title: Extralenticular expression of Xenopus laevis alpha-, beta-, and gamma-crystallin genes.
abstract: OBJECTIVE
  Extralenticular expression of alpha- and beta-crystallin genes has been demonstrated in mammals and expression of gamma-crystallin genes has been shown in Xenopus laevis. To determine a possible correlation between lens determination and crystallin gene expression, the site of expression of (a member of) the alpha-, beta-, and gamma-crystallin gene families was observed before and during lens formation in X. laevis.
  
  
  METHODS
  The partial complementary DNAs (cDNAs) of alpha A- and beta A4-crystallin and a gamma-crystallin were cloned from an X. laevis lens cDNA library. The corresponding antisense RNAs were used to analyze the expression of these genes during X. laevis development by wholemount in situ hybridization.
  
  
  RESULTS
  Expression of the beta A4- and gamma-crystallin (but not alpha-crystallin) genes could first be detected in the animal cap of the X. laevis gastrula. The beta A4- and gamma-crystallin messengers were also found in the first stage of lens development, when the ectodermal tissue overlying the optic vesicle thickens to form the lens placode. alpha A-crystallin messenger RNAs were only detectable when the lens epithelial cells were formed.
  
  
  CONCLUSIONS
  In contrast to observations in most vertebrates, expression of the beta A4- and gamma-crystallin genes was observed to precede that of the alpha A-crystallin gene during lens development of X. laevis, reflecting the determination that in amphibians, the (presumptive) fiber cells are formed before the epithelial cells, whereas in vertebrates, the order is reversed. Expression of beta A4- and gamma-crystallin genes in the ectodermal tissue of the X. laevis gastrula shows that these genes are expressed when this tissue gains competence for lens formation.
authors.affiliation: Department of Molecular Biology, University of Nijmegen, The Netherlands.
authors.forename: G A
authors.initials: GA
authors.lastname: Brunekreef
authors.forename: S T
authors.initials: ST
authors.lastname: van Genesen
authors.forename: O H
authors.initials: OH
authors.lastname: Destrée
authors.forename: N H
authors.initials: NH
authors.lastname: Lubsen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D003459:Crystallins / Q000096:biosynthesis* / Q000235:genetics; D018076:DNA, Complementary / Q000032:analysis; D004625:Embryo, Nonmammalian / Q000378:metabolism*; D015870:Gene Expression; D015723:Gene Library; D017403:In Situ Hybridization; D007908:Lens, Crystalline / Q000196:embryology / Q000378:metabolism*; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis / Q000196:embryology / Q000378:metabolism*
chemical_list: D003459:Crystallins; D018076:DNA, Complementary; D012333:RNA, Messenger