X-chromosome inactivation may explain the difference in viability of XO humans and mice.

Only about 1% of human XO conceptuses survive to birth and these usually have the characteristics of Turner's syndrome, with a complex and variable phenotype including short stature, gonadal dysgenesis and anatomical defects. Both the embryonic lethality and Turner's syndrome are thought to be due to monosomy for a gene or genes common to the X and Y chromosomes. These genes would be expected to be expressed in females from both active and inactive X chromosomes to ensure correct dosage of gene product.

Conservation of position and exclusive expression of mouse Xist from the inactive X chromosome.

X-chromosome inactivation in mammals is a regulatory phenomenon whereby one of the two X chromosomes in female cells is genetically inactivated, resulting in dosage compensation for X-linked genes between males and females. In both man and mouse, X-chromosome inactivation is thought to proceed from a single cis-acting switch region or inactivation centre (XIC/Xic). In the human, XIC has been mapped to band Xq13 (ref.

The ZFY gene family in humans and mice.

For several years, ZFY (zinc finger gene on the Y chromosome) was considered the best candidate for the human testis-determining gene TDF. This gene and its close relatives have been intensely studied in the hope of understanding the molecular biology of sex determination, particularly in humans and mice. Now that there is overwhelming evidence that ZFY and TDF are distinct loci, we are left with a large body of data, and a question: what do these genes really do?

Zfa is an expressed retroposon derived from an alternative transcript of the Zfx gene.

ZFY, a gene on the Y chromosome encoding a zinc finger protein, has been proposed as a candidate for the human testis determining gene. Sequences related to ZFY, called ZFX, are present on the X chromosome of a wide range of placental mammals. Unlike most mammals the mouse has four genes homologous to ZFY; two on the Y chromosome, Zfy-1 and Zfy-2, an X-linked gene, Zfx, and an autosomal gene, Zfa.

Isolation of a human cytochrome P-450 reductase cDNA clone and localization of the corresponding gene to chromosome 7q11.2.

We have isolated and sequenced cDNA clones that code for rat and human NADPH-dependent cytochrome P-450 reductase. The cDNA coding for the human protein was used to analyse, by Southern blot hybridization, DNA isolated from a panel of 8 independent human-rodent somatic cell hybrids. The results indicate that cytochrome P-450 reductase is encoded by a single gene (POR) located on human chromosome 7(pter-q22).

Chromosomal localization of zinc finger protein genes in man and mouse.

We have determined the mouse and human chromosomal location of a gene (Zfp-3) that codes for a protein that contains potential DNA zinc-binding fingers. An analysis of the segregation of restriction fragment length polymorphisms in recombinant inbred strains and in an interspecific backcross demonstrated that Zfp-3 is located on mouse chromosome 11. Zfp-3 is very closely linked to the Trp53-1 locus but unlinked to another finger protein gene Zfp-4 located on mouse chromosome 8.

Breast-feeding among the urban poor in southern Brazil: reasons for termination in the first 6 months of life.

A study of breast-feeding practices over the first 6 months of life among a cohort of urban poor infants in southern Brazil indicated that the median duration of breast-feeding was 18 weeks, and at 6 months 41% of the infants were still being breast-fed. The duration of breast-feeding was significantly associated with the following: the infant's sex, mother's colour, type of first feed, timing of the first breast-feed, breast-feeding regimen and frequency of breast-feeding at 1 month, and the use of hormonal contraceptives by the mother. The following were significant risk factors for early termination of breast-feeding: the infant's sex, type of first feed, use of supplementary feeds, frequency of breast-feeding, feeding regimen, weight-for-age, and weight-for-age after controlling for birth weight.

Infant mortality in southern Brazil: a population based study of causes of death.

The causes of 215 infant deaths occurring in a population based cohort of 5914 infants from southern Brazil were determined. Perinatal problems were responsible for 43% of these deaths and infectious diseases for 32%. In the group who died of infectious diseases, respiratory infections and diarrhoea were equally important, each accounting for 12% of all deaths.

Infant feeding practices in Kenya, Mexico and Malaysia. The rarity of the exclusively breast-fed infant.

Infant feeding practices of 6149 mothers in Kenya, Mexico and Malaysia are reported. A high proportion of mothers initiated breast-feeding in each country regardless of social class. Most Kenyan mothers continued to breast-feed for at least 12 months.

Historical review of the changing pattern of infant feeding in developing countries: the case of Malaysia, the Caribbean, Nigeria and Zaire.

Prolonged lactation and early supplementation have been traditional practices among low-income mothers in Malaysia, the Caribbean, Nigeria and Zaire. Early supplementation is still the norm but there have been some substantial changes in the types of supplement offered. Thus, except in Zaire, there is now widespread use of processed milks as supplements for very young infants.

Isolation and sequence of a human cytochrome P-450 cDNA clone.

A previously reported cDNA clone [pP450(1)] coding for a phenobarbital-inducible cytochrome P-450 variant of rat liver microsomal membranes, designated P-450e(U.C.), was used as a specific hybridization probe to screen a human liver cDNA library.

Interventions for the control of diarrhoeal diseases among young children: prevention of low birth weight.

The effect of low birth weight (LBW) on diarrhoea morbidity and mortality is analysed and interventions to increase birth weights are reviewed. Birth weight is a major determinant of infant mortality and, in developed countries at least, its effect on neonatal mortality is independent of socioeconomic status. We have located no satisfactory data on LBW as a determinant of diarrhoea mortality or morbidity.

Cloning and sequence analysis of a rat liver cDNA coding for a phenobarbital-inducible microheterogenous cytochrome P-450 variant: regulation of its messenger level by xenobiotics.

A rat liver cDNA library was prepared from total polyribosomal poly(A)+ RNA extracted from phenobarbital-treated animals. A cDNA clone coding for a phenobarbital-inducible cytochrome P-450 (PB P-450) was identified by differential colony hybridization to cDNAs synthesized from liver poly(A)+RNAs isolated from phenobarbital-treated rats for positive selection and cDNAs from either untreated rats or beta-naphthoflavone-treated rats as negative controls, followed by hybrid-selected translation and analysis of the translation products by immunoprecipitation. As the cloning and screening strategies involve no prior enrichment for specific mRNAs, they also permit the identification of sequences coding for phenobarbital-induced proteins other than cytochromes P-450.