BIMM 110    Lecture 13

TEXTBOOK:   Strachan and Read, Chapter 10, pp. 305-306
                          Pasternak; Chaper 11: p.344

 SLIDES

A. Genetic aspects of sex determination and development

1. Primary sex determination 

- sex chromosomes X and Y
- gonadal sex determination - primary sex determination
- the undifferentiated gonad; Wolffian and Mullerian ducts
- testis determining factor (TDF)
- Mullerian inhibitor (anti-Mullerian hormone, AMH)
- Leydig and Sertoli cells in testis; follicular and theca cells in ovary

2. Secondary sex characteristics

- steroid hormones and their receptors;
- single gene effects on sexual development:
                 defects in biosynthetic pathways for androgens, etc.;
                 defective or missing receptors

3. The sex ratio

- a Punnett square predicts a 50:50 ratio; in reality there is a slight excess of male births

4. Pseudohermaphroditism (see below)

 B. Chromosomal anomalies in sexual development

- Turner Syndrome and related disorders (45,X); gonadal dysgenesis, generally sterile; short stature
heart problems, kidney problems or thyroid problems are the most frequent associated health problems; IQ is in the normal range
occurance: in 1/2000 - 1/2500 female live births,

- Klinefelter Syndrome (47,XXY) Barr body positive, phenotypic males with possibility of some morphological abnormalities: enlarged breasts, sparse facial and body hair; always sterile
Many men live out their lives without ever even suspecting that they have an additional X chromosome. " I never refer to newborn babies as having Klinefelter's, because they don't have a syndrome," said Arthur Robinson, M.D., a pediatrician at the University of Colorado Medical School in Denver
occurance: in 1/500 male births

- the XYY "syndrome"

- - the triple X syndrome   "Triple X girls more frequently than other girls have a delayed development in motor function, speech, and maturation, though this does not make them patients or call for special treatment".

- Hermaphrodites and pseudohermaphrodites
"True hermaphroditism requires the presence of both ovarian (female) and testicular (male) reproductive tissue and is relatively rare and poorly understood. Pseudohermaphroditism is more common and from a medical standpoint hermaphroditism suggests two factors: ambiguous external genitalia that may not match the genetic make-up of the person (example: female genitalia in an XY, genetically male, individual.)"
(further discussion in lecture on Y chromosome)

-
 
 

C. X chromosome inactivation

1. Phenomenology

- Barr body
- the Lyon hypothesis; dosage compensation; random X-inactivation in development;

- mosaicism in females with genetic heterozygosity on X chromosome

- X chromosome-autosome translocations: intact X is generally inactive
        relevance to expression of X-linked, recessive mutations

- parts of the X chromosome are not inactivated

- the pseudoautosomal region of X and Y chromosomes (PAR);
- chiasma formation between X and Y chromosomes in male meiosis
- an increasing number of genes are found not to be inactivated; examples: STS, ZFX,

- X inactivation and DNA methylation: what comes first?
           methylation-sensitive and insensitive restriction enzymes used in the study of DNA methylation

- relationship to the more general problem of imprinting ? (Lecture 17)

 2. the XIST gene and its transcript

        - expression from the inactive X chromosome
        - transcript (~16 kb) is not translatable into peptide (no large ORFs)
        - the XIST transcript is associated with the Barr body

- expression in early XX embryos in relation to X inactivation: detection by PCR

- transgenic mice with the Xist locus expressed on an autosome

- more complications: there is also a TSIX gne/transcript with an antisense orientation

- the X inactivation center (XIC)

3. reactivation of X linked genes in somatic cell hybrids

 A. Historical

 - Brown, C.J. and Willard, H.F. (1990). Localization of a gene that escapes inactivation to the X chromosome proximal short arm: Implications for X inactivation. Am. J. Hum. Genet. 46, 273-279.
- Cedar, H. (1988). DNA methylation and gene activity. Cell 53, 3-4.
- Chapman, V.M., Kratzer, P.G., Siracusa, L.D., Quarantillo, B.A., and Liskay, R.M. (1982). Evidence for DNA modification in the maintenance of X-chromosome inactivation of adult mouse tissues. Proc. Nat. Acad. Sci. USA 79, 5357-5361.
- Charlesworth, B. (1991). The evolution of sex chromosomes. Science 251, 1030-1033.
- De la Chapelle, A., Page, D.C., Brown, L., Kaski, U., Parvinen, T., and Tippett, P.A. (1986). The origin of 45,X males. Am. J. Hum. Genet. 38, 330-340.
- Dynan, W.S. (1989). Understanding the molecular mechanism by which methylation influences gene expression. Trends in Genet. 5,
- Grant, S.G., and Chapman, V.M. (1988). Mechanisms of X-chromosome regulation. Annu. Rev. Genet. 22, 199-233.
- Jacobs, P.A., and Migeon, B.R. (1989). Studies of X-chromosome inactivation in trisomies. Cytogenet. Cell Genet. 50, 75-77.
- Juberg, R.C., Holliday, D.J., and Hennessy, V.S. (1990). Familial sex chromosomal mosaicism. Am. J. Med. Genet. 37, 15-17.
- Kaslow, D.C., and Migeon, B.R. (1987). DNA methylation stabilizes X chromosome inactivation in eutherians but not in marsupials: evidence for multistep maintenance of mammalian X dosage compensation. Proc. Natl. Acad. Sci. USA 84, 6210-6214.
- Lock,L., Melton,D.W., Caskey,C.T. and Martin,G.R. (1986). Methylation of the mouse hprt gene differs on the active and inactive X chromosomes. Molec.Cell.Biol. 6:906-924.
- Lyon, M.F. (1991). The quest for the X-inactivation centre. TIG 7, 69-70.
- Mann, J.R., and Lovell-Badge, R.H. (1988). Two maternally derived X chromosomes contribute to parthenogenetic inviability. Development 104, 129-136.
- Martin,G. (1982). X-chromosome inactivation in mammals. Cell 29:721-724.
- Mohandas, T., Geller, R.L., Yen, P.H., Rosendorff, J., Bernstein, R., Yoshida, A., and Shapiro, L.J. (1987). Cytogenetic and molecular studies on a recombinant human X chromosome: implications for the spreading of X chromosome inactivation. Proc. Natl. Acad. Sci. USA 84, 4954-4958.
- Mohandas, T., Shapiro, L.J., Sparkes, R.S., and Sparkes, M.C. (1979). Regional assignment of the steroid sulfatase-X-linked ichthyosis locus: Implications for a noninactivated region on the short arm of the human X chromosome. Proc. Nat. Acad. Sci. USA 76, 5779-5783.
- Mohandas, T., Sparkes, R.S., and Shapiro, L.J. (1981). Reactivation of an inactive human X chromosome: Evidence for X inactivation by DNA methylation. Science 211, 393-396.
- Solter, D. (1988). Differential imprinting and expression of maternal and paternal genomes. Annu. Rev. Genet. 22, 127-146.
- Swain, J.L., Stewart, T.A., and Leder, P. (1987). Parental legacy determines methylation and expression of an autosomal transgene: A molecular mechanism for parental imprinting. Cell 50, 719-727.
- Takagi, N. and Abe, K. (1990). Detrimental effects of two active X chromosomes on early mouse development. Development 109, 189-201.
-Brown, C.J., Hendrich, B.D., Rupert, J.L., Lafrenière, R.G., Xing, Y., Lawrence, J., and Willard, H.F. (1992). The human XIST gene: Analysis of a 17 kb inactive X-specific RNA that contains conserved repeats and is highly localized within the nucleus. Cell 71, 527-542.
-Freije, D., Helms, C., Watson, M.S., and Donis-Keller, H. (1992). Identification of a second pseudoautosomal region near the Xq and Yq telomeres. Science 258, 1784-1787.
-Kay, G.F., Penny, G.D., Patel, D., Ashworth, A., Brockdorff, N., and Rastan, S. (1993). Expression of Xist during mouse development suggests a role in the initiation of X chromosome inactivation. Cell 72, 171-182.
-Lyon, M.F. (1992). Some milestones in the history of X-chromosome inactivation. Annu. Rev. Genet. 26, 17-28.
-Mandel, J.-L., Monaco, A.P., Nelson, D.L., Schlessinger, D., and Willard, H. (1992b). Genome analysis and the human X chromosome. Science 258, 103-109.
-Tan, S.-S., Williams, E.A., and Tam, P.P.L. (1993). X-chromosome inactivation occurs at different times in different tissues of the post-implantation mouse embryo. Nature Genet. 3, 170-174.
-Zinn, A.R., Page, D.C., and Fisher, E.M.C. (1993). Turner syndrome: The case of the missing sex chromosome. Trends Genet. 9, 90-93.

 B. Recent

 - Buzin, C.H., Mann, J.R., and Singer-Sam, J. (1994). Quantitative RT-PCR assays show Xist RNA levels are low in mouse female adult tissue, embryos and embryoid bodies. Development 120, 3529-3536.
- Courtier, B., Heard, E., and Avner, P. (1995). Xce haplotypes show modified methylation in a region of the active X chromosome lying 3' to Xist. Proc. Natl. Acad. Sci. USA 92, 3531-3535.
- Disteche, C.M. (1995). Escape from X inactivation in human and mouse. TIG 11, 17-22.
- Hansen, R.S., Canfield, T.K., and Gartler, S.M. (1995). Reverse replication timing for the XIST gene in human fibroblasts. Hum. Mol. Genet. 4, 813-820.
- Jeppesen, P. and B. M. Turner. 1993. The inactive X chromosome in female mammals is distinguished by a lack of histone H4 acetylation, a cytogenetic marker for gene expression. Cell 74:281-289.
- Kay, G. F., S. C. Barton, M. A. Surani, and S. Rastan. 1994. Imprinting and X chromosome counting mechanisms determine Xist expression in early mouse development. Cell 77:639-650.
- Migeon, B.R., Luo, S., Jani, M., and Jeppesen, P. (1994). The severe phenotype of females with tiny ring X chromosomes is associated with inability of these chromosomes to undergo X inactivation. Am. J. Hum. Genet. 55, 497-504.
- Migeon, B. R. 1994. X-chromosome inactivation: molecular mechanisms and genetic consequences. Trends in Genet. 10:230-235.
- Miller, A.P., Gustashaw, K., Wolff, D.J., Rider, S.H., Monaco, A.P., Eble, B., Schlessinger, D., Gorski, J.L., Van Ommen, G.-J., Weissenbach, J., and Willard, H.F. (1995). Three genes that escape X chromosome inactivation are clustered within a 6 Mb YAC contig and STS map in Xp11.21-p11.22. Hum. Mol. Genet. 4, 731-739.
- Torchia, B.S., Call, L.M., and Migeon, B.R. (1994). DNA replication analysis of FMRI, XIST, and factor 8C loci by FISH shows nontranscribed X-linked genes replicate late. Am. J. Hum. Genet. 55, 96-104.

- Coffee, B., Zhang, F., Warren, S.T., and Reines, D. (1999). Acetylated histones are associated with FMR1 in normal but not fragile X-syndrome cells.  Nat.Genet. 22, 98-101.
- Constancia, M., Pickard, B., Kelsey, G., and Reik, W. (1998). Imprinting mechanisms.  Genome Res. 8, 881-900.
- Duthie, S.M., Nesterova, T.B., Formstone, E.J., Keohane, A.M., Turner, B.M., Zakian, S.M., and Brockdorff, N. (1999). Xist RNA exhibits a banded localization on the inactive X chromosome and is excluded from autosomal material in cis.  Hum.Mol.Genet. 8, 195-204.
- Kelley, R.L., and M.I. Kuroda (2000) The role of chromosomal RNAs inmarking the X for dosage compensation. Curr. Opin. Genet. & Developm. 10: 555-561.
- Willard, H.F., and Carrel, L. (2001) Making sense (and antisense) of the X inactivation center PNAS 98: 10025-10027