No abstract

Translocation is one of the most frequently occurring human chromosomal aberrations. Balanced carriers usually manifest no phenotype but experience problems with reproduction. These include infertility, recurrent abortion, and offspring with chromosomal imbalance. The constitutional t(11;22)(q23;q11) is a balanced translocation between chromosomes 11 and 22, with breakpoints at bands 11q23 and 22q11. It is the only known recurrent non-Robertsonian translocation and represents a good model for studying translocations in humans (1). The recurrent nature of this translocation prompted us to examine t(11;22) breakpoints for a specific genomic structure. The analysis of many unrelated t(11;22) cases revealed that the breakpoints occur within palindromic AT-rich repeats (PATRRs) on 11q23 and 22q11 (PATRR11 and PATRR22) (2-4). The majority of the breakpoints are localized at the center of the PATRRs, suggesting that the center of the palindrome is susceptible to double-strand breaks (DSBs), thereby inducing illegitimate chromosomal rearrangement (3,5). Recent findings of PATRRlike sequences at the breakpoints of other translocations support the possibility that palindromemediated chromosomal translocation is a general pathway for human genomic rearrangements (6-8).The PATRR11 is variable in size in normal healthy individuals ( Fig. 1 and table S1). The most common allele is a ~450-base pair (bp) PATRR11 (L-PATRR11) that forms a nearly perfect palindrome (5). Several types of short variants were identified (S-PATRR11) that appear to be derived from the longer version primarily by deletion near the symmetric center of the palindromic structure. We can classify the S-PATRR11s into four groups. The most frequent 350-bp variant, S1-PATRR11, has a 50-bp deletion at both of the palindromic arms but still remains completely symmetrical. S2-PATRR11 has an asymmetric deletion at its center, but the new center manifests a symmetric palindrome. S3-PATRR11 does not possess palindromic features by virtue of a deletion at the center of the palindrome. We identified a rare 434-bp S-PATRR11, which sustained an asymmetric central deletion followed by the insertion of an ATrich sequence of unknown origin (S4-PATRR11). We also identified another rare allele with a duplication of the proximal arm, which constitutes a 603-bp asymmetric palindrome (EL-PATRR11). On the basis of the palindrome-mediated mechanism of the translocation, it is reasonable to hypothesize that the polymorphism of the PATRR11 could affect the frequency of de novo t(11;22) translocations.

Palindromic sequences are dispersed in the human genome and may cause chromosomal translocations in humans. They constitute unsequenced gaps in the human genome because of their resistance to PCR amplification, cloning into vectors, and sequencing. We have overcome these difficulties by using a combination of optimized PCR conditions, cloning in a recombinationdeficient E. coli strain, and RNA polymerases in sequencing. Using these methods, we analyzed a palindromic AT-rich repeat (PATRR) in the neurofibromatosis type 1 (NF1) gene on chromosome 17 (17PATRR). The 17PATRR manifests a size polymorphism due to a highly variable length of (AT) n dinucleotide repeats within the PATRR. 17PATRRs can be categorized into two types: a longer one that comprises a nearly or completely perfect palindrome, and a shorter one that represents its deleted asymmetric derivative. In vitro analysis shows that the longer 17PATRR is more likely to form a cruciform structure than the shorter one. Two reported t(17;22)(q11;q11) patients with NF1, whose breakpoints were identified within the 17PATRR, have translocations that are derived from perfect or nearly perfect palindromic alleles. This implies that the symmetric structure of a PATRR can induce a translocation. We identified conserved PATRRs within the NF1 gene in great apes and similar inverted repeats in two Old World monkeys, but not in New World monkeys or other mammals. This indicates that the palindromic region appeared approximately 25 million years ago and elongated during primate evolution. Although such palindromic regions are usually unstable and disappear rapidly due to deletion, the 17PATRR in the NF1 gene was stably conserved during evolution for reasons that are still unknown.

Because our experimental system is a good model of renal transplantation from brain dead or living human donors, our data may be useful for elucidating the pathologic processes involved and for identification of novel markers for graft dysfunction of renal transplantation.

Heat shock transcription factor on Y (HSFY) is located in one of three candidate regions for azoospermic factor (AZF), AZFb on the Y chromosome. We and others have already revealed that some azoospermic males are missing the regions of the Y chromosome including HSFY. Previously, we showed that murine HSFY-like sequence [mHSFYL (Riken cDNA 4933413G11Rik)], which is the mouse orthologue of HSFY, is exclusively expressed in testis. The sequences encoding the presumed DNA-binding domain in HSFY and mHSFYL were found in other mammals such as dogs, cows and chickens. To elucidate mHSFYL expression in the testes in detail, we carried out in situ hybridization. mHSFYL was predominantly expressed in round spermatids. Furthermore, we clarified the intracellular distribution of mHSFYL in COS1 cells with HA- or GFP-tagged proteins. Both HA-mHSFYL and GFP-mHSFYL were located in the nucleus. Our results suggest that HSFY/mHSFYL may have evolutionarily conserved functions for spermatogenesis.