Introduction

In a relatively condensed manner, this chapter attempts to portray some of the highlights during formation of the eutherian gonads. These organs are uniquely derived from migration and movement of germinal and somatic cells, and give the first clear evidence of sexual dimorphism in specific tissues. The treatment that follows focuses on the question of their origins during early embryogenesis and then on the nature of the interactions as the cell lines of the gonad differentiate and develop. Although discussion at the level of cellular organisation is both stimulating and illuminating as a teaching approach, and in the present instance emphasises the proximity between embryonic renal, gonadal and adrenal tissues, the ultimate and incisive problem for the 1990s must concern the regulation of gonadal formation at the molecular level. Precisely how does gene action programme cellular differentiation to establish the respective lineages? At the time of writing, an appropriate body of information is not available on this topic, although it is assumed that specific proteins are induced to regulate transcription.

Numerous reviews exist on the processes involved in formation of the gonads in eutherian mammals. Extensive treatments include those of Gillman (1948), Witschi (1951), Burns (1961), Clermont & Huckins (1961), Clark & Eddy (1975), Zuckerman & Weir (1977), Jones (1978), McLaren (1981 a), Baker (1982), Byskov (1981, 1982, 1986), Byskov & Høyer (1988), Wartenberg (1989) and Jost & Magre (1993).