Interplay between low-temperature pathways and light reduction

Low temperature is one of the major factors that adversely affect crop yields by causing restraints on plant growth and productivity. However, most temperate plants have the ability to acclimate to cooler temperatures. Cold acclimation is a process which increases the freezing tolerance of an organism after exposure to low, non-freezing temperatures. The main trigger is a decrease in temperature levels, but light reduction has also been shown to have an important impact on acquired tolerance. Since the lowest temperatures are commonly reached during the night hours in winter time and is an annually recurring event, a favorable trait for plants is the possibility of sensing an imminent cold period. Consequently, extensive crosstalk between light- and temperature signaling pathways has been demonstrated and in this review interesting interaction points that have been previously reported in the literature are highlighted.Key words: cold acclimation, light-reduction, signaling pathways, photoperiodism, circadian clock, light quality     

The ERRalpha orphan nuclear receptor controls morphogenetic movements during zebrafish gastrulation

Gastrulation is a process involving cellular commitment and movements whereby the three fundamental germ layers are established in vertebrates embryos. Estrogen Receptor-Related (ERR) alpha is a nuclear receptor displaying high sequence identity to the Estrogen Receptors (ERs). However, ERRalpha is unable to bind and to be regulated by estrogens or any natural ligand to date. Whereas recent studies have suggested roles for ERRalpha in bone and adipose tissue metabolism in the mouse, little is known about its roles during embryonic development. In zebrafish embryos, ERRalpha is expressed from the beginning of gastrulation at the margin of the blastoderm that represents the presumptive mesendoderm. Using loss of function (morpholinos or a dominant-negative version of the protein) and gain of function (mRNA injection) strategies, we show here that ERRalpha is involved in epiboly and convergent-extension (CE) processes in the zebrafish. Altogether, these results propose ERRalpha as a new regulator of morphogenetic movement during gastrulation, independently of cell fate determination.     

Interplay of DNA repair pathways controls methylation damage toxicity in Saccharomyces cerevisiae

Methylating agents of S(N)1 type are widely used in cancer chemotherapy, but their mode of action is poorly understood. In particular, it is unclear how the primary cytotoxic lesion, O(6)-methylguanine ((Me)G), causes cell death. One hypothesis stipulates that binding of mismatch repair (MMR) proteins to (Me)G/T mispairs arising during DNA replication triggers cell-cycle arrest and cell death. An alternative hypothesis posits that (Me)G cytotoxicity is linked to futile processing of (Me)G-containing base pairs by the MMR system. In this study, we provide compelling genetic evidence in support of the latter hypothesis. Treatment of 4644 deletion mutants of Saccharomyces cerevisiae with the prototypic S(N)1-type methylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) identified MMR as the only pathway that sensitizes cells to MNNG. In contrast, homologous recombination (HR), postreplicative repair, DNA helicases, and chromatin maintenance factors protect yeast cells against the cytotoxicity of this chemical. Notably, DNA damage signaling proteins played a protective rather than sensitizing role in the MNNG response. Taken together, this evidence demonstrates that (Me)G-containing lesions in yeast must be processed to be cytotoxic.     

The mammalian orphan nuclear receptors: orphans as cellular guardians

In classical endocrinology, receptors are molecules that bind a hormone or a ligand to transduce signal within a target cell. Later, however, many intracellular receptors have been discovered in mammals, which have not been shown to bind endogenous ligands and are now are referred as "orphan receptors." The orphan receptors share high degree of structural and functional homology with the classical nuclear receptors (NRs) and are now part of the NR superfamily and therefore referred as orphan nuclear receptors (ONRs). Interestingly, however, ONR members are not evolutionarily or functionally linked and they form a highly diverse group within the NR superfamily. In mammals, ONRs exhibit great functional diversity and majority of them are expressed in a tissue-specific fashion. In the past one decade, functional studies have revealed that they are mediators of multitude of crucial metabolic, developmental, reproductive, and immunological functions in mammals. Emerging studies also indicate the role of ONRs in the onset of several complex human diseases and hence they may be potential candidates for therapeutic drug targeting in the future.     

The mammalian orphan nuclear receptors: orphans as cellular guardians

In classical endocrinology, receptors are molecules that bind a hormone or a ligand to transduce signal within a target cell. Later, however, many intracellular receptors have been discovered in mammals, which have not been shown to bind endogenous ligands and are now are referred as “orphan receptors.” The orphan receptors share high degree of structural and functional homology with the classical nuclear receptors (NRs) and are now part of the NR superfamily and therefore referred as orphan nuclear receptors (ONRs). Interestingly, however, ONR members are not evolutionarily or functionally linked and they form a highly diverse group within the NR superfamily. In mammals, ONRs exhibit great functional diversity and majority of them are expressed in a tissue-specific fashion. In the past one decade, functional studies have revealed that they are mediators of multitude of crucial metabolic, developmental, reproductive, and immunological functions in mammals. Emerging studies also indicate the role of ONRs in the onset of several complex human diseases and hence they may be potential candidates for therapeutic drug targeting in the future.     

Interplay between poxviruses and the cellular ubiquitin/ubiquitin-like pathways

Post-translational polypeptide tagging by conjugation with ubiquitin and ubiquitin-like (Ub/Ubl) molecules is a potent way to alter protein functions and/or sort specific protein targets to the proteasome for degradation. Many poxviruses interfere with the host Ub/Ubl system by encoding viral proteins that can usurp this pathway. Some of these include viral proteins of the membrane-associated RING-CH (MARCH) domain, p28/Really Interesting New Gene (RING) finger, ankyrin-repeat/F-box and Broad-complex, Tramtrack and Bric-a-Brac (BTB)/Kelch subgroups of the E3 Ub ligase superfamily. Here we describe and discuss the various strategies used by poxviruses to target and subvert the host cell Ub/Ubl systems.