The Study On Cell Proliferation And Apoptosis During Oogenesis Of Reticulitermes Aculabialis

The evolution of eusociality in all existing termites remains one of the great mysteries in biology. They are the most ancient eusocial insects, and complex and wonderful structures emerging from the cooperation and differentiation of a large number of individuals. Because of their special and wonderful of the biological characteristics and harming to human beings, researchers all over the world pay attention to the termites.Reticuliiermes aculabialis (Isoptera:Rhinotermitidae) belongs to harmful insect, which damages mainly public buildings. At present, the development of the gonads and germ cells, cell proliferation and apoptosis during oogenesis were investigated by microscopic histology, BrdU immunohistochemistry and TUNEL methods for exploring the special caste differentiation and reproductive mechanism in Reiiculitermes aculabialis. The main results describe as follows:1. Solider caste is a definitive and terminal stage of development, so they are completely sterile and no longer have the ability of transforming other castes. In the present study, the size of the ovaries and the process of the oogenesis in the soldiers and workers were investigated by HE (haematoxylin-eosin) staining. The results indicated that the sectional area of ovary in the worker caste was7times that of the soldier caste and the gonad size was significantly different in these two castes (P<0.01). Compared with workers, oogenesis of the soldier caste only had differentiation stage of germ cells and didn’t reach the growth stage. Furthermore, germ cells of the soldier caste were significantly smaller than those of workers at the differentiation stage; the volume ratio (soldier:worker) was1:16. The results prove that further degradation of the ovary occurs as workers become soldiers causing soldiers to lose their potential reproductive ability. Our results provide histological evidence for soldier infertility, and also show that there is a histological basis for the difference in potential reproductive capacity between soldiers and workers.2. The very swollen abdomen and powerful fecundity of the queen is related directly to the highly-developed ovaries. Through the comparison between the ovarian development and the oogenesis in the queen and alate reproductives of Reticulitermes aculabialis, this paper showed that ovary of the queen almost took the whole abdominal cavity from the first somite to the last, and the end of the abdominal cavity was wholly filled with ovarioles, while ovaries of the alate reproductives only distributed in narrow area of pleon; The size of ovary was significantly different between the queen and the alate reproductives (P<0.01) and the ratio of length of ovarian between them was3.5:1and the width was3:1, and the ovarian size of the queen was19times that of the alate reproductives. There was a significant difference on the number of oocytes in every phase during oogenesis between the queen and the alate reproductives (P<0.01). The number of germ cells of the queen was about130±9at the differentiation stage.99±6at the growth stage and27±3at the stage of deposition yolk. Compared with the queen, the number of germ cells in alate reproductives was little, and only was about3±1at the yolk accumulation phase. These results suggest that size of ovary, the number of germ cells and reproductive capacity tend to increase with the process from a new group to a mature colony. The powerful reproductive ability of the queen has a direct relationship with the size of the ovary and a large number of germ cells. Our results provide histological evidence for the further study that reproductive ability and regulation mechanism of ovarian development during the development of the queen.3. Germ cells and follicle cells showed cell proliferation during oogenesis of reproductives and this phenomenon displayed the pattern of stage-specific. Cell proliferation plays a vital role and profound significance in maintaining the relative balance of the cell number and the normal development of oocytes during oogenesis. In the present study, germ cells displayed the BrdU positiving at the differentiation stage of germ cells during the normal oogenesis of Reticulitermes aculabialis. And at the oocyte growth and the early stage of yolk deposition, follicle cells showed the phenomenon of the BrdU positiving. The differentiation stage of oocytes is the earliest stage during oogenesis, and cell proliferation during this stage not only ensures the quantity of mature ovum and supplies the aging or apoptotic cells, but also plays a vital role in the differentiation and proliferation of follicle cells; And the proliferation of follicle cells plays a vital role in enveloping and providing the nutrients and information for oocytes. During the development of oocytes and follicle cells, the balance between the proliferation and apoptosis in Reticulitermes aculabialis determines the fate of the ovarian oocytes maturation. However, for the social insects, in addition to maintaining the reproductive rate, it also has an important relationship with caste differentiation. 4. TUNEL assay showed that apoptosis occured and there was a significantly different during oogenesis of the reproductive, worker and soldier in Reticulitermes aculabialis. At the differentiation stage of the normal oogenesis in the reproductive, apoptotic cells contained germ cells and some epithelial cells. During the oocyte growth period, there had been apoptosis with a small amount of oocytes and surrounding follicular cells. At the beginning of yolk deposition stage, there had been apoptosis of follicular cells, but no oocytes of apoptosis. The highest rate of apoptosis of germ cells in the earlier developmental stage (differentiation stage) suggested that critical apoptotic checkpiont probably existed. Compared with reproductives, workers and soldiers of non-reproductive caste during oogenesis showed different regulations of the apoptosis. Our results showed that apoptosis of workers took place at the differentiation stage, and the rates of apoptosis at this stage were significantly higher than the same period of reproductives; the germ cells of soldiers only developed into the differentiation stage, so apoptosis occurred at this stage and the rate of apoptosis was significantly higher than the same period of other castes. This study indicate that the different degree apoptosis of germ cells is the direct reason for the different development level of the ovary, and reveal deeply and systematically the special reproductive mechanism of the termite.In conclusion, in comparison with the workers, the development of the gonad in the soliders were degenerated extremely. The oogenesis of soldier only had differentiation stage of germ cells and didn’t reach the other stages. It provides a fact that the soldier is completely sterile. Through the comparison between the ovarian development, the oogenesis and the number of germ cells in the queen and alate reproductives of Reticulitermes aculabialis, results suggested that the powerful spawn ability of the queen has a direct relationship with the size of ovary and a large number of germ cells. At the same time, studied cell proliferation and apoptosis during oogenesis of Reticulitermes aculabialis proved that the degree of the developmental germ cells existed. This also set a theoretical foundation on the study of caste differentiation and special reproductive mechanism.