MUTYH Associated Polyposis (MAP)

MUTYH Associated Polyposis (MAP), a Polyposis predisposition caused by biallelic mutations in the Base Excision Repair (BER) gene MUTYH, confers a marked risk of colorectal cancer (CRC). The MAP phenotype is difficult to distinguish from other hereditary CRC syndromes. Especially from Familial Adenomatous Polyposis (FAP) and to a lesser extend Lynch Syndrome, which are caused by germline mutations in the APC and Mismatch Repair (MMR) genes, respectively.     

Truncating and missense BMPR2 mutations differentially affect the severity of heritable pulmonary arterial hypertension

Background

Autosomal dominant inheritance of germline mutations in the bone morphogenetic protein receptor type 2 (BMPR2) gene are a major risk factor for pulmonary arterial hypertension (PAH). While previous studies demonstrated a difference in severity between BMPR2 mutation carriers and noncarriers, it is likely disease severity is not equal among BMPR2 mutations. We hypothesized that patients with missense BMPR2 mutations have more severe disease than those with truncating mutations.

Methods

Testing for BMPR2 mutations was performed in 169 patients with PAH (125 with a family history of PAH and 44 with sporadic disease). Of the 106 patients with a detectable BMPR2 mutation, lymphocytes were available in 96 to functionally assess the nonsense-mediated decay pathway of RNA surveillance. Phenotypic characteristics were compared between BMPR2 mutation carriers and noncarriers, as well as between those carriers with a missense versus truncating mutation.

Results

While there was a statistically significant difference in age at diagnosis between carriers and noncarriers, subgroup analysis revealed this to be the case only for females. Among carriers, there was no difference in age at diagnosis, death, or survival according to exonic location of the BMPR2 mutation. However, patients with missense mutations had statistically significant younger ages at diagnosis and death, as well as shorter survival from diagnosis to death or lung transplantation than those with truncating mutations. Consistent with this data, the majority of missense mutations were penetrant prior to age 36 years, while the majority of truncating mutations were penetrant after age 36 years.

Conclusion

In this cohort, BMPR2 mutation carriers have more severe PAH disease than noncarriers, but this is only the case for females. Among carriers, patients with missense mutations that escape nonsense-mediated decay have more severe disease than those with truncating mutations. These findings suggest that treatment and prevention strategies directed specifically at BMPR2 pathway defects may need to vary according to the type of mutation.     

Overexpression of Gremlin-1 in Patients with Loeys-Dietz Syndrome: Implications on Pathophysiology and Early Disease Detection

Backgrounds

The Loeys-Dietz syndrome (LDS) is an inherited connective tissue disorder caused by mutations in the transforming growth factor β (TGF-β) receptors TGFBR1 or TGFBR2. Most patients with LDS develop severe aortic aneurysms resulting in early need of surgical intervention. In order to gain further insight into the pathophysiology of the disorder, we investigated circulating outgrowth endothelial cells (OEC) from the peripheral blood of LDS patients from a cohort of 23 patients including 6 patients with novel TGF-β receptor mutations.

Methods and Results

We performed gene expression profiling of OECs using microarray analysis followed by quantitative PCR for verification of gene expression. Compared to OECs of age- and sex-matched healthy controls, OECs isolated from three LDS patients displayed altered expression of several genes belonging to the TGF-β pathway, especially those affecting bone morphogenic protein (BMP) signalling including BMP2, BMP4 and BMPR1A. Gene expression of BMP antagonist Gremlin-1 (GREM1) showed the most prominent up-regulation. This increase was confirmed at the protein level by immunoblotting of LDS-OECs. In immunohistochemistry, abundant Gremlin-1 protein expression could be verified in endothelial cells as well as smooth muscle cells within the arterial media. Furthermore, Gremlin-1 plasma levels of LDS patients were significantly elevated compared to healthy control subjects.

Conclusions

These findings open new avenues in the understanding of the pathogenesis of Loeys-Dietz syndrome and the development of new diagnostic serological methods for early disease detection.     

Copy Number Variation Analysis in Familial BRCA1/2-Negative Finnish Breast and Ovarian Cancer

Background

Inherited factors predisposing individuals to breast and ovarian cancer are largely unidentified in a majority of families with hereditary breast and ovarian cancer (HBOC). We aimed to identify germline copy number variations (CNVs) contributing to HBOC susceptibility in the Finnish population.

Methods

A cohort of 84 HBOC individuals (negative for BRCA1/2-founder mutations and pre-screened for the most common breast cancer genes) and 36 healthy controls were analysed with a genome-wide SNP array. CNV-affecting genes were further studied by Gene Ontology term enrichment, pathway analyses, and database searches to reveal genes with potential for breast and ovarian cancer predisposition. CNVs that were considered to be important were validated and genotyped in 20 additional HBOC individuals (6 CNVs) and in additional healthy controls (5 CNVs) by qPCR.

Results

An intronic deletion in the EPHA3 receptor tyrosine kinase was enriched in HBOC individuals (12 of 101, 11.9%) compared with controls (27 of 432, 6.3%) (OR = 1.96; P = 0.055). EPHA3 was identified in several enriched molecular functions including receptor activity. Both a novel intronic deletion in the CSMD1 tumor suppressor gene and a homozygous intergenic deletion at 5q15 were identified in 1 of 101 (1.0%) HBOC individuals but were very rare (1 of 436, 0.2% and 1 of 899, 0.1%, respectively) in healthy controls suggesting that these variants confer disease susceptibility.

Conclusion

This study reveals new information regarding the germline CNVs that likely contribute to HBOC susceptibility in Finland. This information may be used to facilitate the genetic counselling of HBOC individuals but the preliminary results warrant additional studies of a larger study group.     

Germline mutations in BMPR1A/ALK3 cause a subset of cases of juvenile polyposis syndrome and of Cowden and Bannayan-Riley-Ruvalcaba syndromes

Juvenile polyposis syndrome (JPS) is an inherited hamartomatous-polyposis syndrome with a risk for colon cancer. JPS is a clinical diagnosis by exclusion, and, before susceptibility genes were identified, JPS could easily be confused with other inherited hamartoma syndromes, such as Bannayan-Riley-Ruvalcaba syndrome (BRRS) and Cowden syndrome (CS). Germline mutations of MADH4 (SMAD4) have been described in a variable number of probands with JPS. A series of familial and isolated European probands without MADH4 mutations were analyzed for germline mutations in BMPR1A, a member of the transforming growth-factor beta-receptor superfamily, upstream from the SMAD pathway. Overall, 10 (38%) probands were found to have germline BMPR1A mutations, 8 of which resulted in truncated receptors and 2 of which resulted in missense alterations (C124R and C376Y). Almost all available component tumors from mutation-positive cases showed loss of heterozygosity (LOH) in the BMPR1A region, whereas those from mutation-negative cases did not. One proband with CS/CS-like phenotype was also found to have a germline BMPR1A missense mutation (A338D). Thus, germline BMPR1A mutations cause a significant proportion of cases of JPS and might define a small subset of cases of CS/BRRS with specific colonic phenotype.     

Investigating the potential role of genetic and epigenetic variation of DNA methyltransferase genes in hyperplastic polyposis syndrome

Background

Hyperplastic Polyposis Syndrome (HPS) is a condition associated with multiple serrated polyps, and an increased risk of colorectal cancer (CRC). At least half of CRCs arising in HPS show a CpG island methylator phenotype (CIMP), potentially linked to aberrant DNA methyltransferase (DNMT) activity. CIMP is associated with methylation of tumor suppressor genes including regulators of DNA mismatch repair (such as MLH1, MGMT), and negative regulators of Wnt signaling (such as WIF1). In this study, we investigated the potential for interaction of genetic and epigenetic variation in DNMT genes, in the aetiology of HPS.

Methods

We utilized high resolution melting (HRM) analysis to screen 45 cases with HPS for novel sequence variants in DNMT1, DNMT3A, DNMT3B, and DNMT3L. 21 polyps from 13 patients were screened for BRAF and KRAS mutations, with assessment of promoter methylation in the DNMT1, DNMT3A, DNMT3B, DNMT3L MLH1, MGMT, and WIF1 gene promoters.

Results

No pathologic germline mutations were observed in any DNA-methyltransferase gene. However, the T allele of rs62106244 (intron 10 of DNMT1 gene) was over-represented in cases with HPS (p<0.01) compared with population controls. The DNMT1, DNMT3A and DNMT3B promoters were unmethylated in all instances. Interestingly, the DNMT3L promoter showed low levels of methylation in polyps and normal colonic mucosa relative to matched disease free cells with methylation level negatively correlated to expression level in normal colonic tissue. DNMT3L promoter hypomethylation was more often found in polyps harbouring KRAS mutations (p = 0.0053). BRAF mutations were common (11 out of 21 polyps), whilst KRAS mutations were identified in 4 of 21 polyps.

Conclusions

Genetic or epigenetic alterations in DNMT genes do not appear to be associated with HPS, but further investigation of genetic variation at rs62106244 is justified given the high frequency of the minor allele in this case series.     

Early-Onset Osteoarthritis,Charcot-Marie-Tooth Like Neuropathy,Autoimmune Features,Multiple Arterial Aneurysms and Dissections: An Unrecognized and Life Threatening Condition

Background

Severe osteoarthritis and thoracic aortic aneurysms have recently been associated with mutations in the SMAD3 gene, but the full clinical spectrum is incompletely defined.

Methods

All SMAD3 gene mutation carriers coming to our centre and their families were investigated prospectively with a structured panel including standardized clinical workup, blood tests, total body computed tomography, joint X-rays. Electroneuromyography was performed in selected cases.

Results

Thirty-four SMAD3 gene mutation carriers coming to our centre were identified and 16 relatives were considered affected because of aortic surgery or sudden death (total 50 subjects). Aortic disease was present in 72%, complicated with aortic dissection, surgery or sudden death in 56% at a mean age of 45 years. Aneurysm or tortuosity of the neck arteries was present in 78%, other arteries were affected in 44%, including dissection of coronary artery. Overall, 95% of mutation carriers displayed either aortic or extra-aortic arterial disease. Acrocyanosis was also present in the majority of patients. Osteoarticular manifestations were recorded in all patients. Joint involvement could be severe requiring surgery in young patients, of unusual localization such as tarsus or shoulder, or mimicking crystalline arthropathy with fibrocartilage calcifications. Sixty eight percent of patients displayed neurological symptoms, and 9 suffered peripheral neuropathy. Electroneuromyography revealed an axonal motor and sensory neuropathy in 3 different families, very evocative of type II Charcot-Marie-Tooth (CMT2) disease, although none had mutations in the known CMT2 genes. Autoimmune features including Sjogren’s disease, rheumatoid arthritis, Hashimoto’s disease, or isolated autoantibodies- were found in 36% of patients.

Interpretation

SMAD3 gene mutations are associated with aortic dilatation and osteoarthritis, but also autoimmunity and peripheral neuropathy which mimics type II Charcot-Marie-Tooth.     

Comprehensive mutation analysis in colorectal flat adenomas

Background

Flat adenomas are a subgroup of colorectal adenomas that have been associated with a distinct biology and a more aggressive clinical behavior compared to their polypoid counterparts. In the present study, we aimed to compare the mutation spectrum of 14 cancer genes, between these two phenotypes.

Methods

A consecutive series of 106 flat and 93 polypoid adenomas was analyzed retrospectively for frequently occurring mutations in “hot spot” regions of KRAS, BRAF, PIK3CA and NRAS, as well as selected mutations in CTNNB1 (β-catenin), EGFR, FBXW7 (CDC4), PTEN, STK11, MAP2K4, SMAD4, PIK3R1 and PDGFRA using a high-throughput genotyping technique. Additionally, APC was analyzed using direct sequencing.

Results

APC mutations were more frequent in polypoid adenomas compared to flat adenomas (48.5% versus 30.3%, respectively, p = 0.02). Mutations in KRAS, BRAF, NRAS, FBXW7 and CTNNB1 showed similar frequencies in both phenotypes. Between the different subtypes of flat adenomas (0-IIa, LST-F and LST-G) no differences were observed for any of the investigated genes.

Conclusion

The lower APC mutation rate in flat adenomas compared to polypoid adenomas suggests that disruption of the Wnt-pathway may occur via different mechanisms in these two phenotypes. Furthermore, in contrast to previous observations our results in this large well-defined sample set indicate that there is no significant association between the different morphological phenotypes and mutations in key genes of the RAS-RAF-MAPK pathway.     

BRCA1 and BRCA2 germline mutations in Malaysian women with early-onset breast cancer without a family history

Background

In Asia, breast cancer is characterised by an early age of onset: In Malaysia, approximately 50% of cases occur in women under the age of 50 years. A proportion of these cases may be attributable, at least in part, to genetic components, but to date, the contribution of genetic components to breast cancer in many of Malaysia''s ethnic groups has not been well-characterised.

Methodology

Given that hereditary breast carcinoma is primarily due to germline mutations in one of two breast cancer susceptibility genes, BRCA1 and BRCA2, we have characterised the spectrum of BRCA mutations in a cohort of 37 individuals with early-onset disease (≤40 years) and no reported family history. Mutational analysis of BRCA1 and BRCA2 was conducted by full sequencing of all exons and intron-exon junctions.

Conclusions

Here, we report a total of 14 BRCA1 and 17 BRCA2 sequence alterations, of which eight are novel (3 BRCA1 and 5 BRCA2). One deleterious BRCA1 mutation and 2 deleterious BRCA2 mutations, all of which are novel mutations, were identified in 3 of 37 individuals. This represents a prevalence of 2.7% and 5.4% respectively, which is consistent with other studies in other Asian ethnic groups (4–9%).     

A new case with 10q23 interstitial deletion encompassing both PTEN and BMPR1A narrows the genetic region deleted in juvenile polyposis syndrome

We report on a patient with a contiguous interstitial germline deletion of chromosome 10q23, encompassing BMPR1A and PTEN, with clinical manifestations of juvenile polyposis and minor symptoms of Cowden syndrome (CS) and Bannayan–Riley–Ruvalcaba syndrome (BRRS). The patient presented dysmorphic features as well as developmental delay at the age of 5 months. Multiple polyps along all parts of the colon were diagnosed at the age of 3 years, following an episode of a severe abdominal pain and intestinal bleeding. The high-resolution comparative genomic hybridisation revealed a 3.7-Mb deletion within the 10q23 chromosomal region: 86,329,859–90,035,024. The genotyping with four polymorphic microsatellite markers confirmed a de novo 10q deletion on the allele with a paternal origin, encompassing both PTEN and BMPR1A genes. The karyotype analysis additionally identified a balanced translocation involving chromosomes 5q and 7q, and an inversion at chromosome 2, i.e. 46,XY,t(5;7)(q13.3-q36), inv(2)(p25q34). Although many genetic defects were detected, it is most likely that the 10q23 deletion is primarily the cause for the serious phenotypic manifestations. The current clinical findings and deletion of BMPR1A indicate a diagnosis of severe juvenile polyposis, but the existing macrocephaly and PTEN deletion also point to either CS or BRRS, which cannot be ruled out at the moment because of their clinical manifestation later in life and the de novo character of the deletion. The deletion detected in our patient narrows the genetic region deleted in all reported cases with juvenile polyposis by 0.04 Mb from the telomeric side, mapping it to the region chr10:88.5–90.03Mb (GRCh37/hg19), with an overall length of 1.53 Mb.     

Systematic Study on Genetic and Epimutational Profile of a Cohort of Amsterdam Criteria-Defined Lynch Syndrome in Singapore

Background

Germline defects of mismatch repair (MMR) genes underlie Lynch Syndrome (LS). We aimed to gain comprehensive genetic and epigenetic profiles of LS families in Singapore, which will facilitate efficient molecular diagnosis of LS in Singapore and the region.

Methods

Fifty nine unrelated families were studied. Mutations in exons, splice-site junctions and promoters of five MMR genes were scanned by high resolution melting assay followed by DNA sequencing, large fragment deletions/duplications and promoter methylation in MLH1, MSH2, MSH6 and PMS2 were evaluated by multiplex ligation-dependent probe amplification. Tumor microsatellite instability (MSI) was assessed with five mononucleotide markers and immunohistochemical staining (IHC) was also performed.

Results

Pathogenic defects, all confined to MLH1 and MSH2, were identified in 17 out of 59 (28.8%) families. The mutational spectrum was highly heterogeneous and 28 novel variants were identified. One recurrent mutation in MLH1 (c.793C>T) was also observed. 92.9% sensitivity for indication of germline mutations conferred by IHC surpassed 64.3% sensitivity by MSI. Furthermore, 15.6% patients with MSS tumors harbored pathogenic mutations.

Conclusions

Among major ethnic groups in Singapore, all pathogenic germline defects were confined to MLH1 and MSH2. Caution should be applied when the Amsterdam criteria and consensus microsatellite marker panel recommended in the revised Bethesda guidelines are applied to the local context. We recommend a screening strategy for the local LS by starting with tumor IHC and the hotspot mutation testing at MLH1 c.793C>T followed by comprehensive mutation scanning in MLH1 and MSH2 prior to proceeding to other MMR genes.     

Novel insertion mutation p.Asp610GlyfsX23 in APC gene causes familial adenomatous polyposis in Chinese families

Objective

The aim of the study was to identify the causative gene defects associated with familial adenomatous polyposis (FAP) in two Chinese pedigrees.

Methods

The diagnosis of FAP patients was confirmed by clinical manifestations, family histories, colonoscopy and pathology examinations. Blood samples were collected and genomic DNA was extracted. The mutation analysis of the adenomatous polyposis coli (APC) and human mutY homolog (MUTYH) genes was conducted by direct polymerase chain reaction (PCR) sequencing and multiplex ligation-dependent probe amplification (MLPA).

Results

In pedigree A, the results of direct PCR sequencing revealed a heterozygous insertion mutation at codon 610 in exon 15 of APC gene (c.1828_1829insG), which resulted in frameshift change (p.Asp610GlyfsX23) in all 4 patients, but was absent in the unaffected familial members and controls. In pedigree B, we didn't identify that causative mutations cosegregated with the clinical phenotype in the APC and MUTYH genes.

Conclusions

We identified a novel insertion mutation as the pathogenic gene of FAP in Chinese population, which could enrich the germline mutation spectrum of APC gene, and the prophylactic proctocolectomy for the mutation carrier in family should be considered.     

Germline PIK3CA and AKT1 Mutations in Cowden and Cowden-like Syndromes

Cowden syndrome (CS) is a difficult-to-recognize multiple hamartoma syndrome with high risks of breast, thyroid, and other cancers. Germline mutations in PTEN on 10q23 were found to cause 85% of CS when accrued from tertiary academic centers, but prospective accrual from the community over the last 12 years has revealed a 25% PTEN mutation frequency. PTEN is the phosphatase that has been implicated in a heritable cancer syndrome and subsequently in multiple sporadic cancers and developmental processes. PTEN antagonizes the AKT1/PI3K signaling pathway and has roles in cell cycle, migration, cell polarity, and apoptosis. We report that 8 of 91 (8.8%) unrelated CS individuals without germline PTEN mutations carried 10 germline PIK3CA mutations (7 missense, 1 nonsense, and 2 indels) and 2 (2.2%) AKT1 mutations. These mutations result in significantly increased P-Thr308-AKT and increased cellular PIP3. Our observations suggest that PIK3CA and AKT1 are CS susceptibility genes.     

Germline BAP1 inactivation is preferentially associated with metastatic ocular melanoma and cutaneous-ocular melanoma families

Background

BAP1 has been shown to be a target of both somatic alteration in high-risk ocular melanomas (OM) and germline inactivation in a few individuals from cancer-prone families. These findings suggest that constitutional BAP1 changes may predispose individuals to metastatic OM and that familial permeation of deleterious alleles could delineate a new cancer syndrome.

Design

To characterize BAP1''s contribution to melanoma risk, we sequenced BAP1 in a set of 100 patients with OM, including 50 metastatic OM cases and 50 matched non-metastatic OM controls, and 200 individuals with cutaneous melanoma (CM) including 7 CM patients from CM-OM families and 193 CM patients from CM-non-OM kindreds.

Results

Germline BAP1 mutations were detected in 4/50 patients with metastatic OM and 0/50 cases of non-metastatic OM (8% vs. 0%, p = 0.059). Since 2/4 of the BAP1 carriers reported a family history of CM, we analyzed 200 additional hereditary CM patients and found mutations in 2/7 CM probands from CM-OM families and 1/193 probands from CM-non-OM kindreds (29% vs. 0.52%, p = .003). Germline mutations co-segregated with both CM and OM phenotypes and were associated with the presence of unique nevoid melanomas and highly atypical nevoid melanoma-like melanocytic proliferations (NEMMPs). Interestingly, 7/14 germline variants identified to date reside in C-terminus suggesting that the BRCA1 binding domain is important in cancer predisposition.

Conclusion

Germline BAP1 mutations are associated with a more aggressive OM phenotype and a recurrent phenotypic complex of cutaneous/ocular melanoma, atypical melanocytic proliferations and other internal neoplasms (ie. COMMON syndrome), which could be a useful clinical marker for constitutive BAP1 inactivation.     

SMAD3 Is Associated with the Total Burden of Radiographic Osteoarthritis: The Chingford Study

Background

A newly-described syndrome called Aneurysm-Osteoarthritis Syndrome (AOS) was recently reported. AOS presents with early onset osteoarthritis (OA) in multiple joints, together with aneurysms in major arteries, and is caused by rare mutations in SMAD3. Because of the similarity of AOS to idiopathic generalized OA (GOA), we hypothesized that SMAD3 is also associated with GOA and tested the hypothesis in a population-based cohort.

Methods

Study participants were derived from the Chingford study. Kellgren-Lawrence (KL) grades and the individual features of osteophytes and joint space narrowing (JSN) were scored from radiographs of hands, knees, hips, and lumbar spines. The total KL score, osteophyte score, and JSN score were calculated and used as indicators of the total burden of radiographic OA. Forty-one common SNPs within SMAD3 were genotyped using the Illumina HumanHap610Q array. Linear regression modelling was used to test the association between the total KL score, osteophyte score, and JSN score and each of the 41 SNPs, with adjustment for patient age and BMI. Permutation testing was used to control the false positive rate.

Results

A total of 609 individuals were included in the analysis. All were Caucasian females with a mean age of 60.9±5.8. We found that rs3825977, with a minor allele (T) frequency of 20%, in the last intron of SMAD3, was significantly associated with total KL score (β = 0.14, P_permutation = 0.002). This association was stronger for the total JSN score (β = 0.19, P_permutation = 0.002) than for total osteophyte score (β = 0.11, P_permutation = 0.02). The T allele is associated with a 1.47-fold increased odds for people with 5 or more joints to be affected by radiographic OA (P_permutation = 0.046).

Conclusion

We found that SMAD3 is significantly associated with the total burden of radiographic OA. Further studies are required to reveal the mechanism of the association.     

Somatic mutation profiles of MSI and MSS colorectal cancer identified by whole exome next generation sequencing and bioinformatics analysis

Background

Colorectal cancer (CRC) is with approximately 1 million cases the third most common cancer worldwide. Extensive research is ongoing to decipher the underlying genetic patterns with the hope to improve early cancer diagnosis and treatment. In this direction, the recent progress in next generation sequencing technologies has revolutionized the field of cancer genomics. However, one caveat of these studies remains the large amount of genetic variations identified and their interpretation.

Methodology/Principal Findings

Here we present the first work on whole exome NGS of primary colon cancers. We performed 454 whole exome pyrosequencing of tumor as well as adjacent not affected normal colonic tissue from microsatellite stable (MSS) and microsatellite instable (MSI) colon cancer patients and identified more than 50,000 small nucleotide variations for each tissue. According to predictions based on MSS and MSI pathomechanisms we identified eight times more somatic non-synonymous variations in MSI cancers than in MSS and we were able to reproduce the result in four additional CRCs. Our bioinformatics filtering approach narrowed down the rate of most significant mutations to 359 for MSI and 45 for MSS CRCs with predicted altered protein functions. In both CRCs, MSI and MSS, we found somatic mutations in the intracellular kinase domain of bone morphogenetic protein receptor 1A, BMPR1A, a gene where so far germline mutations are associated with juvenile polyposis syndrome, and show that the mutations functionally impair the protein function.

Conclusions/Significance

We conclude that with deep sequencing of tumor exomes one may be able to predict the microsatellite status of CRC and in addition identify potentially clinically relevant mutations.     

Honey bee PTEN--description, developmental knockdown, and tissue-specific expression of splice-variants correlated with alternative social phenotypes

Background

Phosphatase and TENsin (PTEN) homolog is a negative regulator that takes part in IIS (insulin/insulin-like signaling) and Egfr (epidermal growth factor receptor) activation in Drosophila melanogaster. IIS and Egfr signaling events are also involved in the developmental process of queen and worker differentiation in honey bees (Apis mellifera). Here, we characterized the bee PTEN gene homologue for the first time and begin to explore its potential function during bee development and adult life.

Results

Honey bee PTEN is alternatively spliced, resulting in three splice variants. Next, we show that the expression of PTEN can be down-regulated by RNA interference (RNAi) in the larval stage, when female caste fate is determined. Relative to controls, we observed that RNAi efficacy is dependent on the amount of PTEN dsRNA that is delivered to larvae. For larvae fed queen or worker diets containing a high amount of PTEN dsRNA, PTEN knockdown was significant at a whole-body level but lethal. A lower dosage did not result in a significant gene down-regulation. Finally, we compared same-aged adult workers with different behavior: nursing vs. foraging. We show that between nurses and foragers, PTEN isoforms were differentially expressed within brain, ovary and fat body tissues. All isoforms were expressed at higher levels in the brain and ovaries of the foragers. In fat body, isoform B was expressed at higher level in the nurse bees.

Conclusion

Our results suggest that PTEN plays a central role during growth and development in queen- and worker-destined honey bees. In adult workers, moreover, tissue-specific patterns of PTEN isoform expression are correlated with differences in complex division of labor between same-aged individuals. Therefore, we propose that knowledge on the roles of IIS and Egfr activity in developmental and behavioral control may increase through studies of how PTEN functions can impact bee social phenotypes.