Submitted
by: Sonika Kar (Reg. No.17LAPH06)

Department of Animal Biology, School of Life
Sciences, University of Hyderabad,

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Gachibowli, P O Central University, Hyderabad
500 046, Telangana, India.

Supervisor: Prof. B. Senthilkumaran

Abstract

Steroidogenesis
is a process which governs the conversion of cholesterol to active steroid
hormones. The de novo biosynthesis of
active steroid hormones from the precursor, cholesterol, involves the
mobilization of cholesterol from the cellular stores to the inner mitochondrial
membrane in order to produce the first steroid hormone, pregnenolone. This
trafficking of cholesterol to the inner mitochondrial membrane is accomplished
by the actions of steroidogenic
acute regulatory protein (StAR) and thereby initiating the conversion of
cholesterol into several steroid hormones via a series of enzymatic steps. This
review article summarizes the current knowledge of the enzymatic regulation of
steroidogenesis with special reference to males. Most of the steroidogenic
enzymes are either cytochrome P450(s) or hydroxysteroid dehydrogenase(s). The
cytochrome P450 enzymes are unidirectional and the cleavage reactions
facilitated by these enzymes are irreversible due to which the accumulation of
the products does not drive flux backto the precursor unlike the reactions
mediated by the hydroxysteroid dehydrogenase(s) that are mostly reversible. Significant
advances have arisen over past three decades in the understanding of the molecular
characterization of these steroidogenic enzymes that have prompted several
scientists to look upon the aspects of steroidogenic regulation in detail. Some
of the recent findings include identification, molecular cloning and
characterization of different steroidogenic enzymes genes and associated
transcription factors in lower vertebrates. This review attempts to impart an
integrative view on the regulation of testicular development and
spermatogenesis together with the characteristics of few candidate
proteins/factors that are involved in the processes with an emphasis on teleost
fish. Highlights on the crosstalk of factors governing these two processes will
be discussed in terms of sex-reversal and artificial induction to provide an
outlook to understand male reproduction in teleosts.

Keywords:                                                                                                                                   

Steroidogenesis;
steroid
hormones; sex reversal;
spermatogenesis; steroidogenic enzyme genes.