Review Incorporating Mouse Genome Mammalian Genome 12, 485–494 (2001). © Springer-Verlag New York Inc. 2001 DOI: 10.1007/s003350040002 Molecular basis of pituitary dysfunction in mouse and human Lisa J. Cushman, Sally A. Camper Department of Human Genetics, 4301 MSRBIII, 1500 W. Medical Center Drive, University of Michigan Medical School, Ann Arbor, Michigan 48109-0638, USA Received: 20 December 2000/ Accepted: 5 February 2001 The pituitary gland functions as an intermediary between the brain the process of pituitary gland organogenesis has been described in and the peripheral endocrine organs of the body (Tortora and recent years (Table 1). Homeobox genes critical for the develop- Grabowski 1996). In the context of a complex system of feedback ment of the anterior pituitary include the LIM homeodomain tran- control, the pituitary gland relays signals from the hypothalamus to scription factor Lhx3, the ‘paired’-like homeodomain transcription its target organs by secreting various hormones. These hormone factors Hesx1 (also known as Rathke’s pouch homeobox or Rpx) signals, which are transmitted throughout the endocrine system, and Prop1, and the POU homeodomain transcription factor Pit1 reflect the current homeostatic conditions of the body. Mecha- (Li et al. 1990; Sheng et al. 1996; Sornson et al. 1996; Dattani et nisms of compensation, including the regulation of gene transcrip- al. 1998). The nuclear receptor steroidogenic factor 1 (SF1) also tion, hormone secretion, and cell proliferation, allow the pituitary plays a significant role in pituitary gland development and function to respond to the continually changing needs of the organism. It is (Ingraham et al. 1994; Luo et al. 1994; Zhao et al. 2000). These in this way that the pituitary aids in the regulation of many vital genes, along with a number of other transcription factor genes processes, including growth, metabolism, reproduction, and stress expressed in the developing pituitary, comprise a genetic hierarchy response. essential for proper pituitary gland ontogeny (Fig. 1). The mammalian pituitary is comprised of three lobes: the pos- In the mouse, the development of Rathke’s pouch begins at terior lobe, the intermediate lobe, and the anterior lobe. The ante- approximately embryonic day 8.5 (e8.5; Dubois and ElAmraoui rior lobe of the pituitary is composed of functionally distinct cell 1995). Lhx3 is one of the genes that play an important role in this types that are the primary site of endocrine regulation. During process (Sheng et al. 1996). The formation of a definitive pouch embryogenesis, the anterior and intermediate lobes of the pituitary during pituitary organogenesis requires the expression of Lhx3, or develop from an invagination in the oral ectoderm known as Rath- its family member Lhx4 (Sheng et al. 1997). In the mouse, the ke’s pouch (Dubois and ElAmraoui 1995). The pouch eventually expression of Lhx3 is restricted to neural and neuroendocrine cells separates from the oral ectoderm and undergoes a period of intense (Dawid et al. 1995; Sheng et al. 1997). Its expression is detected proliferation. This is followed by differentiation into the five an- in the pituitary gland, motor neurons of the spinal cord, motor terior pituitary cell types on the rostral side of the pouch and the neurons in the hindbrain, the retina, and the pineal gland. Lhx3 intermediate lobe melanotropes on the caudal side of the pouch expression is first evident in the developing pouch at e9.5 and (Dubois and Hemming 1991). By birth, the anterior pituitary is persists in the pituitary throughout adulthood. In Lhx3-/-mice, pi- composed of functioning corticotropes, thyrotropes, somatotropes, tuitary development is arrested after initial pouch commitment gonadotropes, and lactotropes that produce adrenocorticotropic (Sheng et al. 1996). Rathke’s pouch forms in these mice, but fails hormone (ACTH), thyroid-stimulating hormone (TSH), growth to grow and differentiate. Lhx3 expression is also required for the hormone (GH), gonadotropins (FSH and LH), and prolactin (PRL), differentiation and proliferation of four anterior pituitary cell respectively. Expression of each hormone gene, which defines the types. The pituitary glands of Lhx3-deficient mice lack somato- terminal differentiation of each cell type, occurs in a spatially and tropes, lactotropes, thyrotropes, and gonadotropes (Sheng et al. temporally specific manner during pituitary organogenesis (Japon 1996). While corticotrope differentiation is initiated in these ani- et al. 1994; Burrows et al. 1999). The mechanisms that control this mals, they fail to expand and/or survive, leading to an absence of process involve the secretion of signals from surrounding struc- corticotropes at birth. In addition, loss of Lhx3 results in a failure tures and the expression of a cascade of homeodomain transcrip- to maintain Hesx1 expression and activate Pit1 expression. These tion factors. Studies in both mouse and human reveal that control findings are consistent with the transactivation capabilities of of signaling events and homeobox gene expression is essential for LHX3. In vitro experiments have revealed that LHX3 can trans- proper pituitary gland development (Watkins-Chow and Camper activate the promoters of several pituitary hormone markers, in- 1998; Dasen and Rosenfeld 1999). Deregulation of these events cluding PRL, TSH␤, and ␣GSU (the ␣ subunit of the glycoprotein can lead to various forms of pituitary gland dysfunction, including hormones LH, FSH, and TSH, also known as Cga) (Sloop et al. hypopituitarism and adenomas. 1999). LHX3 can also activate transcription of the Pit1 gene. As a result of their developmental abnormalities, Lhx3-/-mice die at or Transcription factor genes in anterior pituitary development shortly after birth (Sheng et al. 1996). Lhx4-/-mice exhibit com- mitment and differentiation of all five cell types, but in substan- Studies involving spontaneous mouse mutants and engineered tially reduced numbers (Sheng et al. 1997). In contrast to both mouse models have helped elucidate the role transcription factor Lhx3-/-mice and Lhx4-/-mice, pituitary gland development in mice genes play in pituitary gland ontogeny (Watkins-Chow and lacking both Lhx3 and Lhx4 is arrested prior to the formation of a Camper 1998). The function of numerous transcription factors in definitive pouch (Sheng et al. 1997). These data indicate that either Lhx3 or Lhx4 is required for the formation of a definitive pouch. In addition, Lhx3 expression is essential for pouch expansion and Correspondence to: S.A. Camper; E-mail: [email protected] differentiation of most anterior pituitary cell types. 486 L.J. Cushman, S.A. Camper: Pituitary dysfunction in mouse and human Table 1. Transcription factors critical for pituitary development and function. Gene Class Model Phenotype Reference Egr1 Zinc finger Knockout Reduced growth, female infertility, no Lhb expression, reduction in Topilko et al. 1998; Lee et al. 1996 somatotrope number Gata2 Zinc finger Knockout Embryonic lethal at e10–e11 due to severe anemia Tsai et al. 1994 Gata2 Zinc finger Dominant An absence of Lhb and SF-1 (Nr5a1) expression; reduced Tshb Dasen et al. 1999 negative Tg and ␣Gsu expression Lhx3 LIM HD Knockout RP forms but fails to expand and differentiate; hypoplastic pituitary Sheng et al. 1996 lacks GH, TSH, PRL, FSH, LH cells; corticotropes initiate differentiation but fail to expand Lhx4 LIM HD Knockout Hypoplastic pituitary with reductions in all cell types Sheng et al. 1997 Otx1 Bicoid-like HD Knockout Transient hypogonadism and dwarfism; delayed production of FSH, Acampora et al. 1998 LH, and GH; recovered by 4 months of age Pax6 Paired-like HD Knockout Ventralization of dorsoventral axis of pituitary gland Kioussi 1999 Pit1 POU HD Snell dwarf Missing thyrotropes, somatotropes, and lactotropes; increased Li et al., 1990 gonadotropes; exhibit dwarfism, hypothyroidism, and infertility Pitx1 Bicoid-like HD Knockout Decreased levels of LH, FSH, and TSH; increased levels of ACTH; Szeto et al. 1999; Lanctot et al. 1999 die at P1 with cleft palate and limb defects Pitx2 Bicoid-like HD Knockout Embryonic lethal at e15; defects of the ventral body wall, heart, Gage et al. 1999; Kitamura et al. 1999; eyes, and teeth; pituitary development arrested at e12.5 Lu et al. 1999; Lin et al. 1999 Prop1 Paired-like HD Ames dwarf Near absence of thyrotropes, somatotropes, and lactotropes; Sornson et al. 1996; Gage et al. 1996b reduced production of LH and FSH; exhibit dwarfism, hypothyroidism, and infertility Hesx1 Paired-like HD Knockout Anterior CNS defects; bifurcated and hypoplastic RP Dattani et al. 1998 (Rpx) Nr5a1 (SF1) Nuclear receptor Knockout Lethal by P8 due to adrenal insufficiency; lack gonads; exhibit Ingraham et al. 1994; Luo defects of the VMH; fail to produce LH and FSH et al. 1994 HD, homeodomain; Tg, transgene; GH, growth hormone; TSH, thyroid stimulating hormone; PRL, prolactin; FSH, follicle stimulating hormone; LH, luteinizing hormone; ACTH, adrenocorticotropic hormone; CNS, central nervous system; RP, Rathke’s pouch; VMH, ventromedial hypothalamus. gin to disappear in a spatially and temporally specific sequence that corresponds to progressive pituitary cell differentiation. Tar- geted deletion of the Hesx1 gene results in variable anterior central nervous system defects, including reduced prosencephalon, eye anomalies, and defects in olfactory development (Dattani et al. 1998). In the pituitary gland, an absence of functional HESX1 leads to abnormal bifurcations in