Do permanent night workers show circadian adjustment? A review based on the endogenous melatonin rhythm

"Permanent" or "fixed" night shifts have been argued to offer a potential benefit over rotating shift systems in that they may serve to maximize circadian adjustment and hence minimize the various health and safety problems associated with night work. For this reason, some authors have argued in favor of permanent shift systems, but their arguments assume at least a substantial, if not complete, adjustment of the circadian clock. They have emphasized the finding that the day sleeps taken between successive night shifts by permanent night workers are rather longer than those of either slowly or rapidly rotating shift workers, but this could simply reflect increased pressure for sleep. The present paper reviews the literature on the adjustment to permanent night work of the circadian rhythm in the secretion of melatonin, which is generally considered to be the best known indicator of the state of the endogenous circadian body clock. Studies of workers in "abnormal" environments, such as oil rigs and remote mining operations, were excluded, as the nature of these unique settings might serve to assist adjustment. The results of the six studies included indicate that only a very small minority (<3%) of permanent night workers evidence "complete"adjustment of their endogenous melatonin rhythm to night work, less than one in four permanent night workers evidence sufficiently "substantial" adjustment to derive any benefit from it, there is no difference between studies conducted in normal or dim lighting, and there is no evidence of gender difference in the adjustment to permanent night work. It is concluded that in normal environments, permanent night-shift systems are unlikely to result in sufficient circadian adjustment in most individuals to benefit health and safety.     

Enhanced endocytotic and transcytotic activity in the rat endometrium prior to embryo implantation

Background Understanding the mechanisms by which fluid absorption and secretion occur in the endometrium is clinically important since conditions that deregulate this process reduce fertility. It has been suggested that luminal epithelial cells induce a crucial step in the process of embryo implantation called uterine closure via endocytotic fluid uptake. Uterine lumen closure is a key step in the process of embryo implantation and is absent in some infertile strains of mice. Methods To investigate the process of uterine closure a ferritin-based tracer, used as a marker of endocytosis, was injected into the uterine lumen on day 5 of pregnancy when closure occurs. Results Unexpectedly, luminal epithelial uptake of tracer was minimal on day 5 of pregnancy discrediting endocytosis as the induction method of uterine closure. In contrast, ferritin was found deep in the stromal portion of the endometrium in pre-pregnant animals. Conclusions We have shown for the first time that uterine closure is not induced by luminal epithelial cell driven endocytosis. Another novel finding of this study was the passage of the tracer ferritin up to 15 cells deep into the endometrium suggesting an as yet unstudied mechanism by which information can be transported from the uterine lumen to the underlying stroma.     

The Effect of Activity on the Waking Temperature Rhythm in Humans

Nine healthy female subjects were studied when exposed to the natural light-dark cycle, but living for 17 “days” on a 27h day (9h sleep, 18h wake). Since the circadian endogenous oscillator cannot entrain to this imposed period, forced desynchronization between the sleep/activity cycle and the endogenous circadian temperature rhythm took place. This enabled the effects of activity on core temperature to be assessed at different endogenous circadian phases and at different stages of the sleep/activity cycle. Rectal temperature was measured at 6-minute intervals, and the activity of the nondominant wrist was summed at 1-minute intervals. Each waking span was divided into overlapping 3h sections, and each section was submitted to linear regression analysis between the rectal temperatures and the total activity in the previous 30 minutes. From this analysis were obtained the gradient (of the change in rectal temperature produced by a unit change in activity) and the intercept (the rectal temperature predicted when activity was zero). The gradients were subjected to a two-factor analysis of variance (ANOVA) (circadian phase/ time awake). There was no significant effect of time awake, but circadian phase was highly significant statistically. Post hoc tests (Newman-Keuls) indicated that gradients around the temperature peak were significantly less than those around its trough. The intercepts formed a sinusoid that, for the group, showed a mesor (±SE) of 36.97 (±0.12) and amplitude (95% confidence interval) of 0.22°C (0.12°C, 0.32°C). We conclude that this is a further method for removing masking effects from circadian temperature rhythm data in order to assess its endogenous component, a method that can be used when subjects are able to live normally. We suggest also that the decreased effect of activity on temperature when the endogenous circadian rhythm and activity are at their peak will reduce the possibility of hyperthermia.     

Estimates of the Daily Phase and Amplitude of the Endogenous Component of the Circadian Rhythm of Core Temperature in Sedentary Humans Living Nychthemerally

Fifteen healthy female subjects were studied for eight days while living conventionally. Subjects were free to choose the ways they spent their time within a framework of regular times of retiring and rising; in practice, much of the waking time was spent in sedentary activities. Nine of the subjects were aware of the natural light-dark cycle, this approximating to a 12:12 L:D schedule at the time of year when the study took place. Before the study, subjects were assessed for their degree of "morningness" by questionnaire; throughout the study, they wore a rectal probe, and an activity meter on their non-dominant wrist. The timing (phase) and amplitude of the circadian rectal temperature rhythm were assessed on each day by cosinor analysis as well as by a me thod based on visual inspection of the data. These two parameters were also assessed after the temperature data for each day had been "purified" by a number of methods. From these results it was possible to investigate the effect of purification upon the amplitude of the circadian rhythm of temperature. Also, the day-by-day variability of phase, and the relationship between morningness and phase, were compared using these methods of phase estimation, and using cross-correlation between data sets from adjacent days; in all cases, raw and purified temperature data were used. There was a significantly greater amount of daily variation in phase using purified rather than raw data sets, and this difference was present with all methods of purification as well as with all methods for estimating phase. Purifi cation decreased the amplitude of the circadian temperature rhythm by about 30%. Finally, there was a significant correlation between the morningness score of the subjects and the phase of the circadian temperature rhythm, the phase becoming earlier with increasing morningness; when this relationship was re-examined using purified data, it became more marked. These results reflect the masking effects exerted upon raw temperature data by lifestyle. The extent to which the purification methods enable the endogenous component of a circadian rhythm – and, by implication, the output of the endogenous circadian oscillator – to be estimated in subjects living normally is addressed.     

Genetic diversity of Diaphorina citri (Hemiptera: Liviidae) unravels phylogeographic structure and invasion history of eastern African populations

The Asian citrus psyllid (Diaphorina citri Kuwayama) is a key pest of Citrus sp. worldwide, as it acts as a vector for Candidatus Liberibacter asiaticus, the bacterial pathogen that causes citrus Huanglongbing. Diaphorina citri has been reported in Kenya, Tanzania, and more recently in Ethiopia. This study assessed the genetic diversity and phylogeographic structure of the pest to gain insights into the potential sources of its introduction into Africa. Population structure and differentiation of D. citri populations from China, Ethiopia, Kenya, Tanzania, and the USA were assessed using 10 microsatellite loci. Additionally, five new complete mitogenomes of D. citri collected in China, Ethiopia, Kenya, Tanzania, and the USA were analyzed in the context of publicly available sequences. Genotype data grouped the D. citri populations from Kenya and Tanzania in one cluster, and those from Ethiopia formed a separate cluster. The two genetic clusters inferred from genotype data were congruent with mitochondrial sequence data. The mitogenomes from Kenya/Tanzania/China had 99.0% similarity, and the Ethiopia/USA had 99.9% similarity. In conclusion, D. citri populations in eastern Africa have different sources, as the Kenyan and Tanzanian populations probably originated from southeastern Asia, while the Ethiopian population most probably originated from the Americas.     

Soluble invertase expression is an early target of drought stress during the critical,abortion-sensitive phase of young ovary development in maize

To distinguish their roles in early kernel development and stress, expression of soluble (Ivr2) and insoluble (Incw2) acid invertases was analyzed in young ovaries of maize (Zea mays) from 6 d before (-6 d) to 7 d after pollination (+7 d) and in response to perturbation by drought stress treatments. The Ivr2 soluble invertase mRNA was more abundant than the Incw2 mRNA throughout pre- and early post-pollination development (peaking at +3 d). In contrast, Incw2 mRNAs increased only after pollination. Drought repression of the Ivr2 soluble invertase also preceded changes in Incw2, with soluble activity responding before pollination (-4 d). Distinct profiles of Ivr2 and Incw2 mRNAs correlated with respective enzyme activities and indicated separate roles for these invertases during ovary development and stress. In addition, the drought-induced decrease and developmental changes of ovary hexose to sucrose ratio correlated with activity of soluble but not insoluble invertase. Ovary abscisic acid levels were increased by severe drought only at -6 d and did not appear to directly affect Ivr2 expression. In situ analysis showed localized activity and Ivr2 mRNA for soluble invertase at sites of phloem-unloading and expanding maternal tissues (greatest in terminal vascular zones and nearby cells of pericarp, pedicel, and basal nucellus). This early pattern of maternal invertase localization is clearly distinct from the well-characterized association of insoluble invertase with the basal endosperm later in development. This localization, the shifts in endogenous hexose to sucrose environment, and the distinct timing of soluble and insoluble invertase expression during development and stress collectively indicate a key role and critical sensitivity of the Ivr2 soluble invertase gene during the early, abortion-susceptible phase of development.     

Comparative growth of normal and malignant mouse mammary epithelium cultured serum-free on a biomatrix from preadipocytes

Summary Growth of normal and malignant mouse mammary epithelial cells (MMEC) on a biomatrix of substrate-attached material from 3T3-L1 preadipocytes was evaluated to devise culture conditions that are suitable for transformation studies but do not involve embedding cells in a gel. The biomatrix was prepared as described by Levine and Stockdale (18), and serum-free medium contained bovine serum albumin, insulin, progesterone, prolactin, and linoleic acid. Each cell type produced a distinctive pattern of colony architecture in this culture system. Cells from virgin mice (vMMEC) usually formed elaborate, three-dimensional structures resembling ducts and alveoli; cells from pregnant mice (pMMEC) grew as flat monolayers; and tumor cells grew in multilayered clusters. Cell growth was monitored by an assay for succinate dehydrogenase. Similar growth rates were found through Day 8 in cultures of vMMEC and D2 carcinoma cells. Growth of vMMEC slowed thereafter, whereas tumor cells typically continued growing through Day 14 to 18. Increase in cell number during 18 days in culture was 3-, 7-, 9-, and 11-fold for cells from pregnant and virgin mice, BALB/cfC3H and D2 carcinomas, respectively. The percent cells in S phase on Day 2 of culture was 9% for pMMEC, 4 to 11% for BALB/cfC3H tumor cells, 20% for vMMEC, and 24% for D2 tumor cells. Thus, this culture system promotes extended growth of MMEC and offers several advantages over embedding cells in a collagen gel. It may therefore be applicable to in vitro transformation studies with MMEC. Supported by research grant CA-32937 from the National Institutes of Health, Bethesda, MD, to BBA.     

Thrombospondin sequence motif (CSVTCG) is responsible for CD36 binding.

To clarify the role of CD36 as a TSP receptor and to investigate the mechanisms of the TSP-CD36 interaction, transfection studies were performed using CD36-cDNA in a CDM8 plasmid. Jurkat cells transfected with CD36 cDNA express an 88kD membrane surface protein and acquire the ability to bind thrombospondin. The TSP amino acid sequence, CSVTCG, mediates the interaction of thrombospondin with CD36. CD36 transfectants but not control transfectants bind radiolabeled tyrosinated peptide (YCSVTCG). The hexapeptide inhibits thrombospondin expression on activated human platelets and results in diminished platelet aggregation. CSVTCG-albumin conjugates support CD36-dependent adhesion of tumor cells. We conclude that the CSVTCG repeat sequence is a crucial determinant of CD36 thrombospondin binding.