Correlation of the physical and genetic maps in the lin-12 region of Caenorhabditis elegans.

We describe the assembly of a set of overlapping clones from the lin-12 III chromosomal region that spans approximately 600 kb, and the identification of two restriction fragment length polymorphisms, eP6 and eP7, that flank the lin-12 locus. A comparison of the physical map and the genetic map yields approximate measurements of 930 kb/map unit for the eP6--lin-12 interval and 830 kb/map unit for the lin-12--eP7 interval. We interpret these values as supporting the proposal that the apparent clustering of genes observed for C. elegans autosomes results from decreased recombination frequency in clusters and not from nonrandom distribution of genes on the physical map.     

Molecular Genetics of the Caenorhabditis Elegans Heterochronic Gene Lin-14

We describe a general strategy for the genetic mapping in parallel of multiple restriction fragment length polymorphism (RFLP) loci. This approach allows the systematic identification for cloning of physical genetic loci within about 100 kb of any gene in Caenorhabditis elegans. We have used this strategy of parallel RFLP mapping to clone the heterochronic gene lin-14, which controls the timing and sequence of many C. elegans postembryonic developmental events. We found that of about 400 polymorphic loci in the C. elegans genome associated with the Tc1 family of repetitive elements, six are within 0.3 map unit of lin-14. The three closest lin-14-linked Tc1-containing restriction fragments were cloned and used to identify by hybridization an 830-kb region of contiguous cloned DNA fragments assembled from cosmid and yeast artificial chromosome libraries. A lin-14 intragenic recombinant that separated a previously cryptic lin-14 semidominant mutation from a cis-acting lin-14 suppressor mutation was used to map the location of the lin-14 gene to a 25-kb region of this 830-kb contig. DNA probes from this region detected lin-14 allele-specific DNA alterations and a lin-14 mRNA. Two lin-14 semi-dominant alleles, which cause temporally inappropriate lin-14 gene activity and lead to the reiterated expression of specific early developmental events, were shown to delete sequences from the lin-14 gene and mRNA. These deletions may define cis-acting sequences responsible for the temporal regulation of lin-14.     

Image analysis of restriction enzyme fingerprint autoradiograms

A genome mapping system has been developed that reads and assemblesdata from clones analysed by restriction enzyme fragmentationand polyacrylamide gel electrophoresis. Input data for the systemcan be most effectively obtained by the use of a scanning densitometerand image-processing package, such as that described in thisarticle. The image-processing procedure involves preliminarylocation of bands, cooperative tracking of lanes by correlationof adjacent bands, a precise densitometric pass, alignment ofthe marker bands with the standard, optional interactive editing,and normalization of the accepted bands. Received on August 31, 1988; accepted on December 6, 1988     

Post-embryonic development in the ventral cord of Caenorhabditis elegans.

56 nerve cells are added to the ventral cord and associated ganglia of Caenorhabditis elegans at about the time of the first larval moult. These cells are produced by the uniform division of 13 neuroblasts followed by a defined pattern of cell deaths. Comparison with the data in the previous paper suggests that there is a relationship between the ancestry of a cell and its function. The significance of programmed cell death is discussed.     

Software for genome mapping by fingerprinting techniques

A genome mapping package has been developed for reading andassembling data from clones analysed by restriction enzyme fragmentationand polyacrylamide gel electrophoresis. The package comprises:data entry; matching; assembly; statistical analysis; modelling.Data entry can be either manual or by a semiautomatic systembased on a scanning densitometer. The primary emphasis in theanalytical routines is on flexibility and interactive convenience,so that the operator has full knowledge of and control overthe growing map, but a variety of automatic options are included.The package continually grows to meet the needs of the Caenorhabditisproject. Received on July 17, 1987; accepted on November 20, 1987     

Cell cycling and DNA replication in a mutant blocked in cell division in the nematode Caenorhabditis elegans

The postembryonic development of the nematode Caenorhabditis elegans has been described at the level of individual cell lineages. A mutant of postembryonic development, lin-5 II, causes a failure of postembryonic nuclear and cell divisions. Mitosis in living animals is seen by light microscopy to proceed through prophase and nuclear envelope breakdown, but an abnormal-looking metaphase plate forms in the mutant, after which the interphase nuclear morphology reappears until the next attempted round of division. The precursor cells which give rise to the ventral nerve cord have been studied in lin-5. In the wild type these cells divide asymmetrically to give six descendants (one hypodermal cell and five neurons). In the mutant these precursors accumulate approximately six times the diploid quantity of DNA within a single nucleus, while attempting mitosis up to three times. These polyploid cells display characteristics of the cells they would have produced ordinarily.     

Regulation and cell autonomy during postembryonic development of Caenorhabditis elegans

The role of cell-cell interaction in the postembryonic development of nongonadal tissues in the nematode Caenorhabditis elegans has been explored by selective cell ablation with a laser microbeam. Examples have been found of induction and of regulation in cell lineage and fate. Regulation in which one cell precisely or partially replaces another is seen, but only in certain groups of hypodermal cells which resemble one another closely; cells which are unique are not replaced in this way. The regulation of cell form is more widespread and less restrictive.