Sexually Dimorphic Neurocalcin Expression in theDeveloping Zebra Finch TelencephalonSean L. Veney,1,2Camilla Peabody,1,2George W. Smith,3Juli Wade1,2,41Neuroscience Program, Michigan State University, East Lansing, Michigan 488242Department of Psychology, Michigan State University, East Lansing, Michigan 488243Departments of Animal Science & Physiology, Michigan State University,East Lansing, Michigan 488244Department of Zoology, Michigan State University, East Lansing, Michigan 48824Received 6 January 2003; accepted 3 April 2003ABSTRACT: Differential display RT-PCR wasused on RNA isolated from the zebra finch telencepha-lon to identify gene products potentially involved in itsdevelopment, including the sexually dimorphic nucleiresponsible for song learning and production. A cDNAidentified only in juvenile females was cloned and se-quenced. It shares homology with neurocalcin, a calciumbinding protein. Northern blots indicated three neuro-calcin species. A 10.6 kb transcript was present in malesand most females throughout development and in adult-hood. Smaller 6.2 and 3.3 kb species were detected al-most exclusively in females and primarily between post-hatching days 18 –25. In situ hybridization, using aprobe that identified all three mRNA species, indicated abroad distribution in the telencephalon of both sexes,with particularly high levels in the song nucleus RA.Across regions examined, neurocalcin expression wasenhanced in females compared to males, probably re-flecting the presence of the two smaller transcripts.However, within RA, neurocalcin expression was statis-tically equivalent between the sexes. These data indicatethat calcium signaling via neurocalcin may be involvedin telencephalic development, but suggest that sexuallydimorphic expression of this gene exists on a level toogeneral to specifically regulate masculine or femininedevelopment of song control regions. Neurocalcin might:broadly influence functional differentiation, includingareas that are not morphologically distinct between thesexes; be a benign consequence of general dimorphisms,such as those due to sex chromosomes; or involve acompensatory mechanism, which allows function of thejuvenile female telencephalon to equal that of males,despite fundamental physiological differences.© 2003Wiley Periodicals, Inc. J Neurobiol 56: 372–386, 2003Keywords: calcium binding; sex difference; differentialdisplay; neural development; songbirdINTRODUCTIONIn many species of vertebrates, early gonadal secre-tions organize sex differences in neural morphologyand/or function (Feder, 1981; Yahr, 1988; Meisel andSachs, 1994). These differences, particularly in brainareas important for reproduction, often relate to thefrequency with which masculine or feminine behav-iors are displayed (Cooke et al., 1998; Madeira andLieberman, 1995). However, not all sex differencescan easily be explained by the actions of gonadalsteroids (Arnold, 1997; Wade, 2001; Carruth et al.,2002). In addition, sex differences in morphologyneed not always bias function; differences in thebrains of males and females on a cellular (or molec-ular) level may in some cases even facilitate similarCorrespondence to: S. Veney ([email protected]).Contract grant sponsor: NIH; contract grant number: MH55488(J.W.).Contract grant sponsor: NSF; contract grant number: DBI-0001973 (S.V.).© 2003 Wiley Periodicals, Inc.DOI 10.1002/neu.10246372function of brain regions despite inherent differencesbetween the sexes (De Vries and Boyle, 1998).The development of sex differences in the brainand behavior of zebra finches is particularly intriguing(Balthazart and Adkins-Regan, 2002). Song learningand production are controlled by a series of intercon-nected regions within the telencephalon. Area X andthe lateral portion of the magnocellular nucleus of theanterior neostriatum (lMAN) are involved in songlearning (Bottjer et al., 1984; Scharff and Nottebohm,1991). The high vocal center (HVC) and robust nu-cleus of the archistriatum (RA) form the motor path-way for song production (Nottebohm et al., 1976;Simpson and Vicario, 1990). HVC projects to RA,which in turn projects to the tracheosyringeal portionof the hypoglossal nucleus (nXIIts), which containsmotoneurons that innervate the vocal organ, or syrinx(Nottebohm et al., 1976). Sexual dimorphisms exist ata number of levels within this system (Arnold, 1992;Wade, 1999). For example, only males sing, and thevolumes of HVC and RA as well as the soma size andnumber of neurons within these nuclei are greater inmales than in females. The projection from HVC toRA is more robust in males than in females. And AreaX, which is easily identified in males, is not visible infemales using standard Nissl stains. These neural di-morphisms, which are assumed to permit song pro-duction in males and inhibit it in females, developbetween approximately 1 week and 2 months of age,with the most striking rate of differentiation occurringbetween days 15 and 35 posthatching (Bottjer et al.,1985; Kirn and DeVoogd, 1989; Nixdorf-Bergweiler,1996).Similar to many other sexually dimorphic systems,both the structure and function of the zebra finch songsystem can be permanently modified by steroid hor-mones. For example, treatment of females with estra-diol in the first few weeks after hatching can partiallymasculinize several morphological features of theneural song system as well as the capacity for femalesto sing in adulthood (Gurney, 1981, 1982; Nordeen etal., 1986; Simpson and Vicario, 1991a, b; Grishamand Arnold, 1995). However, some data are inconsis-tent with the hypothesis that gonadal secretions nor-mally induce development of the more robust songsystem in males compared to females. Studies usingaromatase inhibitors or estrogen receptor antagonistsin males, or the induction of functional testiculartissue in genetic females, have produced either nega-tive data or results opposite to those predicted ifgonadal sex steroids normally induce masculinization(Mathews et al., 1988; Mathews and Arnold, 1990;Wade and Arnold, 1994, 1996; Wade et al., 1996,1999). In contrast, estrogen produced in the brainmasculinizes the projection from HVC to RA (Hollo-way and Clayton, 2001). Thus, while it seems thataxonal growth is regulated by neural estradiol, otheraspects of sexual differentiation may not be.Whether or not hormones trigger the process, it islikely that differential gene/protein expression is im-portant in the development of male and female brains.The