Chromosomal engineering

Artificial chromosomes (ACs) are engineered chromosomes with defined genetic contents that can function as non-integrating vectors with large carrying capacity and stability. The large carrying capacity allows the engineering of ACs with multiple copies of the same transgene, gene complexes, and to include regulatory elements necessary for the regulated expression of transgene(s). Artificial chromosome based systems are composed of AC engineered to harbor and express gene(s) of interest and an appropriate recombination system for 'custom' engineering of ACs. These systems have the potential to become an efficient tool in diverse gene technology applications such as cellular protein manufacturing, transgenic animal production, and ultimately gene therapy. Recent advances in artificial chromosome technologies outline the value of these systems and justify the future research efforts to overcome the obstacles in exploring their full capabilities.     

Chromosomal transplantation

Dissociated cells of middle-to-late blastulae were exposed to 0.1 mg colchicine/ml and achieved 92% metaphase arrest. These cells contained a haploid set of Bombina maxima (Anura:Discoglossidae) chromosomes. When transplanted into the enucleated eggs of B. orientalis, some donor cells stimulated development to the late blastula and middle gastrula stages. — Most (17/20) of the embryos resulting from chromosomal transplantation were nonmosaic aneuploids. A high percentage of recipient egg enucleation (93%), the ratio of long-to-short chromosomes, and the presence of species-specific marker chromosomes proved that chromosomes were transplanted from the donor cells. Therefore, metaphase chromosomes lacking intact spindle apparatuses were injected into and incorporated by amphibian eggs. These chromosomes were replicated in all cells of the resulting embryos. The aneuploidy of these embryos is explained by an inability of the recipient egg to locate and replicate many transplanted chromosomes (44%) before first cleavage.     

Chromosomal character optimization

A method is presented to optimize chromosomal data on a cladogram. This procedure simultaneously considers variation at the nucleotide and locus levels including nucleotide substitution, insertion and deletion, locus insertions and deletion, and gene rearrangement. Locus labeling is not a requirement of the procedure and such annotation will result from the dynamic homology analysis of the chromosome data. An example of complete arthropod mtDNA sequences is presented.     

Chromosomal evolution withinPiperaceae

Chromosome numbers for 26 different species of the generaPiper, Peperomia andPothomorphe (Piperaceae) are reported. The basic chromosome numbers are 2n = 26, x = 13 (Piper, Pothomorphe) and 2n = 22, x = 11 (Peperomia), polyploid series are characteristic forPiper andPeperomia. Piper has the smallest chromosomes and prochromosomal interphase nuclei,Peperomia the largest ones and mostly reticulate to euchromatic nuclei.Pothomorphe is intermediate in both characters. The karyomorphological differences betweenPothomorphe andPiper underline their generic separation. Interspecific size variation of chromosomes occurs inPiper andPeperomia. Infraspecific polyploidy was observed inPiper betle. C-banding reveals different patterns of heterochromatin (hc) distribution between the genera investigated. The genome evolution is discussed.     

Chromosomal evolution inCallithrix emiliae

We studied the karyotype of specimens ofCallithrix emiliae (Callithricidae, Primates) from Rondonia, Brazil. Comparison with the karyotype ofCallithrix jacchus showed that, even though these two species show many karyotypic similarities, they differ by a Robertsonian translocation, a paracentric inversion and large-scale addition of heterochromatin. TheC. emiliae species appears to be in an active phase of chromosome evolution by the addition of constitutive heterochromatin.     

Chromosomal translocations in cancer

Genetic alterations in DNA can lead to cancer when it is present in proto-oncogenes, tumor suppressor genes, DNA repair genes etc. Examples of such alterations include deletions, inversions and chromosomal translocations. Among these rearrangements chromosomal translocations are considered as the primary cause for many cancers including lymphoma, leukemia and some solid tumors. Chromosomal translocations in certain cases can result either in the fusion of genes or in bringing genes close to enhancer or promoter elements, hence leading to their altered expression. Moreover, chromosomal translocations are used as diagnostic markers for cancer and its therapeutics. In the first part of this review, we summarize the well-studied chromosomal translocations in cancer. Although the mechanism of formation of most of these translocations is still unclear, in the second part we discuss the recent advances in this area of research.     

Chromosomal proteins of conifers

During imbibition and germination of jack pine seeds, the composition of the total extractable chromatin varied. Relative to DNA, the histone levels decreased as the nonhistone chromosomal proteins (NHCP) increased. New chromosomal proteins were synthesized after 2 days of imbibition as judged by recovery of ¹⁴C-amino acids from the major protein fractions. Phosphorylation of histones from ³²P-phosphoric acid was detected before the incorporation of ¹⁴C-amino acids. In the seed the synthesis and relative changes of chromatin coincided with a fall in total soluble protein and free arginine N. By contrast, adenylate energy charge, free glutamine N and in vitro template activity of chromatin increased during chromatin protein synthesis. When seeds had germinated for 4 days after the start of imbibition more radioactivity, derived from free ¹⁴C-amino acids, was recovered from the NHCP than from the histones. The percentage amino acid composition of most histone fractions remained stable, whereas the composition of NHCP changed more with time. The phosphorylation of NHCP was 8- to 41-fold greater than that of the histones. Phosphorylation of histone H4 was not detected at any stage of germination. Correlations between recovery of radioactivity (³²P and ¹⁴C) from chromosomal proteins and higher adenylate energy charge were positive.     

Chromosomal evolution in prosimians

A cytogenetic study of almost all the Malagasy lemurs, of several representative Lorisiforms and one representative each of Tupaiiforms and Tarsiforms is reported. A phylogenic tree was constructed for all species exceptTarsius syrichta, which could not be related to either Prosimians or Simians. Three branches emerge, independentely or after a short common trunk, from the ancestral karyotype of all the Primates. One branch leads to the Lorisiforms, another to the Lemuriforms and the third to the Tupaïa. The chromosomal evolution of the Lorisiforms which gave rise to the Galagidae and the Lorisidae is of a populational mode, while among the Lemuriforms 4 modes of speciation have occurred: populational for the Indriidae, dichotomic for the Lepilemuridae, bushy for the Lemuridae and a catenary one for the Hapelemurs.