ABSTRACT
Males heterozygous for the t-haplotype form of mouse chromosome 17 preferentially transmit the t-chromosome to their progeny. Several distorter/sterility loci carried on the t-haplotype together impair flagellar function in all spermatozoa whereas the responder, Tcr, rescues t-sperm but not wild-type sperm. Thus, t-sperm have an advantage over wild-type sperm in fertilizing egg cells. We have isolated Tcr by positional cloning and show that it is a member of a novel protein kinase gene family, designated Smok, which is expressed late during spermiogenesis. Smok kinases are components of a signal cascade which may control sperm motility. Tcr has a reduced kinase activity, which may allow it to counterbalance a signalling impairment caused by the distorter/sterility loci. Tcr transgene constructs cause non-mendelian transmission of chromosomes on which they are carried, which leads to sex-ratio distortion when Tcr cosegregates with the Y chromosome.
Subject(s)
Protein Kinases/genetics , Spermatozoa/enzymology , Amino Acid Sequence , Animals , Cloning, Molecular , Gene Expression , Haplotypes , Male , Mice , Molecular Sequence Data , Multigene Family , Protein Kinases/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Sequence Homology, Amino Acid , Signal Transduction , Sperm Motility , Sperm Tail , Spermatogenesis/geneticsABSTRACT
Homologues of the murine Brachyury (T) gene have been cloned from several vertebrates, and are implicated in mesoderm formation and in differentiation of the notochord. In contrast, the roles of the ascidian Brachyury gene may be restricted to presumptive notochord. To understand the evolution of Brachyury genes and their developmental roles, we have searched for homologues in amphioxus, representing the third chordate subphylum and the probable closest relative of the vertebrates. We report the isolation of two amphioxus cDNA clones with clear homology to Brachyury genes, and demonstrate that these derive from separate loci resultant from a recent gene duplication. This finding represents an exception to the emerging consensus of an archetypal prevertebrate genome in amphioxus. The spatial and temporal distribution of Brachyury transcripts during amphioxus development is remarkably similar to vertebrate Brachyury, in presumptive mesoderm, posterior mesoderm and the notochord. Gene expression extends throughout the anteroposterior axis of the notochord, despite the most rostral regions being a more recent specialization; it also persists into larval stages, despite differentiation into contractile tissue. We propose that roles of Brachyury in notochord differentiation are more ancient than roles in mesoderm formation, and that the latter are shared by cephalochordates and all vertebrates.
Subject(s)
Chordata, Nonvertebrate/genetics , Conserved Sequence , DNA-Binding Proteins/genetics , Fetal Proteins/genetics , Mesoderm/physiology , T-Box Domain Proteins , Animals , Base Sequence , DNA Primers/genetics , Molecular Sequence Data , Notochord/physiology , Polymerase Chain Reaction , Sequence Alignment , Vertebrates/geneticsABSTRACT
A total of 1,000 lymphocyte interphase nuclei per proband from 90 females and 138 males age 1 wk to 93 years were analyzed by in situ hybridization for loss of the X and Y chromosomes, respectively. Both sex chromosomes showed an age-dependent loss. In males, Y hypoploidy was very low up to age 15 years (0.05%) but continuously increased to a frequency of 1.34% in men age 76-80 years. In females, the baseline level for X chromosome loss is much higher than that seen for the Y chromosome in males. Even prepubertal females show a rate of X chromosome loss, on the order of 1.5%-2.5%, rising to approximately 4.5%-5% in women older than 75 years. Dividing the female probands into three biological age groups on the basis of sex hormone function (< 13 years, 13-51 years, and > 51 years), a significant correlation of X chromosome loss versus age could clearly be demonstrated in women beyond age 51 years. Females age 51-91 years showed monosomy X at a rate from 3.2% to 5.1%. In contrast to sex chromosomal loss, the frequency of autosomal monosomies does not change during the course of aging: Chromosome 1 and chromosome 17 monosomic cells were found with a constant incidence of 1.2% and 1%, respectively. These data also indicate that autosome loss in interphase nuclei is not a function of chromosome size.
Subject(s)
Aging/genetics , Sex Chromosomes/genetics , Adolescent , Adult , Aged , Aged, 80 and over , Child , Child, Preschool , Chromosomes, Human, Pair 1 , Chromosomes, Human, Pair 17 , DNA Probes , Female , Humans , In Situ Hybridization , Infant , Infant, Newborn , Interphase , Male , Middle AgedABSTRACT
The mouse Brachyury (T) gene is required for differentiation of the notochord and formation of mesoderm during posterior development. Homozygous embryos lacking T activity do not develop a trunk and tail and die in utero. The T gene is specifically expressed in notochord and early mesoderm cells in the embryo. recent data have demonstrated that the T protein is localized in the cell nucleus and specifically binds to a palindrome of 20 bp (the T site) in vitro. We show that the T protein activates expression of a reporter gene in HeLa cells through binding to the T site. Thus T is a novel tissue-specific transcription factor. It consists of a large N-terminal DNA binding domain (amino acids 1-229) and two pairs of transactivation and repression domains in the C-terminal protein half. T can also transactivate transcription through variously oriented and spaced T sites, a fact that may be relevant in the search for genes controlled by T protein and important in mesoderm development.
