Cell division cycle genes
verse transcriptase) in vitro. If the RNA template has been processed to remove the introns, the cDNA will be much shorter than the gene from which the RNA was transcribed. The single-stranded, cDNA molecule may subsequently serve as a template for a DNA polymerase.
The symbol cDNA is some- times also applied to the double-stranded DNA mol- ecule that results. See posttranscriptional processing. cDNA clone a duplex DNA sequence complemen- tary to an RNA molecule of interest, carried in a cloning vector. cDNA library a collection of cDNA (q.v.) mole- cules, representative of all the various mRNA mole- cules produced by a specific type of cell of a given species, spliced into a corresponding collection of cloning vectors such as plasmids or lambda phages.
Since not all genes are active in every cell, a cDNA library is usually much smaller than a gene library (q.v.). If it is known which type of cell makes the desired protein (e.g., only pancreatic cells make in- sulin), screening the cDNA library from such cells for the gene of interest is a much easier task than screening a gene library. CD3 proteins See T lymphocyte. Ceboidea the superfamily containing the monkeys of Central and South America. cecidogen a gall-forming substance.
Celera Genomics a company founded by J. Craig Venter, who served as its president from 1998 to 2002. Its initial task was to complete the sequence and assembly of the human genome. A factory was set up in Rockville, MD, where 300 automated DNA sequencing machines were kept in continuous operation along with advanced computer systems for assembly of the sequenced fragments. As a test of its capabilities, Celera collaborated with the Berkeley Drosophila Genome Project to sequence and assem- ble the Drosophila genome. This task was completed during 1999 in only four months.
The first rough draft of the human genome was completed in 2000, and the event was announced in a ceremony held at the White House. At first, Celera made money by charging subscription fees for the genomic data it uncovered. However, in May of 2005, Celera closed its subscription service and released all its genomic data to the public. See Appendix C, 2000, Adams et al.; 2001, Collins and Venter et al.; Appendix E, Individual databases; DNA sequencers, Human Ge- nome Project, Mus musculus, TIGR. cell the smallest, membrane-bound protoplasmic body capable of independent reproduction.
See Ap- pendix C, 1665, Hooke. cell affinity a property of eukaryotic cells of the same type to adhere to one another but not to those of a different type; this property is lost when the cell transforms to the cancerous state. cell-cell adhesion molecules (CAMs) molecules that are responsible for the selective adhesion of cells to form specific tissues during the early em- bryogenesis of vertebrates. The cadherins (q.v.) are an example of CAMs that require Ca2+ for their functioning. cell culture a term used to denote the growing cells in vitro, including the culturing of single cells. In cell cultures the cells are not organized into tis- sues.
See Appendix C, 1940, Earle; 1956, Puck et al. cell cycle the sequence of events between one mi- totic division and another in a eukaryotic cell. Mito- (M phase) is followed by a growth (G1) phase, then by DNA synthesis (S phase), then by another growth (G2) phase, and finally by another mitosis. In HeLa cells (q.v.), for example, the G1, S, G2, and M phases take 8.2, 6.2, 4.6, and 0.6 hours, respectively. The period between mitoses (G1 + S + G2) is called interphase. Cells may have different doubling times, depending on their developmental stage or tissue type. The variation in doubling times is usually a function of the time spent in G1.
When a cell differ- entiates, it leaves the cycle and enters a phase desig- nated G0. Such “resting” cells are mitotically quies- cent, but metabolically active. See Appendix C, 1953, Howard and Pelc; centriole, checkpoint, cyclins, mat- uration promoting factor (MPF). cell determination an event in embryogenesis that specifies the developmental pathway that a cell will follow.
cell differentiation the process whereby descen- dants of a single cell achieve and maintain specializa- tions of structure and function. Differentiation pre- sumably is the result of differential transcriptions. cell division the process (binary fission in prokary- otes, mitosis in eukaryotes) by which two daughter cells are produced from one parent cell. See Appen- dix C, 1875, Strasburger.
cell division cycle genes genes first isolated from yeast which encode proteins that control critical steps in the cell division cycle. An example of such a protein is Cdc 14, a phosphatase that is localized in the nucleolus (q.v.). When the contents of the nu- cleolus are dispersed in late anaphase, this enzyme digests mitotic cyclins. See Appendix C, 1973, Hart- well et al.; cyclins.
Cell division cycle kinases
cell division cycle kinases See cyclins.. cell-driven viral transformation a method for. creating immortalized human antibody-producing. cells in vitro without forming a hybridoma (q.v.).. Normal B lymphocytes from an immunized donor. are mixed with other cells infected with the Epstein-. Barr virus (q.v.). The virus enters the B lympho-. cytes. The cells originally infected with the virus are. experimentally destroyed, and the virally trans-. formed cells producing the antibody of interest are. isolated. In cell-driven viral transformation, about 1. in 50 B lymphocytes is transformed, whereas with.
the cell hybridization technique only about 1 human. cell in 10 million is transformed.. cell fate the developmental destiny of a cell in. terms of the differentiated structure(s) that it will. inevitably give rise to during normal development.. cell fractionation the separation of the various. components of cells after homogenization of a tissue. and differential centrifugation. Four fractions are. generally obtained: (1) the nuclear fraction, (2) the. mitochondrial fraction, (3) the microsomal fraction,. and (4) the soluble fraction or cytosol. See Appendix. C, 1946, Claude.. cell-free extract a fluid obtained by rupturing cells.
and removing the particulate material, membranes,. and remaining intact cells. The extract contains most. of the soluble molecules of the cell. The preparation. of cell-free extracts in which proteins and nucleic. acids are synthesized represent milestones in bio-. chemical research. See Appendix C, 1955, Hoagland;. 1961, Nirenberg and Matthaei; 1973, Roberts and. Preston.. cell fusion the experimental formation of a single. hybrid cell with nuclei and cytoplasm from different. somatic cells. The cells that are fused may come. from tissue cultures derived from different species..
Such fusions are facilitated by the adsorption of cer-. tain viruses by the cells. See polyethylene glycol, Sen-. dai virus, Zimmermann cell fusion.. cell hybridization the production of viable hybrid. somatic cells following experimentally induced cell. fusion (q.v.). In the case of interspecific hybrids,. there is a selective elimination of chromosomes be-. longing to one species during subsequent mitoses.. Eventually, cell lines can be produced containing a. complete set of chromosomes from one species and. a single chromosome from the other. By studying. the new gene products synthesized by the hybrid.
cell line, genes residing in the single chromosome. can be identified. See Appendix C, 1960, Barski et al.,. HAT medium, hybridoma, syntenic genes.. . cell interaction genes a term sometimes used to. refer to some genes in the I region of the mouse H2. complex that influence the ability of various cellular. components of the immune system to cooperate ef-. fectively in an immune response.. cell line a heterogeneous group of cells derived. from a primary culture (q.v.) at the time of the first. transfer. See isologous cell line.. cell lineage a pedigree of the cells produced from.
an ancestral cell by binary fission in prokaryotes or. mitotic division in eukaryotes. Caenorhabditis eleg-. ans (q.v.) is the only multicellular eukaryote for. which the complete pattern of cell divisions from. single-celled zygote to mature adult has been eluci-. dated. Cell lineage diagrams are available that detail. each cell or nuclear division and the fate of each cell. produced by a terminal division.. cell lineage mutants mutations that affect the di-. vision of cells or the fates of their progeny cells. Cell. lineage mutants generally fall into two broad classes.. The first contains mutations that affect general cellu-.
lar processes, such as cell division or DNA replica-. tion. Mutants perturbing the cell division cycle have. been analyzed most extensively in Saccharomyces. cerevisiae. The second class of mutations shows a. striking specificity in their effects. For example, cell. lineage mutants are known in Caenorhabditis elegans. where particular cells are transformed to generate. lineages or to adopt differentiated fates characteris-. tic of cells normally found in different positions, at. different times, or in the opposite sex. Some of these. mutants result from transformations in cell fates. For. example, a particular cell “A” will adopt the fate of. another cell “B,” and this results in the loss of the. cells normally generated by A and the duplication of. cells normally generated by B. Such transformations.
resemble the homeotic mutations (q.v.) of Drosoph-. ila. In Caenorhabditis, mutations of this type are. generally symbolized by lin. See Appendix C, 1983,. Greenwald et al.; developmental control genes, het-. erochronic mutations, selector genes.. cell lysis disruption of the cell membrane, allow-. ing the dissolution of the cell and exposure of its. contents to the environment. Examples: bacteria un-. dergo bacteriolysis, red blood cells experience hemol-. ysis.. cell-mediated immunity immune responses pro-. duced by T lymphocytes rather than by immuno-. globulins (humoral- or antibody-mediated immu-. nity); abbreviated CMI.. .