recent studies have uncovered crucial roles for polyploidization in compensatory cell growth during tissue regeneration in the heart, liver, epidermis and intestine. Here, we review current knowledge of the molecular pathways that generate polyploidy and discuss how polyploidization is used in tissue repair and regeneration.

alternative mechanisms may be expressed under different environmental and host conditions or even at different host surfaces. Hence, several adherence mechanisms acting col-laboratively may define where a specific pathogen will colonize and begin to cause an infection. One supposes that microbial attachment mechanisms are usually designed to

Certain diseases can cause the clotting mechanism to malfunction. In these cases, a clot might form for no reason. 8. Finally, apomixis is a particularly favorable mechanism to ensure reproduction after polyploidization.

As a result, the new polyploid is genetically isolated from its diploid progenitor(s) and a new species is formed. cytes, for which the fact but not necessarily the mechanism of their polyploidization is known, these terms are also used in a haphazard fashion. As they were originally defined, these terms may, in fact, no longer apply to the very cells for which they are most often used. Endomitosis, for in-stance, is most often used in reference to the The model proposed suggests that polyploidy should be most common in: (i) populations exposed to environmental fluctuations during their breeding season that may induce higher frequencies of unreduced gametes; (ii) organisms producing sufficient numbers of gametes that random meiotic problems can be filtered; and (iii) in organisms for which mechanisms to promote assortative mating have the capacity to change as a direct consequence of polyploidization. Polyploidization is widespread in plants and animals, and is an important mechanism of speciation.

Ischemia or ischaemia is a restriction in blood supply to tissues, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems with blood vessels, with resultant damage to or dysfunction of tissue.

Common bread wheat (Triticum aestivum) is an example of a common amphiploid. This hexaploid came into being about 7,000 years ago from hybridization between rivet wheat ( T. turgidum ), a tetraploid, and Tausch's goatgrass ( Aegilops tauschii ), a diploid. 5 In fact, Talbert et al. (1998) say it arose repeatedly as the result of multiple hybridization events.

Mechanisms whereby nerve growth factor increases diacylglycerol levels in differentiating PC12 cells Jianxue Li, Richard J. Wurtman) Department of Brain and Cogniti˝e Sciences, E25-604, Massachusetts Institute of Technology, Cambridge, MA 02139, USA Accepted 17 November 1998 Abstract

However, the kinetics of polyploidization differs somewhat between mice and rats. Whereas polyploidization begins at weaning in rats, nearly half of mouse hepatocytes are already polyploid at this time [21]. Polyploidization is common among plants and some animals, and is considered a major speciation and evolution mechanism for diversity. Triploids, however, confront problems of chromosomal pairing and segregation during meiosis, which may cause aneuploid gametes and result in sterility; therefore, triploids are believed to primarily This mechanism produces polyploid offspring that have genetic compositions different from either parent, and often different from the sum of the parents, which allows them to establish successfully and colonize new ecological niches. function of polyploidization Polyploidization, the addition of oneor multiple complete sets of chromosomes, is one of the most dramatic changes known tooccur inthegenome.Surprisingly,thisfascinat-ing phenomenon is well tolerated and common in nature, especially in plants, ﬂies, and fungi [1].

Genome sequencing and related molecular systematics and bioinformatics studies on plants and animals in recent years support the view that species have been shaped by … cellular processes following polyploidization. Moreover, as we highlight here, cellular and organis-mal polyploidy may be manifested as both an effect of environmental stress (i.e., increased rates of polyploidization) and an adaptation to it. This intimate relationship to stress makes the study polyploidy is also far more common than is generally real-ized. mitotic polyploidization, known as acytokinetic mitosis, in- cytes, for which the fact but not necessarily the mechanism of their polyploidization is known, these terms are also used in a haphazard fashion.
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Polyploidization is a common mechanism whereby

(top) Polyploidization may occur developmentally or in response to environmental stress, leading to recurring transcriptional/metabolic changes that confer stress tolerance (purple state). recent studies have uncovered crucial roles for polyploidization in compensatory cell growth during tissue regeneration in the heart, liver, epidermis and intestine. Here, we review current knowledge of the molecular pathways that generate polyploidy and discuss how polyploidization is used in tissue repair and regeneration. Thus the polyploidization event can precede LDD, and one polyploidization event can facilitate a series of LDD events. A more restrictive hypothesis is that LDD events are associated with polyploidization events, thus ploidy changes and LDD co-occur more frequently than expected, and a polyploidization event can be associated with only one LDD event.

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Polyploidization can be a mechanism of sympatric speciation because polyploids are usually unable to interbreed with their diploid ancestors. An example is the plant Erythranthe peregrina . Sequencing confirmed that this species originated from E. × robertsii , a sterile triploid hybrid between E. guttata and E. lutea, both of which have been introduced and naturalised in the United Kingdom .

The stability of and S.bulbocastanum, and present a model whereby autopoly-ploidization triggers, through nucleotide precursor pool imbal-ance, a genomic shock which in turn results in downstream stochastic events responsible for the ‘revolutionary’ phase follow-ing autopolyploidization. Materials and Methods Plant material Irrespective of the mechanism of formation, a key first step in understanding polyploidization is to investigate the geographic distribution of ploidal levels. Examining these distributions are important because many polyploids are cryptic.