The homolog of Ciboulot in the termite (Hodotermopsis sjostedti): a multimeric β-thymosin involved in soldier-specific morphogenesis

BACKGROUND: Caste differentiation in social insects is a type of polyphenism that enables division of labor among members of a colony. This elaborate social integration has attracted broad interest, although little is known about its regulatory mechanisms, especially in Isoptera (termites). In this study, we analyzed soldier differentiation in the damp-wood termite Hodotermopsis sjostedti, focusing on a possible effector gene for caste development. The gene for an actin-binding protein, HsjCib, which shows a high level of expression in developing mandibles during soldier differentiation, is characterized in detail. RESULTS: To examine the HsjCib gene, full-length cDNAs were obtained by rapid amplification of cDNA ends-polymerase chain reaction (RACE-PCR) and sequencing. Multiple isoforms were identified, and on the basis of the results of northern and Southern hybridization analyses, these isoforms were considered to be transcriptional variants from a single gene. On the basis of their sequence similarity to homologous genes of other organisms, functions in actin assembly were assumed to be different among isoforms. Expression analysis revealed high expression in the head during soldier differentiation, which was consistent with their allometric growth. Although isoform expression was observed in various tissues, different expression levels were observed among tissues, suggesting the possibility of tissue-specific morphogenetic regulation by HsjCib isoforms. CONCLUSION: This study revealed the characteristics and dynamics of the HsjCib gene during soldier differentiation as a potential representative of downstream effector genes in caste-specific morphogenesis. From the expression patterns observed, this gene is considered to be involved in cephalic morphogenesis and neural reorganization, resulting in the establishment of caste-specific morphology and behavior.