logo

Bangladesh Agricultural University (BAU)

Publish Date: 12 Oct 2021

Research activities

Author:

Share this on

I carried out doctoral research on the in vitro growth culture of bovine growing oocytes in Reproductive Biotechnology Laboratory in Kobe University, Japan. Bovine oocytes increase in diameter from 30 µm to 125 µm, and acquire the competence to mature to metaphase II (MII). At the same time, granulosa cells surrounding the oocytes proliferate, and an antrum is formed inside the follicles. Bovine growing oocytes with the diameter of >100 µm are able to resume meiosis, although they are incompetent to mature to MII. Thus, these oocytes are considered “partially meiotic-competent”, and their precocious resumption of meiosis during growth culture makes it difficult for them to grow to fully meiotic-competent oocytes. I examined the effect of phosphodiesterase (PDE) inhibitors, which prevent degradation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), on the growth of partially meiotic-competent oocytes and obtained the following results.
i) PDE3 inhibitors induced formation of antrum-like structures in bovine oocyte-granulosa cell complexes (OGCs) and maintained meiotic arrest of the oocytes during culture, whereas PDE4 inhibitors were ineffective on both phenomena. PDE3 inhibitors also maintained gap junctional communication between oocytes and granulosa cells. In the subsequent in vitro maturation, bovine oocytes fully-grown with PDE3 inhibitors matured to metaphase II.
ii) Since formation of the antrum-like structures in bovine OGCs was promoted with the inhibition of PDE3, which is functional only in oocytes, I thought that the PDE3 inhibitors might promote production of some oocyte-derived factors, which in turn induce the formation of antrum-like structures in OGCs. I examined effects of oocyte-derived growth factors “growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15)” on the formation of antrum-like structures in bovine OGCs and consequently obtained the following results. By the culture without the oocyte-derived growth factors, bovine OGCs formed antrum-like structures, whereas oocytectomized complexes (OXCs which were prepared by the removal of oocytes from OGCs) and granulosa cell complexes (GCs which were composed only of granulosa cells) did not develop the structure. However, treatment with recombinant GDF9 and BMP15 induced formation of antrum-like structures in OXCs and GCs (without oocytes which were suppliers of these growth factors). In addition, I also observed that granulosa cells in culture dishes which migrate away from the oocyte-granulosa cell complexes changed their morphology as fibroblast-like, rhomboid-like and pebble-like cell structures in the absence of GDF9 and BMP15. From that result I assumed that GDF9 and BMP15 regulate morphology of granulosa cells.
iii) I examined effects of PDE inhibitors on the expression of GDF9 and BMP15 mRNAs in in vitro grown bovine oocytes. The relative expression levels of GDF9 and BMP15 mRNAs increased in the oocytes after culture with PDE3 inhibitors, whereas the PDE4 inhibitors rarely enhanced the mRNA expression of these oocyte-derived factors.
iv) Based on these results, I concluded that PDE3s of bovine OGCs promotes precocious maturation of bovine oocytes before full growth, and that bovine oocytes synthesize GDF9 and BMP15 in response to reduction of the PDE3 activity and these growth factors induce formation of antrum-like structures by the granulosa cells. The findings of my studies can contribute to the development of the treatments for infertility and subfertility which are due to the abnormalities in the processes of follicular development, gonadotropin surge, sperm transportation and implantation of both animals and humans.
In Bangladesh, the breeding of domestic animals has a serious problem of low reproductive performances in both males and females. In order to overcome this problem, I also have been carrying out research on reproduction of native Black Bengal goats, sheep, buffaloes, bovine and crossbred rabbits at Animal Science Laboratory of Bangladesh Agricultural University. My studies with the hormone, growth factor and amino acid showed promising effects on animal reproduction and were useful to produce more offspring’s in a given time. Moreover, it is also possible to store female reproductive germ cells from superior quality breed using cryopreservation techniques for future use. On the other hand, kid mortality due to lack of milk is a major cause of economic loss for animal husbandry in Bangladesh. Feeding milk replacer reduce kid mortality, promote rumen development and increase the chance of economic profit for the farmers. The findings from my study also proposed the best way of animal rearing to get maximum reproductive performance. In addition, I suggest an easy and useful method of pregnancy detection of domestic animals, and the best timing of animal re-matting for better growth of newborn which are crucial for management of a farm and achievement of profit.

Others Post