Submitted mostly reversible. Significant advances have arisen over past

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 pregnenolone. The 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.