INTRODUCTION One of the main questions in the field of developmental biology is how are multiple developmental cues integrated stepwise with the transcriptional regulation of cell fate decisions. To date, a large number of cis-regulatory modules (CRMs) have been identified by promoter/enhancer analyses in many organisms, and conceptual gene regulatory networks have been created for various deve...

Wdr5 is an essential component of SET/MLL methylase complexes that catalyze histone H3 lysine 4 trimethylation. The maternal Wnt/β-catenin signaling is necessary for the H3K4me3 deposition at organizer genes in early Xenopus embryos. However, it remains unknown whether any component of SET/MLL methylase complex is required for Wnt signaling to establish H3K4me3 at its targets during the organiz...

Many of the experimental observations on which the understanding of inductive interactions during vertebrate development are based were originally made using amphibian embryos (reviewed by Slack and Tannahill, 1992). In amphibians, induction of dorsal mesoderm and specification of the anteriorposterior axis begin at the time of gastrulation, in Spemann’s organizer region, in response to signals...

Cytogenetic studies were performed on two sympatric species of Characidium, C. gomesi and C. cf. zebra, from the Grande River basin, Minas Gerais State, Brazil. Although both species had a chromosome number of 50 with a karyotype exclusively consisting of metaand submetacentric chromosomes, interspecific diversity was detected concerning the size of the two first chromosome pairs of the karyoty...

We explore the extent and sources of epigenetic variation in cytosine methylation in natural accessions of the flowering plant, Arabidopsis thaliana, by focusing on the methylation of the major rRNA gene repeats at the two nucleolus organizer regions (NOR). Our findings indicate that natural variation in NOR methylation results from a combination of genetic and epigenetic mechanisms. Genetic va...

Concerted evolution is the production and maintenance of homogeneity within repeated families of DNA. Two mechanisms--unequal crossing over and biased gene conversion--have been the principal explanations of concerted evolution. Concerted evolution of ribosomal DNA (rDNA) arrays is thought to be largely the result of unequal crossing over. However, concerted evolution of rDNA in parthenogenetic...

Many students with learning disabilities (LD) experience difficulties with extracting relationships from expository text, especially if they are implicit. Results from studies with K-12 participants have been inconclusive regarding the potency of the graphic organizer (GO) as a comprehension tool. This study attempted to address some of the concerns with GO research by examining the effects of ...

Scaptotrigona xanthotricha has a wide geographic distribution in the Brazilian Atlantic rainforest. One population from southeast and two from northeast Brazil were analyzed and were found to have chromosome polymorphisms. Although the chromosome number 2n = 34 is conserved in this species, karyotypic analysis revealed clear differences between the three populations. Congruent and ubiquitous mu...

Drosophila mulleri (MU) and D. arizonae (AR) are cryptic species of the mulleri complex, mulleri subgroup, repleta group. Earlier cytogenetic studies revealed that these species have different regulatory mechanisms of nucleolar organizing activity. In these species, nucleolar organizing regions are found in both the X chromosome and the microchromosome. In the salivary glands of hybrids between...

In genetic hybrids, nucleolus formation on chromosomes inherited from only one parent is the epigenetic phenomenon, nucleolar dominance. By using Arabidopsis suecica, the allotetraploid hybrid of Arabidopsis thaliana and Arabidopsis arenosa, natural variation in nucleolar dominance was found to occur, providing a unique opportunity to examine homologous nucleolus organizer regions (NORs) in the...