Geographic variation of life‐history traits in the sand lizard,Lacerta agilis: testing Darwin's fecundity‐advantage hypothesis

The fecundity‐advantage hypothesis (FAH) explains larger female size relative to male size as a correlated response to fecundity selection. We explored FAH by investigating geographic variation in female reproductive output and its relation to sexual size dimorphism (SSD) in Lacerta agilis, an oviparous lizard occupying a major part of temperate Eurasia. We analysed how sex‐specific body size and SSD are associated with two putative indicators of fecundity selection intensity (clutch size and the slope of the clutch size–female size relationship) and with two climatic variables throughout the species range and across two widespread evolutionary lineages. Variation within the lineages provides no support for FAH. In contrast, the divergence between the lineages is in line with FAH: the lineage with consistently female‐biased SSD (L. a. agilis) exhibits higher clutch size and steeper fecundity slope than the lineage with an inconsistent and variable SSD (L. a. exigua). L. a. agilis shows lower offspring size (egg mass, hatchling mass) and higher clutch mass relative to female mass than L. a. exigua, that is both possible ways to enhance offspring number are exerted. As the SSD difference is due to male size (smaller males in L. a. agilis), fecundity selection favouring larger females, together with viability selection for smaller size in both sexes, would explain the female‐biased SSD and reproductive characteristics of L. a. agilis. The pattern of intraspecific life‐history divergence in L. agilis is strikingly similar to that between oviparous and viviparous populations of a related species Zootoca vivipara. Evolutionary implications of this parallelism are discussed.     

Genetic analysis of developmental mechanisms in hydra: XIV. Identification of the cell lineages responsible for the altered developmental gradients in a mutant strain,reg-16

The developmental gradients of six chimeric strains of hydra produced from a normal strain (105) and a regeneration-deficient strain (reg-16) were analyzed. The reg-16 mutant has been shown to have a lower gradient of head-activation potential and a higher gradient of head-inhibition potential than the normal 105 strain. The chimeric animals consisted of different combinations of the three self-renewing cell lineages found in hydra (the ectodermal and endodermal epithelial cell lineages and the interstitial cell lineage) from each of the parental origins. To identify the cell lineages responsible for the abnormal gradients in reg-16, the head-activation and head-inhibition potentials of these cell lineage chimeras were assayed by lateral transplantation of tissue. The results obtained have provided evidence which indicates that the defect responsible for the low head-activation potential in reg-16 resides in its ectodermal and endodermal epithelial cell lineages, whereas the defect responsible for its high head-inhibition potential resides in its endodermal epithelial and interstitial cell lineages. The cellular localization of these defects is not identical but very similar to the cellular localization of the regenerative defects in reg-16. This finding is consistent with and supports the view that the abnormalities of the developmental gradients are correlated to the reduced head regenerative capacity in reg-16.     

Altered establishment of cell lineages in theCaenorhabditis elegans embryo after suppression of the first cleavage supports a concentration-dependent decision mechanism

Summary In the early embryo ofCaenorhabditis elegans five somatic cell lineages and a germ cell lineage are established by a series of unequal cleavages in the germline. We suppressed first cleavage by means of cold, mechanical pressure or centrifugation. Thereafter, with the second attempt of the zygote to divide, four blastomeres were generated simultaneously in a tetrapolar cleavage. Cell division pattern, segretation of germline-specific granules, and terminal differentiation of such manipulated embryos were analysed. Instead of six, only from one to five visible cell lineages were established before the germline prematurely aborted from its typical pattern of unequal cleavage. The absence of germline-specific cleavage appears to accompany the abnormal segregation of germline-specific granules. While muscle differentiation was detected even in embryos expressing only one cell lineage, in general, gut differentiation became visible only if a separate gut lineage had been generated. We hypothesize that the potential for differential cleavage is lost in manipulated embryos because a cytoplasmic control factor is diminished as a result of the retarded soma/germline separation. According to this hypothesis, after manipulation, a concentration-dependent decision mechanism leads to: a reduced number of unequal germline cleavages or even none at all, the establishment of fewer distinct cell lineages, and limited cellular differentiation.     

Polymorphism and evolution of vulval precursor cell lineages within two nematode genera, Caenorhabditis and Oscheius

BACKGROUND: The cell lineage of nematodes is mostly invariant for a given species, but varies between species. One can thus wonder how a cell lineage varies during evolution. We have started a microevolutionary approach within two genera by observing lineage variations of vulval precursor cells in different natural nematode populations of the same and closely related species. RESULTS: In Caenorhabditis elegans, the P3.p cell lineage is variable within a genetically homogeneous population and polymorphic between wild strains. Irrespective of its division pattern, P3.p is competent to form vulval tissue in different C. elegans strains, whereas it is not competent in C. briggsae. In Oscheius sp. 1, P4.p and P8.p lineages are strongly polymorphic. Within each genus, these intraspecies polymorphisms in cell lineages are amplified between closely related species. In Oscheius sp. 1, the large polymorphisms in P4.p and P8.p lineages allowed us to undertake a genetic analysis of the variation between two pairs of strains. Multiple loci are involved in cell lineage differences, and variation at one locus appears to have a relatively strong effect. In addition to these large lineage variations in cells that do not normally contribute to the vulva, we find minor variations (errors) in vulval lineages, which represent the precision level of the vulval-patterning process and point to a selection pressure for maintenance of a large vulval equivalence group. CONCLUSIONS: Polymorphisms in vulval cell lineage are found within a given nematode species, and could be instrumental in explaining evolutionary variations between closely related species.     

Intraspecific phylogeny and lineage group identification based on the prfA virulence gene cluster of Listeria monocytogenes

Listeria monocytogenes is a serious food-borne pathogen that can cause invasive disease in humans and other animals and has been the leading cause of food recalls due to microbiological concerns in recent years. In order to test hypotheses regarding L. monocytogenes lineage composition, evolution, ecology, and taxonomy, a robust intraspecific phylogeny was developed based on prfA virulence gene cluster sequences from 113 L. monocytogenes isolates. The results of the multigene phylogenetic analyses confirm that L. monocytogenes comprises at least three evolutionary lineages, demonstrate that lineages most frequently (lineage 1) and least frequently (lineage 3) associated with human listeriosis are sister-groups, and reveal for the first time that the human epidemic associated serotype 4b is prevalent among strains from lineage 1 and lineage 3. In addition, a PCR-based test for lineage identification was developed and used in a survey of food products demonstrating that the low frequency of association between lineage 3 isolates and human listeriosis cases likely reflects rarity of exposure and not reduced virulence for humans as has been previously suggested. However, prevalence data do suggest lineage 3 isolates may be better adapted to the animal production environment than the food-processing environment. Finally, analyses of haplotype diversity indicate that lineage 1 has experienced a purge of genetic variation that was not observed in the other lineages, suggesting that the three L. monocytogenes lineages may represent distinct species within the framework of the cohesion species concept.     

Estimating cell lineage from distributions of randomly introduced markers

Cell lineage of a multicellular organism has been analysed by introducing a genetic or chemical marker that is inherited from a cell to its daughter cells and is detectable even after several cell divisions. To construct a complete cell lineage, all the cells at different developmental stages need to be identified, and then the intracellular marker must be introduced to each cell. In this paper, I study a new method of estimating cell lineage based on distributions of intercellular markers observed at a single stage, which are introduced randomly at earlier stages. Assumptions are: (1) cell lineage is invariant between embryos; (2) a small number of cells are marked in each experiment; and (3) the total number of replicate experiments is sufficiently large. Then we identify the most likely cell lineage pattern (or tree topology) as the one that requires the least marker insertions to be compatible with the observed distributions of cell markers. This method is essentially the same as the principle of persimony widely used for ancestral phylogeny reconstruction in evolutionary biology. When the total number of cells is small, we can generate all the possible cell lineages and calculate the minimum number of marker insertions for each candidate, and then choose the cell lineage that requires the least marker insertions. If the number of cells is large, we can use clustering method in which a pair of cells with the highest correlation in marker labelling are merged sequentially. The efficiency of the clustering method in estimating the correct cell lineage is confirmed by computer simulations. Finally, the clustering method is applied to reconstruct the cell lineage of ascidian from experimental data.     

Wnt and FGF signals interact to coordinate growth with cell fate specification during limb development

A fundamental question in developmental biology is how does an undifferentiated field of cells acquire spatial pattern and undergo coordinated differentiation? The development of the vertebrate limb is an important paradigm for understanding these processes. The skeletal and connective tissues of the developing limb all derive from a population of multipotent progenitor cells located in its distal tip. During limb outgrowth, these progenitors segregate into a chondrogenic lineage, located in the center of the limb bud, and soft connective tissue lineages located in its periphery. We report that the interplay of two families of signaling proteins, fibroblast growth factors (FGFs) and Wnts, coordinate the growth of the multipotent progenitor cells with their simultaneous segregation into these lineages. FGF and Wnt signals act together to synergistically promote proliferation while maintaining the cells in an undifferentiated, multipotent state, but act separately to determine cell lineage specification. Withdrawal of both signals results in cell cycle withdrawal and chondrogenic differentiation. Continued exposure to Wnt, however, maintains proliferation and re-specifies the cells towards the soft connective tissue lineages. We have identified target genes that are synergistically regulated by Wnts and FGFs, and show how these factors actively suppress differentiation and promote growth. Finally, we show how the spatial restriction of Wnt and FGF signals to the limb ectoderm, and to a specialized region of it, the apical ectodermal ridge, controls the distribution of cell behaviors within the growing limb, and guides the proper spatial organization of the differentiating tissues.     

A missense mutation (Q279R) in the Fumarylacetoacetate Hydrolase gene, responsible for hereditary tyrosinemia, acts as a splicing mutation

Background  

Tyrosinemia type I, the most severe disease of the tyrosine catabolic pathway is caused by a deficiency in fumarylacetoacetate hydrolase (FAH). A patient showing few of the symptoms associated with the disease, was found to be a compound heterozygote for a splice mutation, IVS6-1g->t, and a putative missense mutation, Q279R. Analysis of FAH expression in liver sections obtained after resection for hepatocellular carcinoma revealed a mosaic pattern of expression. No FAH was found in tumor regions while a healthy region contained enzyme-expressing nodules.     

Correlation between pulsed electromagnetic fields exposure time and cell proliferation increase in human osteosarcoma cell lines and human normal osteoblast cells in vitro

We have exposed cultured bone cells to a pulsed electromagnetic field (PEMF) for different times to find the minimal exposure time necessary to stimulate an increase of DNA synthesis. We used two different human osteosarcoma cell lines, TE-85 and MG-63, and human normal osteoblast cell (NHOC) obtained from surgical bone specimens. The cells were placed in multiwell plates and set in a tissue culture incubator between a pair of Helmoltz coils powered by a pulse generator (1.3-ms pulse, repeated at 75 Hz) for different periods of time. [3H]Thymidine incorporation was used to evaluate cell proliferation. The two osteosarcoma cell lines increase their thymidine incorporation when exposed to a PEMF for at least 30 min, both in a medium containing 10% fetal calf serum and in a serum-free medium. NHOC are known to increase their cell proliferation when exposed to PEMF but only if cultured in the presence of 10% fetal calf serum. In this experimental condition, three of the four cell lineages studied required at least 9 h of PEMF exposure to increase their DNA synthesis, whereas one cell lineage increased its cell proliferation after 6 h of PEMF exposure. Our observations confirm the hypothesis that the proliferative responses of NHOC and human osteosarcoma cell lines to PEMF exposure are quite different. Moreover, NHOC required minimal exposure times to PEMF to increase their cell proliferation, similar to that needed to stimulate bone formation in vivo.     

Is the extent of the proliferation of component cell lineages critical during organ morphogenesis?

Shoot meristems of higher plants are composed of several clonally distinct cell lineages. Periclinal chimeras have been used to determine the fate of derivatives of these lineages in mature leaves and other organs of the plant. Fates of individual meristem cells are not rigidly fixed and the distribution of tissue derived from each meristem lineage in different regions of an organ is variable. The amount of proliferation from an individual lineage can be altered without affecting the overall morphology of organs. Mechanisms exist by which cells from several lineages coordinate their relative amounts of proliferation. The conclusion from these studies is that cell proliferation and organ morphogenesis are developmental events that can be uncoupled.     

Altered transferrin gene expression in preneoplastic and neoplastic liver lesions induced in rats with N-nitrosomorpholine

The expression of the gene for the iron transport protein transferrin was found to be altered in preneoplastic and neoplastic lesions induced in the rat liver by N-nitrosomorpholine. The total RNA of ten hepatocellular carcinomas (HCC) was investigated by Northern blot analysis using a cDNA-probe comprising 150 bp of the 3′ region and compared with the total hepatic RNA in untreated rats. Seven hepatocellular carcinomas showed slight or pronounced reduction in transferrin expression. In situ hybridization of two additional hepatocellular carcinomas revealed marked reduction in the mRNA level for the transferrin gene compared with the surrounding tissue. In contrast, the majority of early preneoplastic lesions storing excess glycogen and tigroid cell foci expressed increased levels of transferrin mRNA. The loss of glycogen in mixed cell foci, which represent a later stage of hepatocarcinogenesis, was usually accompanied by a decrease in transferrin mRNA suggesting a close relationship between this change in gene expression and cellular dedifferentiation emerging during hepatocarcinogenesis.     

Altered transferrin gene expression in preneoplastic and neoplastic liver lesions induced in rats with N-nitrosomorpholine.

The expression of the gene for the iron transport protein transferrin was found to be altered in preneoplastic and neoplastic lesions induced in the rat liver by N-nitrosomorpholine. The total RNA of ten hepatocellular carcinomas (HCC) was investigated by Northern blot analysis using a cDNA-probe comprising 150 bp of the 3' region and compared with the total hepatic RNA in untreated rats. Seven hepatocellular carcinomas showed slight or pronounced reduction in transferrin expression. In situ hybridization of two additional hepatocellular carcinomas revealed marked reduction in the mRNA level for the transferrin gene compared with the surrounding tissue. In contrast, the majority of early preneoplastic lesions storing excess glycogen and tigroid cell foci expressed increased levels of transferrin mRNA. The loss of glycogen in mixed cell foci, which represent a later stage of hepatocarcinogenesis, was usually accompanied by a decrease in transferrin mRNA suggesting a close relationship between this change in gene expression and cellular dedifferentiation emerging during hepatocarcinogenesis.     

The postembryonic cell lineages of the hermaphrodite and male gonads in Caenorhabditis elegans

The ancestry of the cells in the hermaphrodite and male gonadal somatic structures of C. elegans has been traced from the two gonadal somatic progenitor cells (Z1 and Z4) that are present in the newly hatched larvae of both sexes. The lineages of Z1 and Z4 are essentially invariant. In hermaphrodites, they give rise to a symmetrical group of structures consisting of 143 cells, and in males, they give rise to an asymmetrical group of structures consisting of 56 cells. The male gonad can be distinguished from the hermaphrodite gonad soon after the first division of Z1 and Z4. However, the development of Z1 and Z4 in hermaphrodites shares several features in common with their development in males suggesting that the two programs are controlled by similar mechanisms. In the hermaphrodite lineage, a variability in the positions of two cells is correlated with a variability in the lineages of four cells. This variability suggests that cell-cell interaction may play a more significant role in organisms that develop by invariant lineages than has hitherto been considered. None of the somatic structures (e.g., uterus, spermatheca, vas deferens) develops as a clone of a single cell. Instead, cells that arise early in the Z1–Z4 lineage generally contribute descendants to more than one structure, and individual structures consist of descendants of more than one lineage.     

The embryonic cell lineage of the nematode Rhabditophanes sp

One of the unique features of the model organism Caenorhabditis elegans is its invariant development, where a stereotyped cell lineage generates a fixed number of cells with a fixed cell type. It remains unclear how embryonic development evolved within the nematodes to give rise to the complex, invariant cell lineage of C. elegans. Therefore, we determined the embryonic cell lineage of the nematode, Rhabditophanes sp. (family Alloionematidae) and made detailed cell-by-cell comparison with the known cell lineages of C. elegans, Pellioditis marina and Halicephalobus gingivalis. This gave us a unique data set of four embryonic cell lineages, which allowed a detailed comparison between these cell lineages at the level of each individual cell. This lineage comparison revealed a similar complex polyclonal fate distribution in all four nematode species (85% of the cells have the same fate). It is striking that there is a conservation of a 'C. elegans' like polyclonal cell lineage with strong left-right asymmetry. We propose that an early symmetry-breaking event in nematodes of clade IV-V is a major developmental constraint which shapes their asymmetric cell lineage.     

Flow karyology of serially cultured Chinese hamster cell lineages

Flow karyology of serially cultured Chinese hamster cell lineages has been observed to be influenced by the degree of cellular heterogeneity in culture. The minimum coefficient of variation (CV) and debris fraction obtainable vary as a cell lineage evolves from a primary cell culture to an established cell line. The cell lineages pass through a stage of decreased cellular heterogeneity from which flow karyotypes can be obtained with lower CV and debris fraction. The influence of cellular heterogeneity on flow karyology is observed with constant preparative protocol and constant instrument performance, and can be an additional source of variability.     

Two cell lineages, myf5 and myf5-independent, participate in mouse skeletal myogenesis

In skeletal muscle development, the myogenic regulatory factors myf5 and myoD play redundant roles in the specification and maintenance of myoblasts, whereas myf6 has a downstream role in differentiating myocytes and myofibers. It is not clear whether the redundancy between myf5 and myoD is within the same cell lineage or between distinct lineages. Using lineage tracing and conditional cell ablation in mice, we demonstrate the existence of two distinct lineages in myogenesis: a myf5 lineage and a myf5-independent lineage. Ablating the myf5 lineage is compatible with myogenesis sustained by myf5-independent, myoD-expressing myoblasts, whereas ablation of the myf6 lineage leads to an absence of all differentiated myofibers, although early myogenesis appears to be unaffected. We also demonstrate here the existence of a significant myf5 lineage within ribs that has an important role in rib development, suggested by severe rib defects upon ablating the myf5 lineage.     

Predominant regeneration of B-cell lineage, instead of myeloid lineage, of the bone marrow after 1 Gy whole-body irradiation in mice: role of differential cytokine expression between B-cell stimulation by IL10, Flt3 ligand and IL7 and myeloid suppression by GM-CSF and SCF

Irradiation of mice at doses of 1-1.5 Gy induced a predominant regeneration of the B-cell lineage but suppressed the regeneration of the myeloid lineage. The mechanisms underlying such reciprocal regulation of regeneration and the relationship between the two lineages remain unclear. Because the predominant regeneration of the B-cell lineage observed is considered to depend on the stromal cell function, and because the impairment of such stromal function may nullify such reciprocal responses, mouse models of senescent stromal cell impairment (SCI) and the less senescent stage of SCI (non-SCI) were compared to elucidate the mechanisms underlying the reciprocal regulation of both lineages after radiation exposure. In non-SCI mice irradiated with 1 Gy, the numbers of B-lymphocyte progenitor (CFU-preB) and granulocyte-macrophage progenitor (CFU-GM) cells in the bone marrow decreased rapidly during the first 24 h. Then the number of CFU-preB cells in the bone marrow promptly recovered from the nadir and exceeded the pretreatment level, whereas that of CFU-GM cells remained lower than the pretreatment level. The expression of genes encoding positive regulators of the B-lymphoid lineage [interleukin (IL)10, Flt3 ligand and IL7] was up-regulated; in contrast, expression of the positive regulators of the myeloid lineage [granulocyte macrophage colony-stimulating factor (GM-CSF) and stem cell factor (SCF)] was down-regulated. In SCI mice irradiated with 1 Gy, the oscillatory changes in the numbers of femoral CFU-preB and CFU-GM cells and in the expression levels of cytokine genes were less marked than those in the non-SCI mice. These results thus imply that the reciprocal regeneration depends on the up-regulation of IL10, Flt3 ligand and IL7 expression and the down-regulation of GM-CSF and SCF expression in the bone marrow, possibly depending on the hematopoietic microenvironment.