Parity and breastfeeding are protective against breast cancer in Nigerian women.

As the relation between reproductive factors and breast cancer risk has not been systematically studied in indigenous women of sub-Saharan Africa, we examined this in a case-control study in Nigeria. In-person interviews were conducted using structured questionnaires to collect detailed reproductive history in 819 breast cancer cases and 569 community controls between 1998 and 2006. Logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CI). Compared with women with menarcheal age<17 years, the adjusted OR for women with menarcheal age>or=17 years was 0.72 (95% CI: 0.54-0.95, P=0.02). Parity was negatively associated with risk (P-trend=0.02) but age at first live birth was not significant (P=0.16). Importantly, breast cancer risk decreased by 7% for every 12 months of breastfeeding (P-trend=0.005). It is worth noting that the distribution of reproductive risk factors changed significantly from early to late birth cohorts in the direction of increasing breast cancer incidence. Our findings also highlight the heterogeneity of breast cancer aetiology across populations, and indicate the need for further studies among indigenous sub-Saharan women.

Male breast cancer in Cowden syndrome patients with germline PTEN mutations.

Cowden syndrome (CS) (OMIM 158350) is a multiple hamartoma syndrome associated with germline mutations in the PTEN tumour suppressor gene. While CS is characterised most commonly by non-cancerous lesions (mucocutaneous trichilemmomas, acral and palmoplantar keratoses, and papillomatous papules), it is also associated with an increased susceptibility to breast cancer (in females) and thyroid cancer, as well as non-cancerous conditions of the breast and thyroid. Here we report two cases of male breast cancer occurring in patients with classical CS phenotypes and germline PTEN mutations. The first subject was diagnosed with CS indicated primarily by mucocutaneous papillomatosis, facial trichilemmomas, and macrocephaly with frontal bossing at the age of 31 years. He developed breast cancer at 41 years and subsequently died of the disease. A PTEN mutation, c.802delG, was identified in this subject, yet none of his family members showed evidence of a CS phenotype, suggesting that this PTEN mutation may be a de novo occurrence. The second subject had a CS phenotype including multiple trichilemmomas and thyroid adenoma, developed male breast cancer at 43 years, and died of the disease at 57 years. He was a carrier of a PTEN mutation c.347-351delACAAT that cosegregated with the CS phenotype in affected family members. These two cases of male breast cancer associated with germline PTEN mutations and the CS phenotype suggest that CS may be associated with an increased risk of early onset male as well as female breast cancer.

Prevalence of BRCA1 and BRCA2 mutations among clinic-based African American families with breast cancer.

To define the prevalence and relative contributions of BRCA1 and BRCA2 mutations among African American families with breast cancer, we analyzed 28 DNA samples from patients identified through two oncology clinics. The entire coding regions of BRCA1 and BRCA2 were screened by protein truncation test, heteroduplex analysis, or single-stranded conformation polymorphism followed by DNA sequencing of variant bands. Deleterious protein-truncating BRCA1 and BRCA2 mutations were identified in five patients or 18% of the entire cohort. Only 8% (1 of 13) of women with a family history of breast cancer, but no ovarian cancer, had mutations. The mutation rates were higher for women from families with a history of breast cancer and at least one ovarian cancer (three of six, 50%). One woman with a family history of undocumented cancers was also found to carry a deleterious mutation in BRCA2. The spectrum of mutations was unique in that one novel BRCA1 mutation (1625del5) and three novel BRCA2 mutations (1536del4, 6696delTC, and 7795delCT) were identified. No recurrent mutations were identified in this cohort, although one BRCA2 (2816insA) mutation had been previously reported. In addition, two BRCA1 and four BRCA2 missense mutations of unknown significance were identified, one of which was novel. Taken together with our previous report on recurrent mutations seen in unrelated families, we conclude that African Americans have a unique mutation spectrum in BRCA1 and BRCA2 genes, but recurrent mutations are likely to be more widely dispersed and therefore not readily identifiable in this population.

Microtubule architecture specified by a beta-tubulin isoform.

In Drosophila melanogaster, a testis-specific beta-tubulin (beta2) is required for spermatogenesis. A sequence motif was identified in carboxyl termini of axonemal beta-tubulins in diverse taxa. As a test of whether orthologous beta-tubulins from different species are functionally equivalent, the moth Heliothis virescens beta2 homolog was expressed in Drosophila testes. When coexpressed with beta2, the moth isoform imposed the 16-protofilament structure characteristic of that found in the moth on the corresponding subset of Drosophila microtubules, which normally contain only 13-protofilament microtubules. Thus, the architecture of the microtubule cytoskeleton can be directed by a component beta-tubulin.

Structural analysis of mutations in the Drosophila beta 2-tubulin isoform reveals regions in the beta-tubulin molecular required for general and for tissue-specific microtubule functions.

We have determined the lesions in a number of mutant alleles of beta Tub85D, the gene that encodes the testis-specific beta 2-tubulin isoform in Drosophila melanogaster. Mutations responsible for different classes of functional phenotypes are distributed throughout the beta 2-tubulin molecule. There is a telling correlation between the degree of phylogenetic conservation of the altered residues and the number of different microtubule categories disrupted by the lesions. The majority of lesions occur at positions that are evolutionarily highly conserved in all beta-tubulins; these lesions disrupt general functions common to multiple classes of microtubules. However, a single allele B2t6 contains an amino acid substitution within an internal cluster of variable amino acids that has been identified as an isotype-defining domain in vertebrate beta-tubulins. Correspondingly, B2t6 disrupts only a subset of microtubule functions, resulting in misspecification of the morphology of the doublet microtubules of the sperm tail axoneme. We previously demonstrated that beta 3, a developmentally regulated Drosophila beta-tubulin isoform, confers the same restricted morphological phenotype in a dominant way when it is coexpressed in the testis with wild-type beta 2-tubulin. We show here by complementation analysis that beta 3 and the B2t6 product disrupt a common aspect of microtubule assembly. We therefore conclude that the amino acid sequence of the beta 2-tubulin internal variable region is required for generation of correct axoneme morphology but not for general microtubule functions. As we have previously reported, the beta 2-tubulin carboxy terminal isotype-defining domain is required for suprastructural organization of the axoneme. We demonstrate here that the beta 2 variant lacking the carboxy terminus and the B2t6 variant complement each other for mild-to-moderate meiotic defects but do not complement for proper axonemal morphology. Our results are consistent with the hypothesis drawn from comparisons of vertebrate beta-tubulins that the two isotype-defining domains interact in a three-dimensional structure in wild-type beta-tubulins. We propose that the integrity of this structure in the Drosophila testis beta 2-tubulin isoform is required for proper axoneme assembly but not necessarily for general microtubule functions. On the basis of our observations we present a model for regulation of axoneme microtubule morphology as a function of tubulin assembly kinetics.

Tissue-specific microtubule functions in Drosophila spermatogenesis require the beta 2-tubulin isotype-specific carboxy terminus.

beta-Tubulins are encoded by members of multigene families and are generally highly conserved at the sequence level. The carboxyl terminal 15 amino acids are markedly more diverged than the rest of the sequence and constitute an "isotype defining region," which is conserved in corresponding beta-tubulin isoforms in different vertebrate species. It is thought that the carboxy terminus of beta-tubulin may not be required for assembly of microtubules per se, but it may be necessary for conferring properties on beta-tubulins required for isotype-specific functions. We have determined the extent to which a beta-tubulin isoform that lacks its carboxy terminus can assemble into functional suprastructures by generating two early-stop-codon variants of the gene for the testis-specific beta-tubulin (beta 2) in Drosophila melanogaster. We have also sequenced the null allele of this gene and discovered that it also contains an early-stop codon. By examining the products of these genes and the phenotypes they confer, we have determined that the beta-tubulin variants with large truncations (171 or 50 amino acids) do not accumulate to detectable levels and provide no beta-tubulin function. However, a small truncation missing only the terminal 15 amino acids is capable of being assembled into ultrastructurally normal looking microtubules in vivo, even though the truncated protein is less stable than wildtype beta 2. The functional failings of this truncated beta-tubulin are manifested in defective microtubule-based spermatogenic suprastructures, rather than at the level of assembly of individual microtubules. The most remarkable defect conferred by the truncated beta 2 is the failure of axonemes to assemble with proper organization, even though microtubules with presumptive axoneme identity are clearly present. We therefore demonstrate that the carboxy terminus of beta 2-tubulin is indeed required for organization of microtubule suprastructures in spermatogenesis. This observation supports the hypothesis that the variable carboxy terminus mediates isotype-specific microtubule-dependent functions.

Molecular analysis of the swallow gene of Drosophila melanogaster.

We report the cloning and molecular characterization of the swallow gene, a maternal-effect gene of Drosophila melanogaster. Maternal-effect genes are transcribed only during oogenesis; one such gene, bicoid, encodes a message that is localized at the anterior end of oocytes, eggs, and early embryos. swallow+ activity is necessary during oogenesis for bicoid message localization. We show here that a fragment of a previously identified clone, introduced into the genome by P-element-mediated transformation, is able to rescue the maternal-effect lethality of swallow mutants, confirming the identity of this clone as swallow. By in situ hybridization, we show that swallow message is synthesized in nurse cells during oogenesis but is not localized along either the anterior-posterior or dorsal-ventral axes. We have confirmed an earlier finding that the localization of bicoid message is defective in swallow- oocytes and eggs.