Abstract
The insulin-like family of growth factors (IGFs) – composed of insulin, and insulin-like growth factors I (IGF1) and II (IGF2) – provides essential signals for the control of testis development and function. In the testis, IGFs act in an autocrine-paracrine manner but the extent of their actions has been underestimated due to redundancies at both the ligand and receptor levels, and the perinatal lethality of constitutive knockout mice. This review synthesizes the current understanding of how the IGF system regulates biological processes such as primary sex determination, testis development, spermatogenesis and steroidogenesis, and highlights the questions that remain to be explored.
Highlights
Male fertility depends on proper testis function
Reproductive capability is regulated by the hypothalamicpituitary-gonadal axis [5], the activity of local gonadal factors, such as those of the insulin/Insulin-like growth factor (IGF) family, modulate reproductive performance
We describe the essential roles of IGFs during sex determination and testicular development, and how they modulate the function of Sertoli cells (SCs), germ cells (GCs), and Leydig cells (LCs)
Summary
Male fertility depends on proper testis function. The testis is specified in the fetus from a bipotential gonad and its development follows an intricate course of genetic, hormonal, and growth factor expression. These results from both granulosa cells and SCs suggest a crucial role for IGFs in mediating FSH action in the gonads These data reinforce the view that the local production of insulin/IGFs is the major intratesticular signal regulating SC number, testis size and sperm output in mammals. IGF1 has been shown to stimulate the proliferation of progenitor LCs [97] Overall, these data indicate that the IGF system plays an important role in mediating the proliferation of precursor LCs and the establishment of a normal number of ALCs, and in the steroidogenic capacity of ALCs. Conclusions, perspectives and unanswered questions Recent studies have unequivocally demonstrated the essential role of the insulin family of growth factors in sex determination and reproductive function.
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