he loss of balance response and increased incidence of falls is of concern to physical therapists. Improvement of balance may he a desired functional outcome for many patients . Balance function has been reported to decline with age, as evidenced by increased postural sway and decreased stability (1,2,10,33,39-42,47,48). It has been estimated that one-third of the elderly living at home and twothirds of the institutionalized, aged 65 and older, will experience one or more falls per year (7,45). Many studies have found an association between falls and body sway (6,25,36); others have found no correlation between the two (2,12,39).Balance is controlled by sensory input, central processing, and neuromuscular responses. (5,15), muscular atrophy, reduction in the size and number of mitochondria, and a loss of both number and size of muscle fibers when compared with younger subjects (38). In addition, peripheral nerve conduction velocity slows, with a decrease in the rate and magnitude of reflex responses (38).Osteoarthritis is the most prevalent chronic disease affecting the over-65 population. Survey studies have found that in the 65-74 age group, 46% report having osteoarthritis (24). The incidence in the 75-79 age group is estimated between 51 % (2) and 85% (28). Knee osteoarthritis impacts the body in many ways, including reduced knee strength ( 14,18,23,34) and proprioception (3,4,43). As previously stated, both strength and proprioception are components of balance function. Age has been shown to have a detrimental effect on all determinants of balance, but the deterioration may be accelerated in the areas of proprioception and strength in those with osteoarthritis. Thus, osteoarthritis may further impair balance. Kegelmeyer (20) failed to establish such a relationship, but a small sample size and the use of a clinical assessment may not have allowed enough discrimination between groups. No other studies have objectively docu-JOSPT

We have obtained sequence data for beta-tubulin genes from eight species of Foraminifera (forams) and alpha-tubulin sequences from four species, sampling major taxonomic groups from a wide range of environments. Analysis of the beta-tubulin sequences demonstrates that foram beta-tubulins possess the highest degree of divergence of any tubulin gene sequenced to date and represent a novel form of the protein. In contrast, foram alpha-tubulin genes resemble the conventional alpha-tubulins seen in other organisms. Partition homogeneity analysis shows that the foraminiferal beta-tubulin gene has followed an evolutionary path that is distinct from that of all other organisms. Our findings indicate that positive selective pressure occurred on the beta-tubulin subunit in ancestral forams prior to their diversification. The specific substitutions observed have implications for microtubule (MT) assembly dynamics. The regions most strongly affected are implicated in lateral contacts between protofilaments and in taxol binding. We predict that these changes strengthen lateral contacts between adjacent dimers in a manner similar to that induced by taxol binding, thus allowing the formation of the tubulin "helical filaments" observed in forams by electron microscopy. Our results also indicate that substantial changes to these portions of the beta-tubulin molecule can be made without sacrificing essential MT functions.

Foraminiferal taxonomy is traditionally based on morphological characteristics, particularly the structure and composition of the test (shell). Recently, a comprehensive SSU‐based molecular phylogeny confirmed some multi‐chambered foraminiferal groups while enhancing our understanding of the single‐chambered, or the so‐called “allogromiid”, taxa. However, some relationships, such as the origin of the foraminiferal order Miliolida, remain unresolved, suggesting an approach involving multiple data sources may improve understanding. Here, we discuss the evolutionary implications of β‐tubulin genes from several species of foraminifera. Foraminiferal β‐tubulin is highly divergent, possibly indicating a period of accelerated evolution of this gene at the base of the foraminiferal lineage, but it is well‐conserved within the group. We show its utility in helping to resolve the phylogenetic position of Miliammina fusca, a foraminiferan whose proper classification has been debated for 70 years. M. fusca is a morphological “chimera”, and we show that its placement in SSU trees is not particularly robust. However, β‐tubulin data assigns Miliammina to the Miliolida, some of whose members show a similar chamber coiling pattern. This placement agrees with an earlier observation that M. fusca's actin isoforms more closely resemble those of traditional milolids. This finding implies that test formation can revert from calcareous to agglutinated, suggesting a reexamination of some relationships inferred from the fossil record. Supported by NSF OPP0003639.

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Foraminifera utilize an unusual and very rapid microtubule assembly/disassembly system: a state transition between microtubules and helical filaments. The helical filament is an assembly polymorph that forms when the microtubule lattice uncoils into a ribbon of tubulin dimers connected only by lateral subunit/subunit bonds. An unusual β‐tubulin sequence, which may be implicated in this process, has previously been reported from the foraminiferan Reticulomyxa filosa. In order to determine the taxonomic distribution and possible significance of this tubulin isoform, we sequenced and analyzed β‐tubulin genes from a broad taxonomic range of foraminifera. These genes contain a large number of substitutions, conserved within the group, which may alter the biochemical properties of β‐tubulin, especially in regions involved in subunit/subunit binding between α‐ and β‐tubulin in the microtubule lattice. In particular, the M‐loop, which is intimately involved in lateral subunit binding, shows only 30% homology to the consensus sequence for eukaryotic β‐tubulins. Multiple regions identified to be involved in longitudinal contacts with α‐tubulin are also highly substituted. In contrast, the foraminiferal α‐tubulin is well conserved with its homologs in other organisms. We suggest that these alterations to the consensus eukaryotic β‐tubulin sequence may help to explain the unusual assembly properties of foraminiferal microtubules. This work was supported by NSF OPP0003639.