The E3 ubiquitin ligase Cullin 4A regulates meiotic progression in mouse spermatogenesis

Abstract

The Cullin-RING ubiquitin-ligase CRL4 controls cell cycle, DNA damage checkpoint response and ensures genomic integrity. Inactivation of the Cul4 component of the CRL4 E3 ligase complex in Caenorhabditis elegans by RNA interference results in massive mitotic DNA re-replication in the blast cells, largely due to failed degradation of the DNA licensing protein, CDT-1, and premature spermatogenesis. Here we show that inactivation of Cul4a by gene-targeting in mice only affected male but not female fertility. This male infertility phenotype resulted from a combination of decreased spermatozoa number, reduced sperm motility and defective acrosome formation. Agenesis of the mutant germ cells was accompanied by increased cell death in pachytene/diplotene cells with markedly elevated levels of phospho-p53 and CDT-1. Despite apparent normal assembly of synaptonemal complexes and DNA double strand break repair, dissociation of MLH1, a component of the late recombination nodule, was delayed in Cul4a−/− diplotene spermatocytes, which potentially led to subsequent disruptions in meiosis II and spermiogenesis. Together, our study revealed an indispensable role for Cul4a during male germ cell meiosis.

Essential role of the CUL4B ubiquitin ligase in extra-embryonic tissue development during mouse embryogenesis

“…However, an emerging mechanism that distinguishes the two CUL4 proteins is the nonoverlapping expression pattern of CUL4A and CUL4B in specific tissues and organs during development. For example, Cul4b expression is silenced in the pachytenediplotene stages of meiotic prophase, accounting for the reproductive defects and male infertility of the Cul4a −/− mice [14]. Another difference is the predominant cytoplasmic vs nuclear distribution of CUL4A and CUL4B, respectively, suggesting another mechanism of substrate preference between the two CUL4 proteins [29,30], although a subpopulation of CUL4A also resides in the www.cell-research.com | Cell Research Liren Liu et al 1267…”

“…We set out to investigate whether the lethality of Cul4b −/Y mice results from the differential expression patterns of the two CUL4 proteins, which were recently demonstrated as the cause of the meiotic defects in Cul4a −/− male mice [13,14]. In unhatched E3.5-4.0 blastocysts, both CUL4 proteins were detected in the inner cell mass (ICM) as well as in trophoblast (TB) cells (open arrowheads, Figure 4A-4D).…”

“…However, primary mouse embryonic fibroblasts preferentially utilize CUL4A to restrict p21 levels [12], suggesting context-dependent degradation of p21 by the two CUL4 ubiquitin ligases. Cul4a null mice are viable and display no gross phenotypic abnormalities throughout their lifespan except for meiotic defects in male mice [12][13][14]. Despite the largely overlapping functions of CUL4A and CUL4B, recent studies also revealed distinct roles for the two CUL4 family members in DNA-damage response, male meiosis, and response to environmental toxins [12][13][14][15].…”

“…Cul4a null mice are viable and display no gross phenotypic abnormalities throughout their lifespan except for meiotic defects in male mice [12][13][14]. Despite the largely overlapping functions of CUL4A and CUL4B, recent studies also revealed distinct roles for the two CUL4 family members in DNA-damage response, male meiosis, and response to environmental toxins [12][13][14][15]. While CUL4B compensates for the loss of CUL4A [12], CUL4A expression, which is unaffected by CUL4B mutations [16], is apparently unable to rescue the neuronal and developmental deficiencies found in CUL4B patients with XLMR.…”

CUL4B ubiquitin ligase in mouse development: A model for human X-linked mental retardation syndrome?

“…CUL4A and CUL4B assemble structurally similar E3 complexes through binding to an adaptor protein (DDB1) and a substrate receptor protein (DCAF) at the N-terminus, and a RING protein RBX1 at the C-terminus (Figure 1), and share functional redundancy in targeting substrates such as p21 and Cdt1 for ubiquitination and degradation [1,2]. The Cul4a-null mice are viable and display no abnormal development and growth phenotypes, likely due to functional compensation from Cul4b [4,5]. The only phenotype associated with Cul4a abrogation is the reproductive defects seen with male but not female mice, resulting from differential non-overlapping expression patterns of the two Cul4 genes during male meiosis [6].…”