Recombinant bacteriophage A from a human ge- nomic library were screened to identify human DNA inserts hav- ing only unique sequences. Unique human inserts were found in about 1% of the phage screened. One recombinant phage, P3-2, was studied in detail. It contains a human insert of 14.7 kilobases with four internal EcoRI cleavage sites. A restriction map was con- structed for EcoRI and BamHI sites. Hybridization of the 32P-la- beled P3-2 probe to a Southern blot of EcoRI-digested total human DNA yielded distinct bands at positions corresponding to the hu- man insert fragments contained in P3-2. By using a series of hu- man-Chinese hamster somatic cell hybrids containing unique combinations of human chromosomes, the human DNA segment in phage P3-2 was assigned to human chromosome. 22 by blot hy- bridization and synteny analysis. In addition, another human DNA segment, 11.4 kilobases, in phage P3-10 was assigned to human chromosome 10 by similar procedures. With this approach, more unique DNA sequences can be isolated, assigned to specific human chromosomes, and used as genetic markers for gene mapping and linkage, polymorphism, and other genetic studies in the human genome.
Progesterone is involved in the development and progression of breast cancers, and progesterone receptors (PR) are important markers of hormone dependence and disease prognosis. We have used a human PR cDNA probe, genomic DNA blotting of a series of Chinese hamster-human cell hybrids, and in situ hybridization to map the human PR gene to chromosome 11, band q13. This band also contains the human homolog of the mouse mammary tumor virus integration site, int-2, which surrounds a protooncogene thought to be involved in the development of murine mammary cancers. That these two genes share the same chromosomal location raises important questions about their possible linkage and about the relationship between the mammary-specific oncogene and the steroid hormone in the development, growth, and hormone dependence of human breast cancers.
ABSTRACT Enolase-2 (ENO2), previously termed 14-3-2 protein, is an isozyme of enolase that is enriched in neuronal tissue. The gene coding for ENO2 was previously assigned to human chromosome 12. The present study presents data for a regional mapping of gene ENO2 using cell hybrids containing various deletions of human chromosome 12. These deletions were produced by treatment with chromosome-breaking agents. Cytogenetic analysis has allowed assignment of ENO2 to the short arm of chromosome 12, in the region of pter-pizos. This assignment is consistent with the segregation pattern of the 93 hybrid clones analysed. The segregation pattern has also established the linear order of 6 genes on chromosome 12: pter — TPI — GAPD — LDHB — ENO2— centromere — SHMT — PEPB — qter. Estimation of the relative distances between the 6 genes on chromosome 12 has been made by a statistical mapping analysis of the segregation data of the hybrid clones. A set of deletion hybrids containing various combinations of these 6 markers has been established for a rapid regional mapping of genes in one of these regions on chromosome 12.
In contrast to the distal half of the long arm of chromosome 21, the proximal half of approximately 20 megabases of DNA, including 21q11–21 bands, is low in GC content, CpG islands, and identified genes. Despite intensive searches, very few genes and cDNAs have been found in this region. Since the 21q11–21 region is associated with certain Down syndrome pathologies like mental retardation, the identification of relevant genes in this region is important. We used a different approach by constructing microdissection libraries specifically for this region and isolating unique sequence microclones for detailed molecular analysis. We found that this region is enriched with middle and low-copy repetitive sequences, and is also heavily methylated. By sequencing and homology analysis, we identified a significant number of genes/cDNAs, most of which appear to belong to gene families. In addition, we used unique sequence microclones in direct screening of cDNA libraries and isolated 12 cDNAs for this region. Thus, although the 21q11–21 region is gene poor, it is not completely devoid of genes/cDNAs. The presence of high proportions of middle and low-copy repetitive sequences in this region may have evolutionary significance in the genome organization and function of this region. Since 21q11–21 is heavily methylated, the expression of genes in this region may be regulated by a delicate balance of methylation and demethylation, and the presence of an additional copy of chromosome 21 may seriously disturb this balance and cause specific Down syndrome anomalies including mental retardation.
