Sex Determination in Vertebrates

Abstract

Vertebrate sex determination may be the most evolutionarily diverse developmental process known. While the determination of the body axis, or development of the eye or heart employs highly conserved pathways across vertebrates, the problem of how to determine sex seems to have been solved in many different ways across species. In some cases, this involves the appearance of a novel upstream regulator that gains control of the downstream pathway. However, in other cases, the downstream pathway itself seems to involve different genes, or even when the same genes are involved, they do not maintain the same order in the pathway: cassettes of genes display heterochronic expression patterns (Czerwinski, Natarajan, Barske, Looger, & Capel, 2016). What's more, in mammals a cell fate decision in the supporting cell lineage (to differentiate as pre-Sertoli or pre-granulosa cells) controls the process of sex determination and recruits other cells to follow suit (Koopman, 2016). However, in fish, germ cells seem to play the dominant role, with increases in germ cell number leading to female development, and decreases in germ cell number leading to male (Kossack & Draper, 2019; Tanaka, 2019).