Clinical significance of focal and diffuse thyroid diseases identified by (18)F-fluorodeoxyglucose positron emission tomography.

(18)F-Fluorodeoxyglucose positron emission tomography (FDG-PET) thyroid incidentalomas are defined abnormal FDG uptake in the thyroid gland found at PET scan performed as part of a staging protocol and follow-up of patients with various kinds of malignancies. In the present study we report two cases of FDG PET thyroid incidentalomas, and review the literature with regard to the meaning of this new category of thyroid "disease". Since the advent of whole body FDG PET scan, a relatively high incidence of cases of thyroid FDG uptake has been reported as an incidental finding as in one of our patient. Focal uptake was found to be more likely associated to a malignant lesion, while a diffuse thyroid uptake to a benign thyroid disease. However, differential diagnosis is difficult, and reported data in literature are somewhat discordant. A focal thyroid uptake of FDG incidentally discovered at PET scan cannot be invariably considered a malignant thyroid nodule, however a prompt and complete work-up including laboratory examinations, ultrasonography and fine needle aspiration cytology, should be obtained to exclude a thyroid carcinoma. On the other hand, patients with a PET finding of diffuse FDG uptake can be considered at low risk of malignancy, being more likely associated to chronic thyroiditis or diffuse thyroid autonomy.

Pollen tubes of Nicotiana alata express two genes from different beta-glucan synthase families.

The walls deposited by growing pollen tubes contain two types of beta-glucan, the (1,3)-beta-glucan callose and the (1,4)-beta-glucan cellulose, as well as various alpha-linked pectic polysaccharides. Pollen tubes of Nicotiana alata Link et Otto, an ornamental tobacco, were therefore used to identify genes potentially encoding catalytic subunits of the callose synthase and cellulose synthase enzymes. Reverse transcriptase-polymerase chain reactions (RT-PCR) with pollen-tube RNA and primers designed to conserved regions of bacterial and plant cellulose synthase (CesA) genes amplified a fragment that corresponded to an abundantly expressed cellulose-synthase-like gene named NaCslD1. A fragment from a true CesA gene (NaCesA1) was also amplified, but corresponding cDNAs could not be identified in a pollen-tube library, consistent with the very low level of expression of the NaCesA1 gene. RT-PCR with pollen-tube RNA and primers designed to regions conserved between the fungal FKS genes [that encode (1,3)-beta-glucan synthases] and their presumed plant homologs (the Gsl or glucan-synthase-like genes) amplified a fragment that corresponded to an abundantly expressed gene named NaGsl1. A second Gsl gene detected by RT-PCR (NaGsl2) was expressed at low levels in immature floral organs. The structure of full-length cDNAs of NaCslD1, NaCesA1, and NaGsl1 are presented. Both NaCslD1 and NaGsl1 are predominantly expressed in the male gametophyte (developing and mature pollen and growing pollen tubes), and we propose that they encode the catalytic subunits of two beta-glucan synthases involved in pollen-tube wall synthesis. Different beta-glucans deposited in one cell type may therefore be synthesized by enzymes from different gene families.