Background: Ventral specification is regulated by Smad1-, Smad5-, and/or Smad9-mediated bone morphogenetic protein (BMP) signaling. Results: Double knockdown instead of single knockdown of smad1 and smad9 induces dorsalization, which cannot be rescued by smad5 overexpression. Conclusion: smad1 and smad9 act redundantly and downstream of smad5 to mediate ventral specification. Significance: The regulation network and cooperative roles of BMP R-Smads in early development are clarified.
Omega-3 long-chain polyunsaturated fatty acid (n-3 LC-PUFA), especially eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are essential nutrients for human health. However, vertebrates, including humans, have lost the abilities to synthesize EPA and DHA de novo, majorly due to the genetic absence of delta-12 desaturase and omega-3 desaturase genes. Fishes, especially those naturally growing marine fish, are major dietary source of EPA and DHA.
The Gal4/upstream activating sequence (UAS) system is a powerful genetic tool for the temporal and spatial expression of target genes. In this study, the dynamic activity of the Gal4/UAS system was monitored in zebrafish throughout the entire lifespan and during germline transmission, using an optimized Gal4/UAS, KalTA4/4xUAS, which is driven by two muscle-specific regulatory sequences. We found that UAS-linked gene expression was transcriptionally amplified by Gal4/UAS during early developmental stages and that the amplification effects tended to weaken during later stages and even disappear in subsequent generations. In the F2 generation, the transcription of a UAS-linked enhanced green fluorescent protein (EGFP) reporter was transcriptionally silent from 16 days post-fertilization (dpf) into adulthood, yet offspring of this generation showed reactivation of the EGFP reporter in some strains. We further show that the transcriptional silencing and reactivation of UAS-driven EGFP correlated with the DNA methylation levels of the UAS regulatory sequences. Notably, asymmetric DNA methylation of the 4xUAS occurred in oocytes and sperm. Moreover, the paternal and maternal 4xUAS sequences underwent different DNA methylation dynamics after fertilization. Our study suggests that the Gal4/UAS system may represent a powerful tool for tracing the DNA methylation dynamics of paternal and maternal loci during zebrafish development and that UASspecific DNA methylation should be seriously considered when the Gal4/UAS system is applied in zebrafish.
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.
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