The ages of many mammals are estimated by counting growth layers in tooth sections, yet validation of age estimation techniques using free-ranging mammals has been problematic. Contrary to age estimates for most other animals in which it is assumed that one bipartite growth increment forms annually, beluga whale ( Delphinapterus leucas (Pallas, 1776)) age estimates have been calculated assuming that two growth layer groups (GLGs) form each year. Here we report the age validation for belugas based on date-specific incorporation of atomic bomb radiocarbon into tooth GLGs. Radiocarbon assays of dentinal layers formed in belugas harvested between 1895 and 2001 indicated that radiocarbon from atmospheric testing of nuclear weapons was incorporated into growing teeth and retained for the remaining life of the animal. Comparison of age determined by bomb radiocarbon with age determined by GLG counts indicated that GLGs form annually, not semiannually, and provide an accurate indicator of age for belugas up to at least 60 years old. Radiocarbon signatures of belugas were temporally and metabolically stable and were apparently derived more from the radiocarbon content of their prey than from water. Our understanding of many facets of beluga population dynamics is altered by the finding that this species lives twice as long as previously thought.

We compared counts of growth layer groups (GLGs) in the dentine of un‐decalcified, unstained cross‐sections and in the cementum of decalcified, stained longitudinal sections of canine teeth from 144 ringed seals (Phoca hispida). Although there was a statistically significant correlation until approximately 10 GLGs, about 75% of paired readings at ≤ 10 cementum GLGs disagreed. After 10 GLGs, the number of GLGs in the cementum usually was greater. The maximum GLG count in cementum was 33, compared to a maximum in dentine of only 19. Interobserver differences in median counts were not statistically significant using cementum or dentine counts. Regression analysis revealed that for cementum in female seals, readers differed at higher counts (P < 0.05), and for dentine, there was a constant difference of about 0.6 GLGs (P < 0.05) for male seals and 1.1 GLGs (P < 0.05) for female seals. Counting GLGs in the cementum of decalcified and stained longitudinal sections provided higher counts and more agreement between readers, and it was the better of the methods examined for ageing ringed seals.

The nucleotide and deduced amino acid sequences of the coding regions of human and rat keratinocyte transglutaminases (protein-glutamine: amine y-glutamyltransferase; EC 2.3.2.13) have been determined. These yield proteins of -90 kDa that are 92% identical, indicative of the conservation of important structural features. Alignments of amino acid sequences show substantial similarity among the keratinocyte transglutaminase, human clotting factor XIII catalytic subunit, guinea pig liver tissue transglutaminase, and the human erythrocyte band-4.2 protein. The keratinocyte enzyme is most similar to factor XIII, whereas the band-4.2 protein is most similar to the tissue transglutaminase. A salient feature of the keratinocyte transglutaminase is its 105-residue extension beyond the N terminus of the tissue transglutaminase. This extension and the unrelated activation peptide of factor XIII (a 37-residue extension) appear to be added for specialized functions after divergence of the tissue transglutaminase from their common lineage.During terminal differentiation, keratinocytes of the epidermis and other stratified squamous epithelia synthesize an envelope consisting of cross-linked protein beneath the plasma membrane (1). Localization of the envelope appears due to the presence of a membrane-bound transglutaminase (2, 3) and several of its substrate proteins at the cell periphery (4). The enzyme is anchored in the membrane by acylated fatty acid (5) and is activated by flux of Ca2+ into the cytoplasm when cellular membranes lose their integrity during the final maturation stage (6). The biochemical events resulting in mature envelopes have been difficult to follow due to the intractable nature of the highly cross-linked product. In view of the many proteins and amines in keratinocytes serving as transglutaminase substrates (4, 7), further study of the enzyme structure may help in analysis of this process. In addition to acylation, for example, phosphorylation of the membrane anchorage region has been seen, which could alter the interaction of the enzyme with potential substrate proteins (8).The blood clotting factor XIII catalytic subunit (9-11) and tissue transglutaminase (12) have recently been cloned and sequenced. These enzymes are distantly related to each other but display significant similarity in certain regions, especially around the active site. An origin of the latter region in common with thiol proteases has been proposed (9). The more recent demonstration of striking similarity between the active site and a corresponding region in the erythrocyte band-4.2 protein (13, 14), however, indicates that closer relatives of transglutaminases exist. A cDNA clone for the keratinocyte-specific enzyme of the rabbit was originally identified by using an oligonucleotide probe directed toward the active site and was partially sequenced (15). Using that clone as probe, we have now cloned and determined the complete primary structure of this third type of transglutaminase for the human and rat.O Although many type...