Mutation ofcyp19a1bresults in sterile males due to efferent duct obstruction in Nile tilapia

Abstract

The involvement of estrogen in male fertility has been well established in mammals. However, less is known about the role of estrogen in fish male reproduction. Our recent study revealed that Cyp19a1a deficiency had no effect on fertility in male fish. In this study, expression of Cyp19a1b, but not Cyp19a1a, was detected by immunohistochemistry in Leydig cells of tilapia testes. cyp19a1b mutation resulted in a significant decrease in the concentration of 17β‐estradiol in serum and sterility in XY fish, as no offspring were obtained when crossed with control XX fish at 240 days after hatching (dah). No sperm was obtained from the mature mutants by in vitro extrusion. Further examination of the mutant gonads revealed excessive semen accumulation and testicular hypertrophy. Semen collected from the mutant testes during autopsy contained sperm with a normal morphology that showed no significant differences in motility, VCL, BCF, STR, or fertility compared with control sperm. Efferent ducts from the mutant testes, which had low‐convolution levels, fewer branches, and no blood vessels observed inside the walls, were significantly smaller in size. qRT‐PCR analyses showed downregulated expression of ion exchange genes. There was increased apoptosis in the epithelial cells of the efferent ducts and other somatic cells of the testes as revealed by TUNEL staining, as well as upregulation of apoptosis gene expression in the mutants. At 360 dah, mutant fish showed testicular atrophy and efferent duct fibrosis. These results demonstrated that estrogen deficiency caused by Cyp19a1b mutation resulted in male sterility due to efferent duct obstruction.

Transcription of the Sox30 Gene Is Positively Regulated by Dmrt1 in Nile Tilapia

“…As is well known, the efferent duct is responsible for the absorption of fluid from the lumen, spermatozoon maturation, spermiophagy, and secretion of steroid hormone [31,32,33]. Recent studies reported that the male sterility caused by the mutation of either Nile tilapia Cyp19a1b or mouse Gemc1 is primarily due to the defect of efferent duct development [34,35]. Thus, further work will be needed to clarify the roles of both Sox30 and Dmrt1 in the efferent duct of the Nile tilapia testis.…”

Neuroestrogens facilitate male-typical behaviors by potentiating androgen receptor signaling in medaka

“…In tilapia ( Oreochromis niloticus ), depletion of cyp19a1b has been reported to cause male infertility due to efferent duct obstruction (17). If this is also the case in medaka, the observed behavioral defects might be secondary to infertility.…”

Dmrt1 is the only male pathway gene tested indispensable for sex determination and functional testis development in tilapia

“…The XX and XY heterozygotes for amhy , dmrt1 , gsdf , cyp19a1a , cyp19a1b and foxl3 alleles were previously generated by CRISPR/Cas9 [ 9 , 12 – 14 , 42 , 43 ]. These mutant lines were maintained in our laboratory.…”

“…The gsdf -/- ; cyp19a1a -/- ; cyp19a1b -/- triple mutants cannot be obtained by crossing using gsdf + /- ; cyp19a1a + /- double heterozygotes and cyp19a1b + /- heterozygotes. In our previous study, the cyp19a1b was efficiently targeted by CRISPR/Cas9 [ 42 ]. For generation of gsdf -/- ; cyp19a1a -/- ; cyp19a1b -/- triple mutants, the gRNA for cyp19a1b was in vitro transcription with T7 RNA polymerase followed by purification with QIAquick PCR Purification Kit (QIAGEN, Germany).…”

“…Additionally, teleost fish possess two aromatase genes, cyp19a1a (encoding ovarian aromatase) and cyp19a1b (encoding brain aromatase) [ 41 ]. There is no doubt that brain aromatase can catalyze the conversion of testosterone to estrogen [ 42 ]. In zebrafish, the follicles of dmrt1 ; cyp19a1a double mutants could develop into previtellogenic stage [ 39 , 40 ], which cannot rule out the role of Cyp19a1b that can produce E2.…”