Reproduction is the process by which biological entities are manufactured through biological methods. Reproduction is one of the basic phenomena common to all life. Every existing individual is the result of a previous generation's reproduction. Known reproduction methods can be divided into two broad categories: sexual reproduction and asexual reproduction. The process of asexual reproduction involves only one individual. Common asexual reproduction includes vegetative organ reproduction, budding reproduction, fragmented reproduction, (asexual) spore reproduction, and so on. Tissue culture in vitro is also a means of asexual reproduction. An ant, scientifically called Mycocepurus smithii, also breeds its offspring by asexual reproduction. The lower organisms are mostly asexual reproduction.
The male and female germ cells combine to form a fertilized egg and develop into a new individual reproductive mode. The advantage of sexual reproduction is that it can produce new mutations. Sexual reproduction involves two individuals of different sexes. For example, human reproduction is a kind of sexual reproduction. In general, higher organisms are reproduced sexually, while lower organisms are mostly reproduced asexually.
The asexual reproduction process involves only one individual, and the parent does not produce the offspring individual's reproductive mode through the combination of amphipathic cells. For example, bacteria reproduce asexually by cell division. Asexual reproduction is not limited to single-celled organisms. Most plants can reproduce asexually. Common asexual reproduction includes vegetative reproduction, budding reproduction, (asexual) spore reproduction and so on. Through in vitro plant tissue culture, animal cloning is also a means of asexual reproduction.
1. Estrogen receptor
The estrogen receptor in the uterus is mainly ERβ, which can stimulate uterine growth. The expression of GPER1 in endometrial cancer is higher than that in normal endometrium. ERα is mainly expressed in follicular vesicle membrane cells and some stromal cells. ERβ is present in granulosa cells that grow follicles and can also be expressed in some stromal cells. Studies have found that GPER1 expression in the ovaries begins with primitive follicles, but it is very low in ovarian cancer. The expression of ERβ and ERα was found in mammary epithelial cells (mammary ducts and lobules) and stromal cells, but not in lobular epithelium. ERα is important for breast development and lactation, while ERβ is not related, and its expression increases with age. The presence of GPER1 on human breast cancer cell membranes can promote the rapid activation of MAPK and Akt kinase signaling pathways. GPER1 affects the size and metastasis of breast tumors, and GPER1 has a positive relationship with tumor size.
Figure 1. Protein structure of estrogen receptor.
2. Androgen receptors
Androgen receptors are a kind of protein molecules, which are mostly present in the cells of the target organs, and can specifically bind to hormones to form hormone-receptor complexes, allowing hormones to exert their biological effects. The main form of androgens is testosterone, androgen plays an important role in the body. In addition to being related to reproduction, it also has the ability to maintain hormone balance in the body; stimulate protein anabolic metabolism, promote nitrogen deposition, and increase the number and thickness of muscle fibers. The estrogen receptor (ER) can be located at the cell membrane, cytoplasm, or nucleus. The classical nuclear receptor is located in the nucleus, and its protein is temporarily located in the cytoplasm after translation, so it can be detected in the cytoplasm. The estrogen that has spread to the nucleus binds to its nuclear receptors, triggering gene regulation mechanisms and regulating the transcription of downstream genes.
Figure 2. Protein structure of androgen receptors.
3. Sex hormone-binding globulin, SHBG
Sex hormone-binding globulin (SHBG), also known as testosterone-estradiol binding globulin, is a carrier of sex hormones. It changes during the action of sex hormones and under various physiological and pathological conditions and meaning.
Figure 3. Protein structure of sex hormone-binding globulin (SHBG).
1. Female hirsutism and virilization SHBG content in female hirsutism and virilization diseases is only 50% of the normal value, while the free T content has increased by almost 90%. Therefore, the determination of SHBG in such diseases can be used not only as a diagnostic indicator, but also as a basis for measuring the effect of treatment.
2. Polycystic ovary syndrome, obesity, hypothyroidism, and decreased SHBG levels.
3. Male hypogonadism, SHBG levels increase, and plasma T levels are often normal. During hyperthyroidism, SHBG levels rise.
4. Liver disease: liver cirrhosis, chronic hepatitis, fatty liver SHBG levels increased.
5. Serum sex hormone binding globulin increases in premature breasts. The experimental results show that the increase of SHBG in premature breasts is due to the low bioactive testosterone, which changes the estrogen/androgen ratio in breast tissue.
1. Somboonporn W.; et al. Testosterone effects on the breast: implications for testosterone therapy for women. Endocrine Reviews. 2004, 25 (3): 374-388.