line chicks were consistently more active and showed more peeping and jumping than LSR line chicks in which sitting and lying were more frequent. However, no such behavioral divergence was observed when HSR and LSR line chicks were housed in same-line groups. These results indicate that selection for SR behavior has influenced both underlying social motivation and responses to short-term isolation. Social separation appeared to be more stressful for HSR than LSR line chicks.

Animals↗
PubMed1993

Effects of CRF on isolated Japanese quails selected for fearfulness and for sociality.

The effects of CRF on the behavior and plasma corticosterone levels of isolated Japanese quail chicks were determined. Doses of 15, 30, and 45 micrograms/kg of CRF reduced the number of distress vocalizations emitted during isolation in chicks of a control line. The behavioral responses to a 15 micrograms/kg dose of CRF in lines selected either for high (HSR) or low (LSR) level of sociality or for low (STI) or high (LTI) fearfulness were compared. CRF suppressed vocalizations and increased the number of pecks at food. In LTI and STI chicks, CRF decreased the number of distress calls. In HSR chicks, CRF increased the number of pecks at food and suppressed vocalizations. No effect of CRF was found in LSR chicks. Chicks of the HSR, LSR, LTI, STI, and control lines were injected with 15 micrograms/kg of CRF or saline solution and the level of corticosterone measured following a 15-min isolation period. CRF or isolation alone slightly activated the HPA axis, whereas CRF plus isolation greatly increased corticosterone levels except in the LSR line. These differential responses of LSR chicks and chicks of the other lines, indicate a possible role of CRF in the regulation of social reinstatement behavior.

Animals↗
PubMed1992

Patterns of DNA replication in Drosophila polytene nuclei replicating in Xenopus egg and oocyte extracts.

We have used Xenopus laevis cell-free extracts to study patterns of DNA replication in polytene nuclei isolated from salivary glands of Drosophila melanogaster 3rd instar larvae. Replication was visualized by supplementation with biotin-dUTP so that nascent DNA became labelled, thus allowing detection with fluorescein or Texas-Red-conjugated streptavidin. Biotin incorporation was dependent on incubation in extracts. Transverse bands were labelled in high-speed supernatants of eggs or oocytes in which replication does not initiate de novo. These patterns corresponded to the patterns of endogenous replication forks in polytene nuclei, monitored by bromodeoxyuridine incorporation in intact salivary glands. By contrast, when nuclei were incubated in low-speed supernatants of eggs, they underwent more extensive chromatin decondensation and initiated replication. The spatial patterns of replication are strikingly different from the endogenous patterns. Instead they closely resemble patterns of clustered replication forks seen in Xenopus sperm nuclei replicating in the extract. This indicates that the egg extract can impose its pattern of replication foci even when the template is presented in the highly organized form of a polytene nucleus.

Animals↗
PubMed1991

Genetic and experiential manipulation of fear-related behavior in Japanese quail chicks (Coturnix coturnix japonica).

We examined effects of environmental enrichment and regular handling on fear-related responses in chicks of Japanese quail (Coturnix coturnix japonica) selected over several generations for short or long tonic immobility (STI and LTI, respectively). STI chicks froze less, vocalized and walked sooner and more in an open field, emerged sooner from a hole-in-the-wall box, and showed shorter TI reactions than did chicks of the LTI line. Similarly, environmental enrichment reduced silence and inactivity in the open field, accelerated emergence, and attenuated TI. Regular handling promoted open-field vocalization and reduced the duration of TI but exerted no other significant effects. Principal component analysis showed that the responses in the 3 tests were not independent, which implies that they measured the same underlying factor. The genetic and experiential manipulation of stimulus-specific fears and of general fearfulness is discussed.

Age Factors↗
PubMed1991

Divergent selection for duration of tonic immobility and social reinstatement behavior in Japanese quail (Coturnix coturnix japonica) chicks.

Japanese quail (Coturnix coturnix japonica) were selected over 8 generations for long or short duration of tonic immobility (TI) weighted for independence from social reinstatement (SR) behavior (as measured in a treadmill) and for high or low levels of SR behavior weighted for independence from duration of TI. Divergent selection for long or short duration of TI and for high or low levels of SR behavior resulted in immediate and significant responses that continued throughout the 8 generations. There was no evidence of a plateau in the response to selection in any of the lines. SR responses did not vary in lines selected for duration of TI and vice versa. Selection for short duration of TI led to in an increase in the number of inductions required to induce TI. Selection for low levels of SR behavior led to a decrease in the tendency to move toward conspecifics but not to an increase in the tendency to move away from conspecifics.

Animals↗
PubMed1991

Whitening of brown-shelled eggs: mineral composition of uterine fluid and rate of protoporphyrin deposition.

Changes in the mineral composition of uterine fluid during shell formation and the rates of color appearance and porphyrin deposition on the shell were measured in two subpopulations of brown egg-laying hens with familial histories of low or high incidences of shell whitening. Increases in shell weight and shell breaking strength were correlated with, and proportional to, time spent by the egg in the uterus and were similar in both subpopulations. Shell reflectance decreased and the amount of porphyrin deposited increased linearly 20 to 24 h after oviposition of the preceding egg. Porphyrin deposition was slightly higher at the 23-h stage in the high whitening population but similar amounts of porphyrin were deposited on the shell during the final stage of shell formation in both groups. The coating on the shell responsible for whitening was deposited during the hour prior to oviposition. Uterine fluid pH, pCO2, bicarbonate, and ionized Ca concentrations changed during shell formation but these changes were not related to the incidence of whitening. A milieu supersaturated with calcite solubility product was observed whatever the stage of shell formation. Inorganic phosphorus was not detectable in the uterine fluid whatever the stage of shell formation. The soluble phosphorus fraction of uterine decreased 22 h after oviposition and phosphorus deposition on the shell increased. At the end of egg formation uterine fluid could not be collected. It was concluded that shell whitening was associated with changes in the kinetics of porphyrin deposition rather than with changes in the amount of porphyrin deposited or modifications of uterine fluid composition.

Animals↗
PubMed1990

Association of gold-labelled nucleoplasmin with the centres of ring components of Xenopus oocyte nuclear pore complexes.

We have used heavy-metal shadowing to study the interaction of morphological components of Xenopus oocyte nuclear pore complexes with nucleoplasmin conjugated to colloidal gold. When microinjected into Xenopus oocytes, gold-labelled nucleoplasmin accumulated on the axis of the pores. Envelopes partially disrupted by treatment with low ionic strength buffer produced isolated islands of pores together with substantial quantities of rings deriving from the cytoplasmic and nucleoplasmic faces of the pores. In preparations from oocytes in which nucleoplasmin-gold had been microinjected, most (238/288) of the rings examined had also been labelled and, in the majority of these (60%), the label was located centrally within isolated rings. The central positioning of the nucleoplasmin-gold in isolated rings indicated that these morphological components of the pores were probably involved in the transport of nucleoplasmin into the nucleus, either by way of the initial binding of the molecule or by way of its translocation across the nuclear envelope. Although more work is required to resolve the precise stage at which the rings are involved, a number of lines of evidence suggested that they were more likely to be involved in the translocation step rather than in initial binding of nucleoplasmin.

Animals↗
PubMed1990

Effects of blood sampling on plasma concentrations of corticosterone and glucose in laying hens caged in groups.

1. The effects of taking a blood sample from one bird in a caged group on plasma concentrations of corticosterone and glucose in birds from its own group and birds from other groups were investigated. 2. Two blood sampling protocols were used: successive (all birds within a group were sampled one immediately after another) and alternative (birds from different groups were sampled one after another until all birds in all groups had been sampled). 3. Neither sampling protocol nor between or within group sampling rank was related to plasma concentrations of corticosterone and glucose. 4. The time taken to remove a blood sample (generally more than 45 s but less than 2 min) did not influence circulating corticosterone and glucose. 5. In individual birds plasma concentrations of corticosterone and glucose were poorly correlated with one another. 6. It is concluded that it is possible to take blood samples from a bird, kept in a group, without affecting plasma concentrations of corticosterone and glucose in other birds from that group or in birds from other groups in other cages.

Analysis of Variance↗
PubMed1989

Replication occurs at discrete foci spaced throughout nuclei replicating in vitro.

Demembranated Xenopus sperm nuclei were induced to replicate synchronously in a low-speed supernatant (LSS) of Xenopus eggs by preincubation in a high-speed supernatant (HSS). DNA replication was observed by incorporation of [alpha-32P]dATP, BrdUTP or biotin-dUTP. Biotin-dUTP incorporation, visualised with fluorescent streptavidin, reveals a striking pattern of replication foci throughout replicating nuclei. We show that this represents a precursor to the bright uniform fluorescence seen later. Confocal microscopic analysis of nuclei fixed early in replication reveals that these foci of DNA replication number about 100-300 for each nucleus and probably represent the replicon clusters already described for tissue culture cells. Foci are evenly distributed throughout the nuclei and are not concentrated at or near the nuclear envelope. Complete replication of each nucleus occurs in an average time of only one hour in this system. Hence we calculate that there must be at least 300-1000 replication forks together in each cluster. Furthermore, pulse labelling at later times in the period of replication reveals a similar pattern of foci indicating that replication forks remain tightly clustered in groups of at least 300 throughout the period of DNA replication.

Animals↗
PubMed1988

Nuclear protein migration involves two steps: rapid binding at the nuclear envelope followed by slower translocation through nuclear pores.

When injected into the cytoplasm of Vero cells, nucleoplasmin rapidly concentrates in a narrow layer around the nuclear envelope and then accumulates within the nucleus. Transport into the nucleus can be reversibly arrested at the perinuclear stage by metabolic inhibitors or by chilling. Nucleoplasmin-coated colloidal gold particles concentrate around the nuclear envelope of Vero cells or Xenopus oocytes, and by electron microscopy of oocytes appear to be associated with fibrils attached to nuclear pore complexes. Perinuclear accumulation is not observed for the nonmigrating nucleoplasmin core fragment or nonnuclear proteins. We propose two steps in nuclear migration of proteins: rapid binding around the nuclear envelope, possibly to pore-associated fibrils, followed by slower, energy-dependent translocation through nuclear pores.

Adenosine Triphosphate↗
PubMed1988

Steps in the assembly of replication-competent nuclei in a cell-free system from Xenopus eggs.

We have studied the pathway of nuclear assembly from demembranated sperm chromatin by fractionating a cell-free system from Xenopus eggs (Lohka, M. J., and Y. Masui. 1983. Science (Wash. DC). 220:719-721). Both the soluble fraction and a washed vesicular fraction are required for formation of normal nuclei that initiate replication in vitro. The soluble fraction alone decondenses chromatin and the vesicular fraction alone surrounds chromatin with membranes. Both fractions are required for formation of nuclear pore complexes. Recombining these two fractions recovers approximately 100% of the nuclear assembly and DNA replication activities. Restricting the proportion of the vesicular fraction slows acquisition of the nuclear membrane and allows observation of immature nuclear pores ("prepores"). These form as arrays around and within the chromatin mass before membranes form. Subsequently membrane vesicles bind to these prepores, linking them by a single membrane throughout the chromatin mass. At the periphery this single membrane is surrounded by an outer membrane. In mature nuclei all membranes are at the periphery, the two membranes are linked by pores, and no prepores are seen. Nuclear assembly and replication are inhibited by preincubating the chromatin with the vesicular fraction. However nuclear assembly is accelerated by preincubating the condensed chromatin with the soluble fraction. This also decreases the lag before DNA replication. Initiation of DNA replication is only observed after normal nuclei have fully reassembled, increasing the evidence that replication depends on nuclear structure. The pathway of nuclear assembly and its relationship to DNA replication are discussed.

Animals↗
PubMed1987

Chromosome replication in cell-free systems from Xenopus eggs.

Cell-free systems from eggs of the frog Xenopus laevis are able to perform most of the acts of eukaryotic chromosome replication in vitro. This now includes the crucial regulatory step of initiation, which had only been achieved for viral systems previously. Purified DNA or nuclei are able to initiate and complete semi-conservation replication in egg extracts in vitro (Blow & Laskey, Cell 47, 557-587 (1986). Replication does not require specialized DNA sequences either in vitro or in microinjected eggs, but in both systems large templates replicate more efficiently than small templates. In some cases replication can re-initiate, excluding the possibility that replication is primed by preexisting primers in the template preparations. When nuclei are replicated in vitro, only one round of replication is observed in a single incubation resembling the single round of replication observed for purified DNA after micro-injection. The mechanism that prevents re-initiation of replication within a single cell cycle is discussed and certain models are eliminated. Nucleosome assembly from histones and DNA has also been studied in cell-free systems from Xenopus eggs. Fractionation has led to the identification of two acidic proteins called nucleoplasmin and N1, which bind histones and transfer them to DNA. The sequences of both proteins have been determined by cDNA cloning and sequencing. Both proteins are found as complexes with histones in eggs.

Animals↗
PubMed1987

Extraneous egg shell calcification as a measure of stress in poultry.

The incidence of eggs showing abnormal shell calcification amongst those produced by hens kept in individual battery cages, hens kept in battery cages in groups of 3 and hens kept in battery cages in groups of 4 was studied. There was good agreement between observers in the assessment of abnormal eggs. Hens kept in individual cages laid fewer abnormal eggs than hens kept in groups of 3 or 4. There was no significant difference in the incidence of abnormal eggs between hens kept in groups of 3 or 4. The results of this study support the idea that the incidence of eggs showing abnormal calcification may provide a quick and reliable method of measuring stress in hens which lay brown shelled eggs.

Animals↗
PubMed1985

Heart rate and laying behavior in two strains of domestic chicken.

The heart rates of caged hens, from two strains of domestic chicken (Gallus gallus domesticus), during the 20 min before and after oviposition were studied. Heart rates were measured using subcutaneously implanted radiotelemetry devices. In one strain, heart rate was low and relatively constant before laying, increased sharply at the moment of laying, and then decreased gradually during the post-laying period. Hens from this strain exhibited sitting behavior before laying. In contrast, in the other strain, heart rates increased steadily during the pre-laying period, peaked sharply at the moment of laying, and then declined during the post-laying period. Hens from this strain exhibited restless pacing behavior before laying.

Animals↗
PubMed1985

Genetic analysis of strain differences in pre-laying behaviour in battery cages.

The behaviour of hens of two strains during the 10 min before laying in battery cages was studied. Hens of one strain typically exhibited backward-and-forward pacing before laying. Hens of the other strain did not pace and tended to sit. Individual hens of both strains were consistent in their expression of pacing and sitting before laying. There was genetic variation in the expression of both pacing and sitting before laying, and both traits responded to selection. Crosses between the two lines indicated additive genetic variation in the expression of sitting behaviour and non-additive variation in the expression of pacing behaviour.

Animals↗
PubMed1985

Pre-laying behaviour in battery cages.

The pre-laying behaviour of hens from two strains of domestic fowls housed in battery cages was studied. Hens from one strain exhibited stereotyped pacing before laying, whereas hens from the other tended to sit during the pre-laying period. Hens from both strains performed vacuum nest-building behaviour before laying. Implications of these findings in relation to the improvement of animal welfare are discussed.

Animals↗