高等动物细胞核膜和核纤层结构、功能及动态变化调控机制

细胞核是真核细胞中最大的细胞器．高等动物细胞核主要由双层核膜、核孔复合体、核纤层、染色质和核仁等组成．在细胞有丝分裂期,细胞核呈现去装配和再装配等动态变化．在细胞分裂间期,核膜、核孔复合体和核纤层构成细胞核的外周结构,为遗传物质在染色质和核仁中的代谢提供了一个相对稳定的环境,同时调控细胞核内外的物质转运,在细胞增殖、分化、个体发育和细胞衰老等许多方面发挥着重要作用．本文主要对高等动物细胞核膜和核纤层结构、功能及动态变化调控机制等方面的研究进展进行简要综述．     

Greater growth stability of trees in marginal habitats suggests a patchy pattern of population loss and retention in response to increased drought at the rear edge

Species rear range edges are predicted to retract as climate warms, yet evidence of population persistence is accumulating. Accounting for this disparity is essential to enable prediction and planning for species’ range retractions. At the Mediterranean edge of European beech‐dominated temperate forest, we tested the hypothesis that individual performance should decline at the limit of the species’ ecological tolerance in response to increased drought. We sampled 40 populations in a crossed factor design of geographical and ecological marginality and assessed tree growth resilience and decline in response to recent drought. Drought impacts occurred across the rear edge, but tree growth stability was unexpectedly high in geographically isolated marginal habitat and lower than anticipated in the species’ continuous range and better‐quality habitat. Our findings demonstrate that, at the rear edge, range shifts will be highly uneven and characterised by reduction in population density with local population retention rather than abrupt range retractions.     

In vivo dynamics and kinetics of pKi-67: transition from a mobile to an immobile form at the onset of anaphase

A cell proliferation marker protein, pKi-67, distributes to the chromosome periphery during mitosis and nucleolar heterochromatin in the interphase. We report here on the structural domains of pKi-67 that are required for its correct distribution. While both the LR domain and the conserved domain were involved in localization to the nucleolar heterochromatin, both the LR domain and the Ki-67 repeat domain were required for its distribution to the mitotic chromosome periphery. Using in vivo time-lapse microscopy, GFP-pKi-67 was dynamically tracked from the mitotic chromosome periphery to reforming nucleoli via prenucleolar bodies (PNBs). The signals in PNBs then moved towards and fused into the reforming nucleoli with a thin string-like fluorescence during early G1 phase. An analysis of the in vivo kinetics of pKi-67 using photobleaching indicated that the association of pKi-67 with chromatin was progressively altered from "loose" to "tight" after the onset of anaphase. These findings indicate that pKi-67 dynamically alters the nature of the interaction with chromatin structure during the cell cycle, which is closely related to the reformation process of the interphase nucleolar chromatin.     

The intrinsically disorderly story of Ki-67

Ki-67 is one of the most famous marker proteins used by histologists to identify proliferating cells. Indeed, over 30 000 articles referring to Ki-67 are listed on PubMed. Here, we review some of the current literature regarding the protein. Despite its clinical importance, our knowledge of the molecular biology and biochemistry of Ki-67 is far from complete, and its exact molecular function(s) remain enigmatic. Furthermore, reports describing Ki-67 function are often contradictory, and it has only recently become clear that this proliferation marker is itself dispensable for cell proliferation. We discuss the unusual organization of the protein and its mRNA and how they relate to various models for its function. In particular, we focus on ways in which the intrinsically disordered structure of Ki-67 might aid in the assembly of the still-mysterious mitotic chromosome periphery compartment by controlling liquid–liquid phase separation of nucleolar proteins and RNAs.     

Characterization of DIP1, a novel nuclear protein in Drosophila melanogaster

We have recently identified in Drosophila melanogaster a new gene encoding a nuclear protein, DIP1. Here we report the developmental expression and the finding that DIP1 subcellular localization is in the nucleus and at the nuclear periphery during interphase in embryos. Interestingly, in humans, DIP1 antibody identified signals in nuclei from cultured cells and reacted with a rough 30kDa protein in Western blotting experiments, demonstrating evolutionary conservation.     

Decline of the marabou stork (Leptoptilos crumenifer) in West Africa and the need for immediate conservation action

The marabou stork (Leptoptilos crumenifer) is widespread and generally abundant in East and Southern Africa, but recent research has found range loss indicative of a population decline in West Africa in recent decades. In the absence of population data, we conducted an in-depth review of the status of the marabou in the region using a plethora of sources together comprising the largest database on the occurrence of the species. Despite caveats and coarseness of the assessment, we estimate the range loss at 52% in West Africa, including extirpation of approximately 64% of known nesting colonies since 2000. The resulting fragmentation has left a metapopulation of likely no more than 100 breeding pairs in The Gambia and Benin and an unknown number of breeders in Cameroon. Knowledge gaps about marabou population ecology in West Africa are significant and prevent an empirical assessment of regional extinction probability. Therefore, we recommend immediate field surveys, especially for breeding colonies, and research into threats and population dynamics. We also recommend the West African metapopulation be listed as regionally critically endangered and that a working group be formed comprising stakeholders from across the region to aid in assessing threats and implementing research and conservation action.     

A bryophyte flora of Handa Island Sutherland

ABSTRACT

Background: Hybridization is a key driver of plant speciation, and understanding ongoing hybridization provides insights into the underlying process. We studied a hybrid complex in Mediterranean Cyclamen between common C. repandum and rare C. balearicum on Sardinia.

Aims: We analyzed variation in the frequency and morphology of different floral types to assess the degree of hybridization and analyze the ecological niche to better understand factors that influence the maintenance of hybrid populations.

Methods: We recorded the frequency of the different flower color-types in 45 populations and measured floral traits in 10 of them. We characterized the spatial extent and climatic niche of this hybrid complex. We analyzed floral type variation in four traits (flower size, style and anther length, herkogamy).

Results: Hybrid populations occupy a wide area on the NW coast of the island (~1000km2). Sites dominated by hybrid floral types are ecologically marginal for the common parent. The C. repandum-like type is present in all populations and shows a decrease in style and anther length and herkogamy in populations containing a greater proportion of hybrids.

Conclusions: This hybrid complex provides an ideal situation to examine reproductive isolation due to variation in the ecological niche of different floral types.     

Life on the edge: Northern bobwhite ecology at the northern periphery of their range

Over the past 40 years, Northern bobwhite (Colinus virginianus) populations have declined range-wide. The Mid-Atlantic once held the highest densities in the country and now shows some of the worst declines. Although population parameters have been quantified throughout most of the bobwhite range, Mid-Atlantic populations have been largely unstudied. To better quantify the dynamics of this declining system, we sought to not only gather annual data on home range, movement, and habitat selection, but also examine how some of these metrics might impact survival. We captured and radio-tracked 154 bobwhites between May 2006 and April 2008 on a 125 km² area of Cumberland County, New Jersey, USA. Seasonal daily movement ranged from 146 m to 158 m but several extreme movements were notable. Across seasons, grassland habitat was used in greater proportion to its availability, shrub-scrub and agriculture habitats were used equally with their availability and forests and other habitats were used less than their availability. Differences in second-order selection occurred between seasons with lower use of shrub-scrub and forest habitats and higher use of other habitat in breeding seasons. Pooled breeding season survival was 0.343, nonbreeding season survival was 0.183, and annual survival was 0.063. Although mortality was dominated by avian predators, house cat mortalities were noteworthy. Cox proportional hazard analysis revealed that risk of breeding season mortality risk was increased by longer daily movement, lower grassland use, and higher forest and other use. During the nonbreeding season, risk of mortality increased with shorter daily movement and proximity to occupied buildings and barns. This information could inform management decisions in the greater Mid-Atlantic as well as other areas of their range where they exist at very low abundances. © 2010 The Wildlife Society.