Neuroendocrine facets of human puberty

Loss of Growth Hormone Gene (gh1) in Zebrafish Arrests Folliculogenesis in Females and Delays Spermatogenesis in Males

As a master hormone controlling growth and metabolism, GH is also known to regulate reproduction. Studies in mammals have shown that mutations in GH or its receptor (GHR) not only result in retardation in body growth but also reproductive dysfunctions in both sexes. However, the roles of GH in reproduction of other vertebrates are poorly defined. In this study, we created two zebrafish GH (gh1) mutant lines using CRISPR/Cas9. The mutant developed normally up to 14 days postfertilization (dpf); however, a high rate of mortality was observed afterward in both lines, and only a small number of mutant fish could survive to adult stage. The body growth of the mutants was significantly retarded in both sexes in a gene dose-dependent manner compared with their wild-type siblings. A severe dysfunction of gonadal development was observed in survived mutant females, with ovarian folliculogenesis being arrested completely at primary growth stage until 100 dpf. Interestingly, the folliculogenesis in the mutant resumed after months of delay with a certain number of follicles entering vitellogenic growth. As for male reproduction, although the spermatogenesis in mutant males seemed normal in adults, the GH-insufficient heterozygote showed an obvious delay of spermatogenesis (puberty onset) at early developmental stages. The adult mutant males could not breed with wild-type females through natural spawning; however, the sperm isolated from the mutant testes could fertilize eggs through artificial fertilization. This study provides further genetic evidence for the dependence of puberty onset on somatic growth, but not age, in fish.

Growth hormone and reproduction: a review of endocrine and autocrine/paracrine interactions

The somatotropic axis, consisting of growth hormone (GH), hepatic insulin-like growth factor I (IGF-I), and assorted releasing factors, regulates growth and body composition. Axiomatically, since optimal body composition enhances reproductive function, general somatic actions of GH modulate reproductive function. A growing body of evidence supports the hypothesis that GH also modulates reproduction directly, exerting both gonadotropin-dependent and gonadotropin-independent actions in both males and females. Moreover, recent studies indicate GH produced within reproductive tissues differs from pituitary GH in terms of secretion and action. Accordingly, GH is increasingly used as a fertility adjunct in males and females, both humans and nonhumans. This review reconsiders reproductive actions of GH in vertebrates in respect to these new conceptual developments.

Breast cancer, stem cells and sex hormones. Part 2: the impact of the reproductive years and pregnancy

The primitive breast develops in utero and during infancy breast growth largely parallels the growth of the child. At puberty, the GnRH pulse generator starts up, initially with just 1-2 pulses daily. This results in very small amounts of unopposed estrogen being secreted by the ovary. As the GnRH pulse generator matures, ovarian secretion of estrogen increases. The pubertal breast responds to this increasing estrogen drive. Breast glandular increase in size is mostly due to growth and division of the primary ducts. Eventually, the terminal buds give rise alveolar buds which tend to cluster around a terminal duct. Lobule formation begins in the first 2 years that follow menarche. With the onset of ovulation, breast mitotic activity increases and is usually maximal in the luteal phase. The final stage of breast maturation occurs during the first full-term pregnancy. The breast undergoes marked changes in preparation for breast feeding. There is evidence that breast SC number decreases during that first pregnancy. Also, the remaining SC undergo significant change which seems to render them less likely to undergo malignant change. These alterations to breast SC number and function may explain, at least in part, why early first pregnancy reduces the risk of breast cancer later in life.

The genetic basis for sex differences in human behaviour: role of the sex chromosomes

The nature of the mechanisms underlying observed sex differences in human behaviour continues to be debated. This review concentrates on the thesis that genes on the sex chromosomes other than those directly controlling sex determination, and whose functions are, at least in part, independent from hormonal influences, play a significant role in determining gender differences in behaviour. To provide an adequate basis for examining this issue, the current understanding of the nature of sex determination, differences in behaviour and the influences of sex hormones are evaluated. The possible contribution to behavioural differences of those X-linked genes which escape inactivation, or which may be subjected to imprinting, is discussed. The review concludes with a summary of the genetic basis for two sexually disparate types of behaviour.