Analytical approaches to photobiological hydrogen production in unicellular green algae

Photosynthesis Research - Several species of unicellular green algae, such as the model green microalga Chlamydomonas reinhardtii, can operate under either aerobic photosynthesis or anaerobic...     

Exploring Functional β-Cell Heterogeneity In Vivo Using PSA-NCAM as a Specific Marker

Background

The mass of pancreatic β-cells varies according to increases in insulin demand. It is hypothesized that functionally heterogeneous β-cell subpopulations take part in this process. Here we characterized two functionally distinct groups of β-cells and investigated their physiological relevance in increased insulin demand conditions in rats.

Methods

Two rat β-cell populations were sorted by FACS according to their PSA-NCAM surface expression, i.e. β^high and β^low-cells. Insulin release, Ca²⁺ movements, ATP and cAMP contents in response to various secretagogues were analyzed. Gene expression profiles and exocytosis machinery were also investigated. In a second part, β^high and β^low-cell distribution and functionality were investigated in animal models with decreased or increased β-cell function: the Zucker Diabetic Fatty rat and the 48 h glucose-infused rat.

Results

We show that β-cells are heterogeneous for PSA-NCAM in rat pancreas. Unlike β^low-cells, β^high-cells express functional β-cell markers and are highly responsive to various insulin secretagogues. Whereas β^low-cells represent the main population in diabetic pancreas, an increase in β^high-cells is associated with gain of function that follows sustained glucose overload.

Conclusion

Our data show that a functional heterogeneity of β-cells, assessed by PSA-NCAM surface expression, exists in vivo. These findings pinpoint new target populations involved in endocrine pancreas plasticity and in β-cell defects in type 2 diabetes.     

A mutant of the green alga Dunaliella salina constitutively accumulates zeaxanthin under all growth conditions

A novel mutant (zea1) of the halotolerant unicellular green alga Dunaliella salina is impaired in the zeaxanthin epoxidation reaction, thereby lacking a number of the beta-branch xanthophylls. HPLC analysis revealed that the zea1 mutant lacks neoxanthin (N), violaxanthin (V) and antheraxanthin (A) but constitutively accumulates zeaxanthin (Z). Under low-light physiological growth conditions, the zea1 (6 mg Z per g dry weight or 8 x 10(-16) mol Z/cell) had a substantially higher Z content than the wild type (0.2 mg Z per g dry weight or 0.5 x 10(-16) mol Z/cell). Lack of N, V, and A did not affect photosynthesis or growth of the zea1 strain. Biochemical analyses suggested that Z constitutively and quantitatively substitutes for N, V, and A in the zea1 strain. This mutant is discussed in terms of its commercial value and potential utilization by the algal biotechnology industry for the production of zeaxanthin, a high-value bioproduct.     

Pattern of bone markers during pregnancy and their changes after delivery

OBJECTIVE: To investigate whether bone resorption markers change during pregnancy and lactation, and how they are correlated with human placental lactogen (hPL) and PRL. SUBJECTS: Young women before pregnancy, during pregnancy and during a 12-month post-delivery period (study group; n = 22); and age- and weight-matched normal cycling women (control group; n = 22) for a 20-month-period participated in the study. RESULTS: In the study group, women both during pregnancy (from the 8th up to the 38th week) and during a 6-month period of lactation, pyridinoline and deoxypyridinoline urinary levels were significantly higher than those of pre-pregnancy and control women. They returned to basal values at the 12th post-delivery month. During pregnancy there were early and late peak increases, at the 8th and 32nd week, respectively. At the 32nd, 34th, 36th and 38th week of pregnancy, pyridinoline and deoxypyridinoline urinary values were significantly correlated with hPL serum levels. CONCLUSIONS: During pregnancy the maternal bone resorption seems to vary critically at early and late stages. A complete reversal of these variations seems to occur after lactation. Further studies could evaluate if changes in placental function are capable of differently interfering with maternal bone resorption.     

Oxygenation and microcirculation during skin stretching in undermined and nonundermined skin

The aim of this experimental study was to assess the skin microcirculation of undermined and nonundermined wound edges closed with a skin-stretching device. In eight piglets, 9 x 9-cm wounds were created on both flanks by excision of the skin and the subcutaneous layer down to the muscular fascia, with general anesthesia. On one flank, the surrounding skin was completely undermined. For a period of 30 minutes, wound closure was performed with a stretching device, using the principle of load cycling. The device stretched the skin and moved the opposing wound edges toward each other. During this period, laser Doppler flowmetry and transcutaneous oximetry were simultaneously used to monitor microcirculation and oxygenation in the stretched skin of both flanks. Undermining of the surrounding skin produced a 12 percent decrease in the laser Doppler flowmetry signal and a 21 percent decrease in the transcutaneous oximetry value. Skin stretching resulted in decreases in the laser Doppler flowmetry signals and the transcutaneous oximetry values, whether or not the skin was undermined. Releasing the stretching device resulted in rapid normalization of the laser Doppler flowmetry values in undermined and nonundermined skin and a slow return of the transcutaneous oximetry values to close to baseline levels in nonundermined skin. The transcutaneous oximetry values in undermined skin did not return to baseline levels; each period of skin stretching resulted in an additional decrease in the transcutaneous oximetry values. Stretching of undermined skin for 30 minutes produced a significant (p < 0.0001) decrease in skin oxygenation. As a result, 50 percent of the undermined stretched skin demonstrated skin necrosis at the wound edges, which was still present after 1 week. Wound healing in the nonundermined stretched skin proceeded without problems. It is concluded from these experiments that the viability of undermined skin becomes compromised as a result of significantly decreased oxygen availability in the skin during and after stretching. Consequently, it is recommended that skin stretching be performed on nonundermined skin, rather than undermined skin. In addition, when skin is stretched to close a large defect, it is logical to use cyclic loading, so that recuperation of the skin circulation can occur. Furthermore, laser Doppler flowmetry seemed to produce atypical signals in monitoring of skin viability of wound edges closed with a skin-stretching device.     

Gene expression in human cells with mutant insulin receptors

Insulin initiates its action by interacting with specific receptors on the plasma membrane of target cells. Mutations in these receptors cause the inherited insulin-resistant syndrome leprechaunism. Affected patients have severe intrauterine and post-natal growth restriction coupled with severe metabolic abnormalities. Fibroblasts from patients with leprechaunism have impaired in vitro growth, reflecting the growth restriction seen it in vivo. To determine the reason for the defective growth of cells from patients with mutant insulin receptors, gene expression was compared among fibroblasts from controls and patients with leprechaunism using DNA microarrays. Of the 12,626 human genes tested, cells from patients with leprechaunism had consistently increased mRNA for 151 genes and decreased mRNA for 51 genes. The level of expression of selected genes was independently confirmed by real time RT-PCR. Leprechaun cells had increased expression of several genes involved in metabolic functions, several of which were not previously known to be regulated by the insulin receptor. The absence of insulin receptors modified the expression of genes controlling apoptosis and cellular growth. Functional analysis indicated that cells from patients with leprechaunism had a normal response to apoptotic stimuli when mitochondrial potential and caspase activity were assayed. About 20% of the genes whose RNA was decreased in leprechaun cells coded for proteins involved in cell growth and differentiation. These results suggest that the insulin receptor is a physiologic regulator of several genes involved in intermediate metabolism even in human fibroblasts. Decreased expression of growth-promoting genes may explain the growth restriction of patients with severe insulin resistance.     

Microalgal biotechnology: Carotenoid production by the green algae<Emphasis Type="Italic">Dunaliella salina</Emphasis>

Unicellular green algae of the genusDunaliella thrive in extreme environmental conditions such as high salinity, low pH, high irradiance and subzero temperatures. Species ofDunaliella are well known in the alga biotechnological industry and are employed widely for the production of valuable biochemicals, such as carotenoids. Some strains ofDunaliella are cultivated commercially in large outdoor ponds and are harvested to produce dry algal meals, such as polyunsaturated fatty acids and oils for the health food industry, and coloring agents for the food and cosmetic industries. During the past decade, the advances in molecular biology and biochemistry of microalgae, along with the advances in biotechnology of microalgal mass cultivation, enabled this microalga to become a staple of commercial exploitation. In particular, the advent of molecular biology and mutagenesis inDunaliella has permitted enhancements in the carotenoids content of this green alga, making it more attractive for biotechnological applications. Accordingly, the present review summarizes the recent developments and advances in biotechnology of carotenoid production inDunaliella.