Depletion of <i>stearoyl-CoA desaturase</i> (<i>scd</i>) leads to fatty liver disease and defective mating behavior in zebrafish

Abstract

Stearyl coenzyme A desaturase (SCD), also known as delta-9 desaturase, catalyzes the rate-limiting step in the formation of monounsaturated fatty acids. In mammals, depletion or inhibition of SCD activity generally leads to a decrease in triglycerides and cholesteryl esters. However, the endogenous role of scd in teleost fish remains unknown. Here, we generated a zebrafish scd mutant ( scd -/- ) to elucidate the role of scd in lipid metabolism and sexual development. Gas chromatography-mass spectrometry (GC-MS) showed that the scd -/- mutants had increased levels of saturated fatty acids C16:0 and C18:0, and decreased levels of monounsaturated fatty acids C16:1 and C18:1. The mutant fish displayed a short stature and an enlarged abdomen during development. Unlike Scd -/- mammals, the scd -/- zebrafish showed significantly increased fat accumulation in the whole body, especially in the liver, leading to hepatic mitochondrial dysfunction and severe cell apoptosis. Mechanistically, srebf1 , a gene encoding a transcriptional activator related to adipogenesis, acc1 and acaca , genes involved in fatty acid synthesis, and dgat2 , a key gene involved in triglyceride synthesis, were significantly upregulated in mutant livers to activate fatty acid biosynthesis and adipogenesis. The scd -/- males exhibited defective natural mating behavior due to defective genital papillae but possessed functional mature sperm. All defects in the scd -/- mutants could be rescued by ubiquitous transgenic overexpression of scd . In conclusion, our study demonstrates that scd is indispensable for maintaining lipid homeostasis and development of secondary sexual characteristics in zebrafish.

Zebrafish facilitate non‐alcoholic fatty liver disease research: Tools, models and applications

“…scd knockout zebrafish showed significantly increased fat accumulation in the liver, leading to hepatic mitochondrial dysfunction and severe cell apoptosis with a typical fatty liver disease phenotype. 38 Omega-3 desaturase (Fat-1) of Caenorhabditis elegans is able to convert n-6 polyunsaturated fatty acids (PUFAs) to n-3 PUFAs. Fat-1 transgenic zebrafish Tg(CMV:fat1,CMV:EGFP) ihb22 induced a low n-6/n-3 PUFA ratio, thus alleviating lipid deposition and avoiding fatty liver induced by highvegetable oil feeding.…”

“…Stearyl‐CoA desaturase catalyses the rate‐limiting step in the formation of monounsaturated fatty acids. scd knockout zebrafish showed significantly increased fat accumulation in the liver, leading to hepatic mitochondrial dysfunction and severe cell apoptosis with a typical fatty liver disease phenotype 38 . Omega‐3 desaturase (Fat‐1) of Caenorhabditis elegans is able to convert n‐6 polyunsaturated fatty acids (PUFAs) to n‐3 PUFAs.…”

“…37 The clustered regularly interspaced short palindromic repeats (CRISPR) technique was used to elucidate the function of stearyl-coenzyme-A desaturase (scd) in lipid metabolism. 38 As a common gene knockdown technique, morpholino (MO) inhibits target gene function by blocking the mRNA splicing or translation processes and is especially useful for genes whose homozygous mutants are lethal, like transport protein particle complex 11 (trappc11). 39 Liver phenotype can be rapidly screened in F0 generation after injection; however, its effect gradually weakens as the amount of MO is diluted during the growth of zebrafish embryos.…”

“…For example, deletion of suppressor of cytokine signalling‐1a ( socs1a ) using the transcription activator‐like effector nuclease (TALEN) technique revealed its physiological roles in zebrafish 37 . The clustered regularly interspaced short palindromic repeats (CRISPR) technique was used to elucidate the function of stearyl‐coenzyme‐A desaturase ( scd ) in lipid metabolism 38 . As a common gene knockdown technique, morpholino (MO) inhibits target gene function by blocking the mRNA splicing or translation processes and is especially useful for genes whose homozygous mutants are lethal, like transport protein particle complex 11 ( trappc11 ) 39 .…”

Identification of fish spermatogenic cells through high-throughput immunofluorescence against testis with an antibody set

“…Cell mitotic proliferation is generally indicated by the expression of Pcna, an essential component of the DNA replication machinery ( 33 – 35 ), while meiotic differentiation of spermatogenic cells is indicated by the expression of Sycp3, an essential element of the synaptonemal complex ( 36 ). Previously, these markers have been used selectively in various studies ( 1 , 18 , 37 ), but an integrated analysis of these proteins by immunofluorescence during fish spermatogenesis is lacking.…”