Enhanced degradation of MDM2 by a nuclear envelope component, mouse germ cell-less

Melanocyte Precursors in the Hair Follicle Bulge of Repigmented Vitiligo Skin Are Controlled by RHO-GTPase, KCTD10, and CTNNB1 Signaling

In repigmentation of human vitiligo, the melanocyte (MC) precursors in the hair follicle bulge proliferate, migrate, and differentiate to repopulate the depigmented epidermis. Here, we present a comprehensive characterization of pathways and signals in the bulge that control the repigmentation process. Using biopsies from patients with vitiligo, we have selectively harvested, by laser capture microdissection, MC and keratinocyte precursors from the hair follicle bulge of untreated vitiligo skin and vitiligo skin treated with narrow-band UVB. The captured material was subjected to whole transcriptome RNA-sequencing. With this strategy, we found that repigmentation in the bulge MC precursors is driven by KCTD10, a signal with unknown roles in the skin, and CTNNB1 (encoding β-catenin) and RHO guanosine triphosphatase [RHO GTPase, RHO], two signaling pathways previously shown to be involved in pigmentation biology. Knockdown studies in cultured human MCs of RHOJ, the upmost differentially expressed RHO family component, corroborated with our findings in patients with vitiligo, identified RHOJ involvement in UV response and melanization, and confirmed previously identified roles in melanocytic cell migration and apoptosis. A better understanding of mechanisms that govern repigmentation in MC precursors will enable the discovery of molecules that induce robust repigmentation phenotypes in vitiligo.

1q12 chromosome translocations form aberrant heterochromatic foci associated with changes in nuclear architecture and gene expression in B cell lymphoma

Epigenetic perturbations are increasingly described in cancer cells where they are thought to contribute to deregulated gene expression and genome instability. Here, we report the first evidence that a distinct category of chromosomal translocations observed in human tumours—those targeting 1q12 satellite DNA—can directly mediate such perturbations by promoting the formation of aberrant heterochromatic foci (aHCF). By detailed investigations of a 1q12 translocation to chromosome 2p, in a case of human B cell lymphoma, aberrant aHCF were shown to be localized to the nuclear periphery and to arise as a consequence of long range ‘pairing’ between the translocated 1q12 and chromosome 2 centromeric regions. Remarkably, adjacent 2p sequences showed increased levels of repressive histone modifications, including H4K20me3 and H3K9me3, and were bound by HP1. aHCF were associated to aberrant spatial localization and deregulated expression of a novel 2p gene (GMCL1) that was found to have prognostic impact in diffuse large B cell lymphoma. Thus constitutive heterochromatin rearrangements can contribute to tumourigenesis by perturbing gene expression via long range epigenetic mechanisms.

Emergence of young human genes after a burst of retroposition in primates

The origin of new genes through gene duplication is fundamental to the evolution of lineage- or species-specific phenotypic traits. In this report, we estimate the number of functional retrogenes on the lineage leading to humans generated by the high rate of retroposition (retroduplication) in primates. Extensive comparative sequencing and expression studies coupled with evolutionary analyses and simulations suggest that a significant proportion of recent retrocopies represent bona fide human genes. We estimate that at least one new retrogene per million years emerged on the human lineage during the past ∼63 million years of primate evolution. Detailed analysis of a subset of the data shows that the majority of retrogenes are specifically expressed in testis, whereas their parental genes show broad expression patterns. Consistently, most retrogenes evolved functional roles in spermatogenesis. Proteins encoded by X chromosome−derived retrogenes were strongly preserved by purifying selection following the duplication event, supporting the view that they may act as functional autosomal substitutes during X-inactivation of late spermatogenesis genes. Also, some retrogenes acquired a new or more adapted function driven by positive selection. We conclude that retroduplication significantly contributed to the formation of recent human genes and that most new retrogenes were progressively recruited during primate evolution by natural and/or sexual selection to enhance male germline function.

In humans, retroposition--integration into the genome of DNA reverse transcribed from mRNA--has contributed to the formation of recent functional genes selected to enhance male germline function.

Cullin-based ubiquitin ligases: Cul3-BTB complexes join the family

Cullin-based E3 ligases target substrates for ubiquitin-dependent degradation by the 26S proteasome. The SCF (Skp1-Cul1-F-box) and ECS (ElonginC-Cul2-SOCS box) complexes are so far the best-characterized cullin-based ligases. Their atomic structure has been solved recently, and several substrates have been described in different organisms. In addition to Cul1 and Cul2, higher eucaryotic genomes encode for three other cullins: Cul3, Cul4, and Cul5. Recent results have shed light on the molecular composition and function of Cul3-based E3 ligases. In these complexes, BTB-domain-containing proteins may bridge the cullin to the substrate in a single polypeptide, while Skp1/F-box or ElonginC/SOCS heterodimers fulfill this function in the SCF and ECS complexes. BTB-containing proteins are evolutionary conserved and involved in diverse biological processes, but their function has not previously been linked to ubiquitin-dependent degradation. In this review, we present these new findings and compare the composition of Cul3-based ligases to the well-defined SCF and ECS ligases.

Stage-specific expression of mouse germ cell-less-1 (mGCL-1), and multiple deformations during mgcl-1 deficient spermatogenesis leading to reduced fertility

A mouse homologue of Drosophila germ cell-less, mouse germ cell-less-1 (mgcl-1), is highly expressed in the testis. Previous report revealed that the fertility of the mgcl-1(-/-) male mice is reduced significantly as a result of various morphological abnormalities in the sperm (Kimura et al., 2003). To elucidate the function of mgcl-1 in spermatogenesis, the expression of mGCL-1 in the wild-type testis was examined. Immunohistochemical studies demonstrated that mGCL-1 first appeared in the nuclei of the pachytene spermatocytes at stage VI of the seminiferous epithelium, and existed in those of spermatids until step 8 during spermatogenesis. mGCL-1 was not detectable after step 9 spermatids. The testicular cells and epididymal sperm were further analyzed morphologically using mgcl-1(-/-) mice. In the testis, deformed nuclei first occurred in the pachytene spermatocytes at stage VI, which is consistent with the time of the first appearance of the mGCL-1 protein in the wild-type testis. Abnormal nuclei and acrosomes were found in spermatids after step 5, and nuclei of the spermatids and epididymal sperm were frequently invaginated. In addition, variously deformed sperm such as bent-neck, multi-headed or multi-nucleated sperm were observed in the mgcl-1(-/-) cauda epididymidis. However, several key structures such as the acroplaxome marginal ring (Kierszenbaum et al., 2003), postacrosomal sheath, and posterior ring apparently formed. In addition, MN7 and MN13, essential substances for fertilization that are located in sperm heads, were detectable in the mgcl-1 null sperm. These observations provide important insights into the mechanisms regulating the nuclear architecture and causes of human infertility.